Chăm Sóc Và Điều Trị Bỏng Toàn Diện (Total Burn Care – Tập 5)

18  •  Respiratory Care
196
areas and vibrating into the patient, isometrically contract­
ing or tensing the muscles of their arms and shoulders.
Mechanical vibrations have been reported to be clinically
effective. Gentle mechanical vibration may be indicated for
patients who cannot tolerate manual percussion (Fig. 18.3).
Chest physiotherapy techniques should be used every 2–4 h
for patients with retained secretions.
EARLY AMBULATION
Early ambulation is another effective means of preventing
respiratory complications. Patients routinely should be
helped out of bed on postoperative days 3–5, and they
should be encouraged to ambulate and sit in a chair. With
the appropriate use of analgesics, even patients on continu­
ous mechanical ventilation can be helped out of bed and
into a chair (Fig. 18.4). The rocking chair (Fig. 18.5) has
several beneficial effects:
■ the patient can breathe with regions of the lungs that
are normally hyperventilated,
■ muscular strength and tone are preserved, and
■ contractions are prevented and exercise tolerance is
maintained.9
arterial oxygenation may fall during bronchial drainage/
positioning.7 Therefore, it is common practice in intensive
care units to turn patients side to side every 2 h to aid in
mobilizing secretions (Fig. 18.1).
Percussion
Percussion aids in the removal of secretions from the tra­
cheal bronchial tree. It is performed by cupping the hand to
allow a cushion of air to enter between the therapist’s hand
and the patient. If this is done properly, a popping sound
will be heard when the patient is percussed. There should
be a towel between the patient and the therapist’s hand in
order to prevent irritation of the skin.8 Percussion is applied
over the surface landmarks of the bronchial segments that
are being drained. The hands rhythmically and alternately
strike the chest wall. Incisions, skin grafts, and bony promi­
nences should be avoided during percussion (Fig. 18.2).
Vibration/Shaking
Vibration/shaking is a movement used to move loose secre­
tions to larger airways so that they can be coughed up or
removed by suctioning. Vibration involves the rapid shaking
of the chest wall during exhalation. The percussor vibrates
the thoracic cage by placing both hands over the percussed
Box 18.1  Inhalation Injury Treatment Protocol
■ Titrate humidified oxygen to maintain SaO2s >90%
■ Cough, deep breath exercises every 2 h
■ Turn patient side to side every 2 h
■ Chest physiotherapy every 4 h
■ Aerosolize 3 cc of 20% N-acetylcysteine every 4 h with a
bronchodilator
■ Alternate aerosolizing 5000 units of heparin with 3 cc of
normal saline every 4 h
■ Nasotracheal suctioning as needed
■ Early ambulation on postoperative day 5
■ Sputum cultures for intubated patients every M-W-F
■ Pulmonary function studies prior to discharge and at
outpatient visits
■ Patient/family education regarding inhalation injury
■ The protocol is continued for 7 days.
Fig. 18.1  Patient positioning for secretion mobilization.
Fig. 18.2  Chest physiotherapy techniques.
Fig. 18.3  Gentle mechanical chest vibrations.

18  •  Respiratory Care
197
larynx. The operator then listens for air sounds at the
proximal end of the catheter. When airflow is felt to be
strongest and respiratory sounds are loudest, the tip of the
catheter is immediately above the epiglottis. On inspiration,
the catheter is advanced into the trachea. After the vocal
cords have been passed, a few deep breaths are allowed
and the patient is reoxygenated. Suction begins while the
catheter is slowly withdrawn from the trachea. The patient
should not be suctioned for more than 15 s without being
reoxygenated.
Suctioning is not without potential hazards.14,15 Compli­
cations include irritation of the nasotracheal mucosa with
bleeding, abrupt drops in PO2, vagal stimulation, and bra­
dycardia. Preoxygenating and limiting suction time have
been shown to decrease or eliminate the fall in the PO2.12–14
Sputum cultures should be performed for microbiological
identification when they are clinically indicated.
THERAPEUTIC BRONCHOSCOPY
When all other techniques fail to remove secretions, the use
of the fiberoptic bronchoscope may be beneficial. In addi­
tion to its diagnostic functions, bronchoscopy retains
important therapeutic applications. The fiberoptic broncho­
scope is small in diameter, flexible, and has a steerable tip
that can be maneuvered into the fourth- or fifth-order
bronchi for examination or specimen removal. Copious
secretions encountered in patients with inhalation injury
may require repeated bronchoscopic procedures when
more conservative methods are unsuccessful.
PHARMACOLOGIC ADJUNCTS
Bronchodilators can be helpful in select cases. Inhala­
tion injury to the lower airways results in a chemical
tracheobronchitis, which can produce wheezing and bron­
chospasms. Most drugs used in the management of bron­
chospasms are believed to control bronchial muscle tone.
Aerosolized sympathomimetic are effective in two ways:
they cause bronchial muscle relaxation, and they stimu­
late mucociliary clearance. A newer compound of note is
metaproterenol, which is available as a cartridge inhaler,
as an aerosolized liquid, as a tabular oral medication, or
as a syrup. The recommended oral dose is 10–20 mg every
6–8 h, or 1–2 puffs every 3–4 h as an inhaled bronchodila­
tor with a duration of action of 1–5 h.16
Albuterol can also be aerosolized or be administered
orally or parenterally. Albuterol is available in a metered
cartridge inhaler, and its standard dose is 1–2 puffs three to
four times daily. Aerosolized albuterol has a duration of
action of approximately 4–6 h.17
Racemic epinephrine is used as an aerosolized topical
vasoconstrictor, bronchodilator, and secretion bond breaker.
The vasoconstrictive action of racemic epinephrine is useful
in reducing mucosal and submucosal edema within the
walls of the pulmonary airways. A secondary bronchodila­
tor action serves to reduce potential spasms of the smooth
muscles of the terminal bronchioles. Water, employed as a
diluent for racemic epinephrine, serves to lower both adhe­
sive and cohesive forces of the retained endobronchial
secretions, thus serving as a bond-breaking vehicle. Racemic
epinephrine has also been used for the treatment of
AIRWAY SUCTIONING
Airway suctioning is another method of clearing an airway.
Normal bronchial hygiene is usually accomplished by the
mucociliary escalator process. When these processes are
not effective in maintaining a clear airway, tracheobron­
chial suctioning is recommended.10–13 Nasotracheal suc­
tioning is intended to remove accumulated secretions and
other foreign material from the trachea that cannot be
removed by the patient’s spontaneous cough or by less inva­
sive procedures. Nasotracheal suctioning refers to the inser­
tion of a suction catheter through the nasal passages and
pharynx into the trachea in order to aspirate secretions or
foreign material.
The first step in this process is to hyperoxygenate the
patient with 100% oxygen. The patient should be posi­
tioned in the Fowler’s position, and the catheter slowly
advanced through the nares to a point just above the
Fig. 18.4  Early ambulation.
Fig. 18.5  Patient up out of bed, secretions being mobilized by rocking,
and chest physiotherapy techniques.

18  •  Respiratory Care
198
are recommended for the entire length of the aerosolized
treatments.
Mechanical Ventilation
Over the past 30 years, and particularly over the past
decade, there has been an increase in new ventilation tech­
niques that present alternatives for the treatment of patients
with smoke inhalation. Unfortunately, although the number
of options available to the clinician has appeared to increase,
randomized and placebo-controlled clinical trials defining
the specific role for each mode of ventilation and comparing
them to other modes of ventilation have not been forthcom­
ing. The recommendations from the American College of
Chest Physicians Consensus Conference on Mechanical
Ventilation serve as general guidelines.27 The consensus
concludes:
■ The clinician should choose a ventilator mode that has
been shown to be capable of supporting oxygenation
and ventilation and that the clinician has experience
in using.
■ An acceptable oxygen saturation should be targeted.
■ Based primarily on animal data, a plateau pressure of
greater than 35 cm H2O is cause for concern. However,
with clinical conditions that are associated with a
decreased chest wall compliance, plateau pressures
greater than 35 cm H2O may be acceptable.
■ To accomplish the goal of limiting plateau pressures,
PCO2 values should be permitted to rise (permissive
hypercapnia) unless other contraindications exist that
demand a more normal PCO2 or pH.
■ Positive end-expiratory pressure (PEEP) is useful in
supporting oxygenation. An appropriate level of PEEP
may be helpful in preventing lung damage. The level of
PEEP required should be established by empirical trials
and reevaluated on a regular basis.
■ Large tidal volumes (10–12 mL/kg) with PEEP may be
needed to improve oxygenation if the use of protective
ventilation strategies becomes ineffective. Peak flow
rates should be adjusted as needed to satisfy patient
inspiratory needs.57 Care must be taken to avoid the
consequences of utilizing high ventilator pressures if
large tidal volumes are required.
Animal studies showed a reduction in ventilator-induced
injury with a reduction in plateau pressures to 35 cm H2O
by increasing PEEP and decreasing tidal volume.28 A
number of clinical trials have been conducted to support
this treatment strategy.29–31 A meta-analysis of these trials
was conducted by the Cochrane Anesthesia Review Group
in 2007.32 It showed a reduction in mortality and duration
of mechanical ventilation with the use of plateau pressure
at less than 30 cm H2O and tidal volume at less than 7 mL/
kg body weight. In light of this evidence, the tidal volumes
used when initiating mechanical ventilation should be
6–8 mL/kg of predicted body weight. If the patient becomes
obstructed with fibrin cast and presents with an acute
increase in PCO2 and decrease in PaO2, the clinician should
first provide aggressive pulmonary toilet, then consider
changing over to volume ventilation with higher tidal
volumes. If ventilation continues to worsen, tidal volumes
postextubation stridor.18 Its mode of action is thought to be
related to the vasoconstrictive activity, with the resultant
decrease in mucosal edema. Aerosolized treatments may be
given every 2 h as long as the heart rate is not increased.
Hypertonic saline offers a theoretically more effective
form of mucokinetic therapy. The deposition of hypertonic
droplets on the respiratory mucosa causes the osmotic
attraction of fluids from the mucosal blood vessels and
tissues into the airway. Thus, a “bronchorrhea” is induced.
The watery solution helps dilute the respiratory tract secre­
tions and increase their bulk, thereby augmenting expecto­
ration. Furthermore, there is evidence that hypertonic
saline has a direct effect on the mucoprotein DNA com­
plexes, and, by reducing the cohesive intramolecular forces,
the salt helps reduce the viscous properties of the mucoid
fluid.19 Excessive use of hypertonic saline is not recom­
mended because burn patients cannot tolerate the sodium
load and may develop edema.
Oxandrolone is a synthetic testosterone analog that has
been shown to significantly reduced hypermetabolism and
significantly increased height percentile, bone mineral
content, lean body mass, and strength in pediatric burn
patients.20 Recently, it has been shown that pediatric
patients treated with oxandrolone for 1 year had signifi­
cantly higher maximum voluntary ventilation compared to
untreated patients. 21 Also, during maximal exercise, the
subjects treated with oxandrolone had a significantly higher
maximal ventilation (VEMax).21 The administration of oxan­
drolone may be used as an agent in the future to improve
lung function in burned patients.
Aerosolized acetylcysteine is a powerful mucolytic agent
in use in respiratory care. Acetylcysteine contains a thiol
group; the free sulfhydryl radical of this group is a strong
reducing agent which ruptures the disulfide bonds that give
stability to the mucoprotein network. Agents that break
down these disulfide bonds produce the most effective
mucolysis.22 Of note, acetylcysteine is an irritant to the
respiratory tract. It can cause mucosal changes, and it may
induce bronchospasms. For this reason, patients are evalu­
ated for signs of bronchospasms, and a bronchodilator may
be added if necessary. Acetylcysteine has proved to be effec­
tive in combination with aerosolized heparin for the treat­
ment of inhalation injury in animal studies.23
Last, heparin and acetylcysteine combinations have been
used as scavengers for the free oxygen radicals produced
when alveolar macrophages are activated either directly by
chemicals in smoke or by one or more of the compounds in
the arachidonic oxidative cascade.24 Animal studies have
shown an increased P/F ratio, decreased peak inspiratory
pressures, and a decreased amount of fibrin cast formation
with the heparin and acetylcysteine combination therapy.25
In a retrospective review, Desai et al. have shown that the
use of heparin and N-acetylcysteine is effective in pediatric
patients with inhalation injury.26 Results indicated a signifi­
cant decrease in the reintubation rates, the incidence of
atelectasis, and improved mortality for patients treated with
the combined therapy. Therefore, a standard treatment for
patients with inhalation injury may include 5000–10,000
units of heparin and 3 mL normal saline nebulized every
4 h, alternating with 3–5 mL of 20% acetylcysteine for 7
days. This ensures that the patient receives an aerosolized
treatment every 2 h. Baseline and daily clotting analyses

18  •  Respiratory Care
199
■ In each case, extra work is imposed on the patient
during spontaneous breaths.
Pressure Control Mode
In pressure-controlled ventilation all breaths are time- or
patient-triggered, pressure-limited, and time-cycled. The
length of inspiration, pressure level, and back-up rate are
set by the operator. The tidal volume is based on the compli­
ance and resistance of the patient’s lungs, the ventilator
system, and the preset pressure.
Pressure Support Ventilation
Pressure support ventilation (PSV) is a pressure-targeted,
flow-cycled mode of ventilation in which each breath must
be patient-triggered. It is used both as a mode of ventilation
during stable ventilation support periods and as a weaning
method.37–41 It is primarily designed to assist spontaneous
breathing; thus, the patient must have an intact respiratory
drive.
Advantages include:
■ It is generally considered a comfortable mode of venti­
lation for most patients,
■ Pressure support reduces the work of breathing,
■ It can be used to overcome airway resistance caused by
the endotracheal tube, and
■ Pressure support may be useful in patients who are
difficult to wean.
Disadvantages include:
■ The tidal volume is not controlled and it is dependent
on respiratory mechanics, cycling frequency, and syn­
chrony between the patient and ventilator, and
■ Pressure support may be poorly tolerated in some
patients with high airway resistances because of the
preset high initial flow rates.
ALTERNATE MODES OF VENTILATION
During the past decade, a new concept of ventilation has
emerged in the treatment of ARDS patients. In severe cases
of ARDS, only a small part of the lung parenchyma remains
accessible to gas delivered by mechanical ventilation.42,43 As
a consequence, tidal volumes of greater than 10 mL/kg may
overexpand and injure the remaining normally aerated lung
parenchyma. High airway pressures may result in overdis­
tension and local hyperventilation of more compliant parts
of the lung. Overdistension of lungs in animals has been
shown to produce diffuse alveolar damage.44–46 This is the
primary reason that alternative modes of ventilation, which
are all based on a reduction of end-inspiratory airway pres­
sures and/or tidal volumes delivered to the patient, have been
developed and are used by many clinicians caring for patients
with severe forms of acute or chronic respiratory failure.
The following four alternative modes of ventilation will be
discussed: high-frequency ventilation, high-frequency per­
cussive ventilation, airway pressure release ventilation, and
volumetric diffusive ventilation.
High-Frequency Ventilation
High-frequency ventilation (HFV) is the administration of
small tidal volumes of 1–3 mL/kg at high frequencies of
of 10–12 mL/kg may be needed to provide adequate
mechanical ventilation.57
MODES OF VENTILATION
Control Mode
In the control mode of ventilation, the ventilator automati­
cally cycles at a rate selected by the operator. The ventilator
will cycle regardless of the patient’s needs or desire for a
breath, but it guarantees a minimum level of minute venti­
lation in the sedated or paralyzed patient. This mode of
ventilation is often utilized in patients with acute respira­
tory distress syndrome (ARDS) because of the high peak
pressures needed to achieve adequate chest expansion. The
major disadvantage with this mode is that the patient
cannot cycle the ventilator; thus, the minute ventilation
must be set appropriately.
Assist-Control Mode
In the assist-control mode of ventilation, every breath is
supported by the ventilator and a back-up control rate is set.
The tidal volume, inspiratory flow rate, flow waveform, sen­
sitivity, and control rate are set.33–35 The advantages include
that assist-control ventilation combines the security of con­
trolled ventilation with the possibility of synchronizing the
breathing pattern of the patient and ventilator, and it
ensures ventilation support during each breath. Disadvan­
tages are as follows:
■ Excessive patient work occurs in case of inadequate
peak flow or sensitivity settings, especially if the venti­
lator drive of the patient is increased,33–35
■ It is often poorly tolerated in awake, nonsedated sub­
jects, and it can require sedation to insure synchrony
of patient and ventilator,
■ It can cause respiratory alkalosis, and
■ It may worsen air trapping with patients with chronic
obstructed lung disease (COPD).26
Synchronized Intermittent Mandatory Ventilation
Synchronized intermittent mandatory ventilation (SIMV)
combines a preset number of ventilator-delivered manda­
tory breaths of the present tidal volume with the facility for
intermittent patient-generated spontaneous breaths.36,37
The advantages are as follows:
■ The patient is able to perform a variable amount of
respiratory work, and the security of a preset manda­
tory level of ventilation is maintained,
■ SIMV allows for variation in the level of partial ventila­
tion support from near total ventilation support to
spontaneous breathing, and
■ It can be used as a weaning tool.
Disadvantages include:
■ Hyperventilation with respiratory alkalosis,
■ Excessive work of breathing due to the presence of a
poorly responsive demand valve, suboptimal ventila­
tion circuits, or inappropriate flow delivery could occur,
and

18  •  Respiratory Care
200
humidification of the respiratory gases or severe necrotizing
tracheobronchitis can occur. Special delivery devices for
providing adequate humidification during HFV are required.
It is not clear when and how it should be used following
inhalation injury.54 As the methodology for HFPV evolves,
it is anticipated that HFPV will play a larger role in the care
of select mechanical ventilation-dependent populations.55
Airway Pressure Release Ventilation
Airway pressure release ventilation (APRV) is a pressure-
regulated mode of ventilation support that allows for time-
cycled decreases in pressure to facilitate CO2 elimination.
This mode allows spontaneous breathing while limiting
airway pressures; therefore, it may limit the amount of seda­
tives or neuromuscular blocking agents needed. APRV is a
protective ventilator strategy that uses inverse ratio ventila­
tion at two levels of PEEP. Several limited studies have sug­
gested that APRV may be beneficial for the treatment of burn
patients who develop ARDS. Evidence-based recommenda­
tions to use this mode of ventilation await outcome studies.
VOLUMETRIC DIFFUSIVE VENTILATION
The volumetric diffusive ventilator (VDR) is a pneumatically
powered, pressure-limited ventilator that stacks oscillatory
breaths to a selected peak airway pressure by means of a
sliding venturi called a phasitron. After inspiration, exhala­
tion is passive and ends at a selected level of oscillatory
CPAP.56 Studies comparing VDR to high-volume strategies
have shown VDR improves gas exchange, decreases peak
pressures, and lowers mortality. However, there is a need to
compare VDR to the low tidal volume ventilation practiced
more recently. Usage of the VDR requires special training;
the other disadvantages are the inability to monitor tidal
and minute volumes and the requirement of humidified air
and nebulized saline to prevent airway desiccation.
VENTILATOR SETTINGS
A large multicentered study by the Acute Respiratory Dis­
tress Syndrome Network evaluated the use of volume ven­
tilation with low versus high tidal volume on ARDS. This
study documented a decreased incidence of mortality in
patients with ARDS who were ventilated with small tidal
volumes.29 Based on this study in 2000, it has become clini­
cally accepted practice to use low tidal volumes when ini­
tially setting up mechanical ventilation (Table 18.2).
100–3000 cpm.47 This mode of ventilation is based on a
marked reduction in tidal volumes and airway pressures,
and it has the greatest potential for reducing pulmonary
barotraumas. There are a number of different types of high-
frequency ventilation techniques. The two most common
are high-frequency jet ventilation (HFJV) and high-
frequency percussive ventilation (HFPV).
HFJV is the only high-frequency mode routinely used to
ventilate patients with ARDS, and it is primarily used in
Europe.27 This type of ventilation uses a brief jet of gas at a
high frequency. Comparative data concerning the advan­
tages of HFJV over conventional ventilation are limited.
There is no agreement, however, that HFJV is better than
conventional mechanical ventilation in ARDS.48
HFPV has shown some promise in the ventilation of
patients with inhalation injury.49–51 HFPV refers to ventila­
tion utilizing the Volume Diffusive Respiration (VDR) venti­
lator, and it oscillates between the inspiratory and expiratory
airway pressures. Clinical studies indicate that this mode of
ventilation may aid in reducing pulmonary barotrauma.49,50
In a retrospective study, Cortiella et al. have shown a
decreased incidence of pneumonia, peak inspiratory pres­
sure, and an improved P/F ratio in children ventilated with
the use of HFPV compared to controls.52 In the first prospec­
tive randomized study of HFPV, Mlcak et al. have shown a
significant decrease in the peak inspiratory pressures
needed to ventilate pediatric patients with inhalation
injury.53 No significant differences were found for incidence
of pneumonia, P/F ratios, or mortality.
Based on clinical experience, the following guidelines are
suggested for initial set-up of the HFPV in children (Table
18.1). The pulsatile flow (PIP) rate should be set at 20 cm
H2O, the pulse frequency (high rate) should be set between
500 and 600, and the low respiratory rate should be set
between 15 and 20. Oscillatory PEEP levels should be ini­
tially set at approximately 3 cm H2O, and demand PEEP
should be set at 2 cm H2O. Ventilator settings are adjusted
based on the patient’s clinical condition and blood gas
values. To improve oxygenation, the ventilator can be
switched to a more diffusive mode (increased pulse fre­
quency); to eliminate carbon dioxide, the ventilator can be
switched to a more convective mode (decreased pulse fre­
quency). With HFPV, subtidal volumes are delivered in a
progressive stepwise fashion until a preset oscillatory equi­
librium is reached, and exhalation is passive.
Clinicians must be familiar with each technique used
and its possible limitations. There must be adequate
Table 18.1  High-Frequency Percussive Ventilation
Set-Up Guidelines
Variable
Settings
Pulsatile Flow Rate (PIP)
20 cm H2O
Pulse Frequency (high rate)
500–600
Low Respiratory Rate
15–20
I : E Ratio
1 : 1 or 2 : 1
Oscillatory PEEP
3 cm H2O
Demand PEEP
2 cm H2O
Table 18.2  Targeted Mechanical Ventilation Guidelines
in Children
Variable
Settings
Tidal Volumes
6–8 mL/kg
Respiratory Rate
12–45 breaths/min
Plateau Pressures
<30 cm H2O
I : E Ratio
1 : 1–1 : 3
Flow Rate
40–100 L/min
PEEP
7.5 cm H2O

18  •  Respiratory Care
201
areas. Arterial blood gases should be checked after the
patient has been on the ventilator for approximately 20 min
and the respiratory rate adjusted accordingly.
Flow Rates
The selection of peak inspiratory flow rate during volume
ventilation is primarily determined by the level of spontane­
ous inspiratory effort. In patients triggering volume breaths,
patient effort, work of breathing, and patient ventilator
synchrony depend on the selection of peak inspiratory
flow.34 Peak inspiratory flows should ideally match patient
peak inspiratory demands. This normally requires peak
flows to be set at 40–100 L/min, depending on expired
volume and the inspiratory demand.27
Inspiratory/Expiratory (I:E) Ratio
The time allowed for the inspiratory and expiratory phases
of mechanical ventilation is commonly referred to as the
inspiratory/expiratory (I:E) ratio. The inspiratory part of
the ratio includes the time to deliver the tidal volume before
the exhalation valve opens and exhalation begins. The expi­
ratory part of the ratio includes the time necessary for the
tidal volume to exit through the exhalation valve before the
next inspiration begins. The inspiratory time should be long
enough to deliver the tidal volume at flow rates that will not
result in turbulence and high peak airway pressures. Typi­
cally, the I : E ratio is 1 : 1 to 1 : 3.62
In severe lung disease, it is acceptable to prolong the
inspiratory time to allow for better distribution of gas and
to enhance oxygen diffusion. When a longer inspiratory
time is required, careful attention should be given to suffi­
cient expiration to avoid stacking of breaths and impeding
venous return. Prolonged inspiratory time creates a more
laminar flow, which helps to keep the peak pressures lower.
Fast inspiratory times are tolerated in patients with severe
airway obstruction. The fast inspiratory time allows for a
longer expiratory phase, which may help to decrease the
amount of overinflation.
Inspired Oxygen Concentration
As a starting point, a patient placed on a ventilator should
receive an oxygen concentration of 100%. The concentra­
tion should be systematically lowered based on values from
arterial blood gases. Generally, as a result of the concerns
regarding the effects of high oxygen concentration on lung
injury, the lowest acceptable oxygen level should be selected
as soon as possible. In patients who are difficult to oxygen­
ate, oxygen concentrations can be minimized by optimizing
PEEP and mean airway pressures and selecting minimally
acceptable oxygen saturation.63
Positive End-Expiratory Pressure
PEEP is applied to recruit lung volumes, elevate mean
airway pressure, and improve oxygenation.64 The level
of PEEP used varies with the disease process. PEEP levels
should start at 8–10 cm H2O and should be increased in
2.5-cm increments. Increasing levels of PEEP, in conjunc­
tion with a prolonged inspiratory time, aids in oxygenation
and allows for the safe percentage of oxygen to be used.
The use of pressure–volume curves to determine the best
PEEP level has been recommended to aid in overstretching
the alveoli. The process of using the curves is difficult to
Tidal Volumes
In volume-cycled ventilation, a machine-delivered tidal
volume is set to be consistent with adequate gas exchange
and patient comfort. The tidal volume selected for burned
patients normally varies between 6 and 8 mL/kg of pre­
dicted body weight. Numerous factors, such as lung/thorax
compliance, system resistance, compressible volume loss,
oxygenation, ventilation, and barotrauma, are considered
when volumes are selected.53 Sousse et al. have recently
shown that the use of higher tidal volumes in pediatric burn
patients with inhalation injury may decrease the incidence
of ARDS and atelectasis as well as the number of days on a
ventilator when compared to lower tidal volumes.57 Of criti­
cal importance is the avoidance of overdistension. This can
generally be accomplished by ensuring that peak airway
and alveolar pressures do not exceed a maximum target.
Many would agree that a peak alveolar pressure greater
than 35 cm H2O in adults raises concern regarding the
development of barotrauma, and ventilator-induced lung
injury increases.58,59 Expired tidal volumes should be mea­
sured for accuracy at the connection between the patient’s
wye and the artificial airway.
The range of tidal volumes will vary depending on the
disease process, with some diseases requiring maximum
tidal volumes and others needing less. Severe interstitial
diseases such as pneumonia and ARDS may require a tidal
volume of greater than 8 mL/kg to adequately inflate the
lungs and improve gas exchange if protective ventilation
strategies become inadequate.
Respiratory Rate
Setting of the mandatory respiratory rate is dependent on
mode of ventilation selected, delivered tidal volume, dead
space-to-tidal volume ratio, metabolic rate, targeted PCO2
levels, and level of spontaneous ventilation. With adults,
the set mandatory rate normally varies between 4 and 20
breaths/min, with most clinically stable patients requiring
mandatory rates in the 8–12 range.60 It is important to have
targeted arterial blood gas values set to aid the clinical team
in proper management (Table 18.3). Along with the Pco2,
pH, and patient comfort, the primary variable controlling
the selection of the respiratory rate is the development of
air trapping and auto PEEP.61
The respiratory rates of children and infants all need to
be set substantially higher than those of adults. For pediat­
rics, the respiratory rate can be set from 12 to 45, depend­
ing on the disease state and the level of targeted PCO2 one
wishes to achieve. Slower respiratory rates are useful in the
patient with obstructed airways because slower rates allow
more time for exhalation and emptying of hyperinflated
Table 18.3  Arterial Blood Gas Goals
Variable
Goal
pH
7.25–7.45
PO2
55–80 mm Hg or SaO2 of 88–95%
PCO2
35–55 mm Hg (permissive hypercapnia can be used
as long as pH >7.25)

18  •  Respiratory Care
202
intubation.76,77 The incidence of pneumonia developing is
estimated to be five times higher for intubated than non­
intubated patients, and tracheostomy increases this risk
even higher.78 Exposure to respiratory care equipment
adds an increased risk of pneumonia above and beyond
the risk associated with endotracheal intubation.79,80
After the use of nebulization equipment in respiratory
care became popular, several epidemics of nosocomial
pneumonia were reported.81 The risk of pneumonia from
mechanical ventilators was significant, but it decreased
with better understanding of the necessity to decontami­
nate respiratory equipment.82,83 Respiratory care equip­
ment, if not properly cared for, may provide a source of
extraneous organisms that can contaminate the patient’s
respiratory tract.
The potential role of respiratory care equipment in pro­
viding reservoirs for organisms that are capable of infecting
the lungs is well established. This problem, particularly per­
taining to reservoir devices and medications, has been rec­
ognized for a number of years, and effective control
strategies have been developed. Most hospitals maintain a
bacteriological monitoring system, and significant contam­
ination by this route is not likely.84 Nebulization equipment
delivers a fine-particle aerosol, and, if contaminated, the
aerosol droplets may contain bacteria.
Bag-mask units have been shown to allow the persistence
of infectious organisms and the subsequent infection of
other patients on whom the equipment has been later
used.85 Also, ventilator circuits are inevitably contaminated
by the patient’s own respiratory tract flora during exhala­
tion and coughing, and the fluid that collects in this tubing
is thereby contaminated. However, the American Associa­
tion for Respiratory Care evidence-based clinical practice
guidelines suggest that ventilator circuits should not be
changed routinely for infection control purposes.86
HANDWASHING
Handwashing is generally considered the single most
important procedure for preventing nosocomial infections.
The recommended handwashing procedures depend on the
purpose of washing. In most situations, a vigorous brief
washing with soap and water is adequate to remove tran­
sient flora. Antimicrobial handwashing procedures are
indicated before all invasive procedures, during the care of
patients in strict respiratory or enteric isolation, and before
entering intensive care units. The most commonly used
agents are 70% isopropyl alcohol, iodophors, and chlorhex­
idine. Scrub regimens such as povidone-iodine surgical
scrub are appropriate as well.87
CHEMICAL AGENTS FOR STERILIZATION/
DISINFECTION
Disinfectants act to kill microorganisms by several methods:
■ oxidating microbial cells,
■ hydrolyzing,
■ combining with microbial proteins to form salts,
■ coagulating the proteins of microbial cells,
■ denaturing enzymes, and/or
■ modifying cell wall permeability.88
perform in the clinical setting. However the use of PEEP trials
can determine the best PEEP without decreasing cardiac
output.
Optimal PEEP is the level of end-expiratory pressure that
results in the lowering of intrapulmonary shunting, signifi­
cant improvement in arterial oxygenation, and only a small
change in cardiac output, arteriovenous oxygen content
differences, or mixed venous oxygen tension. To determine
the optimal PEEP for patients with ARDS, the ARDS Network
performed a multicenter, randomized, prospective clinical
trial.64 ARDS patients were treated with 6 mL/kg predicted
body weight tidal volumes and randomized to either low
(5 cm H2O up to 24) or high (12 cm H2O up to 24) PEEP.
The trial showed no effect of higher levels of PEEP on dura­
tion of mechanical ventilation, duration of nonpulmonary
organ failure, and in-hospital mortality.
EXTUBATION CRITERIA
Standard extubation criteria include a wide variety of phys­
iologic indices that have been proposed to guide the process
of discontinuing ventilation support. Traditional indices
include:
■ PaO2/FIO2 ratio of greater than 250,
■ Maximum inspiratory pressure of greater than 60 cm
H2O,
■ Vital capacity of at least 15–20 mL/kg,
■ Spontaneous tidal volume of at least 5–7 mL/kg,
■ Maximum voluntary ventilation of at least twice the
minute volume,66–69 and
■ Audible leak around the endotracheal tube must be
present.
In general, these indices evaluate a patient’s ability to
sustain spontaneous ventilation. They do not assess a
patient’s ability to protect the upper airway. For this reason,
traditional indices often fail to reflect the true clinical picture
of a patient with an inhalation injury. For a complete evalu­
ation prior to extubation, bronchoscopic examination will
aid in determining if the airway edema has decreased
enough to attempt extubation. Prior to a scheduled extuba­
tion, it is recommended that reintubation equipment be set
up and that the person doing the extubation be experienced
in emergency intubations. If the patient demonstrates signs
of inspiratory stridor, the use of racemic epinephrine by
aerosol has been shown to be effective in reducing mucosal
edema and may prevent the patient from being
reintubated.18
Infection Control of
Respiratory Equipment
Pneumonia has become one of the most frequent, life-
threatening infections, and its incidence has become an
important determinant of mortality in burned patients.68
The majority of pneumonias are nosocomial, occur in
burned patients after 72 h of hospitalization, and are often
associated with either an inhalation injury or endotracheal
intubation with exposure to respiratory care equipment,
or both.70–75 One of the most important risk factors predis­
posing to pneumonia in burned patients is endotracheal

18  •  Respiratory Care
203
require surgical correction. In the management of intu­
bated patients, such complications should be mostly pre­
ventable by meticulous attention to the tracheostomy or
endotracheal tube cuff. Inflation of the cuff should be to the
minimal pressure level consistent with preventing a leak in
the ventilator at end inspiration.
OBSTRUCTIVE/RESTRICTIVE DISEASE
Chronic airway disease is a relatively rare reported sequel
of inhalation injury and its supportive treatment. Spirom­
etry is a useful screening tool for airway obstruction.
Reports in the literature for adults indicate that lung func­
tion returns to normal after inhalation injury.90,91 However,
Mlcak et al. reported pulmonary function changes follow­
ing inhalation injury for up to 10 years post-injury in a
group of severely burned children.92 In the great majority
of cases, eventual resolution of both symptoms and physi­
ologic abnormalities will occur. During the resolution
phase, serial measurement of airflow obstruction should be
obtained.93 Desai et al. demonstrated that physiologic
insults that occur as a result of thermal injury may limit
exercise endurance in children.94 Data from exercise stress
testing showed evidence of a respiratory limitation to exer­
cise. This was confirmed by a decrease in the maximal heart
rate, decrease in the maximal oxygen consumption, and
increase in respiratory rate. In the cases of persistent severe
respiratory symptoms, the severity of the impairment
should be documented and the patient evaluated for a pul­
monary rehabilitation program.
Summary
Inhalation injury and associated major burns provide
a challenge for healthcare workers who provide direct
hands-on care. The technical and physiologic problems that
complicate the respiratory management of these patients
require a practical knowledge of the possible sources of
nosocomial infections. Patients with inhalation injury
frequently require the use of respiratory care equipment
that, if not properly cared for, can aid in the spread of infec­
tions. Important priorities for reducing the risk of infections
include an aggressive bronchial hygiene therapy program,
adherence to established infection control practices, the use
of universal precautions during procedures, and meticu­
lous cleaning of respiratory care equipment, as well as
routine epidemiologic surveillance of the established infec­
tion control practices within each institution. It is impera­
tive that a well-organized, protocol-driven approach to
respiratory care of the burn patient be utilized so that
further improvements can be made and the morbidity and
mortality associated with inhalation injury be reduced.
Complete references available online at
inkling.com.
Further Reading
Acute Respiratory Distress Syndrome Network. Ventilation with lower
tidal volumes as compared with traditional tidal volumes for acute lung
injury and the acute respiratory distress syndrome. N Engl J Med.
2000;342(18):1301-1308.
Aldehydes
Aldehydes contain some of the most commonly used anti­
microbials in respiratory care practice. These agents achieve
their antimicrobial action through the alkylation of
enzymes.
The cidal action of glutaraldehyde is accomplished by
disruption of the lipoproteins in the cell membrane and
cytoplasm of vegetative bacterial forms. This reaction
between the chemical glutaraldehyde and cell proteins
depends on both time and contact. Items to be disinfected
must be free of material that would inhibit contact, and
adequate contact time is needed for the chemical reaction
to be complete. Alkaline glutaraldehyde, buffered by a 0.3%
bicarbonate agent, is used as a 2% solution. This solution is
bactericidal, virucidal, and tuberculocidal within 10 min
and produces sterilization when applied for 10–20 h. Equip­
ment disinfected or sterilized with glutaraldehyde should be
thoroughly rinsed and dried prior to use because any residue
would be irritating to mucous membranes.
Glutaraldehyde solutions are commonly used for cold dis­
infection or sterilization of respiratory care equipment, and
they have a large degree of safety. These solutions can be
used to disinfect bronchoscopes as well as many of the
current respiratory supplies.
Alcohols
Alcohols, especially ethylene and isopropyl alcohol, are
perhaps the most commonly used disinfectants. Alcohols as
a chemical family have many desirable characteristics
needed in disinfectants. They are generally bactericidal and
accomplish their bactericidal activity by damaging the cell
wall membrane. They also have the ability to denature pro­
teins, particularly enzymes called dehydrogenases. For
alcohol to coagulate microbial proteins, water must be
present. For this reason, 70% has been considered the criti­
cal dilution for alcohol, with a rapid loss of bactericidal
activity with dilutions less than 50%. Both ethyl and isopro­
pyl alcohols are rapidly effective against vegetative bacteria
and tubercle bacilli but are not sporicidal.
To be sure that the current infection control practice is
effective in each institution, random microbiological cul­
tures should be done whenever a problem is suspected or to
test the reliability of the disinfection or sterilization
techniques.
Late Complications of
Inhalation Injury
TRACHEAL STENOSIS
Tracheal complications are commonly seen and consist of
tracheitis, tracheal ulcerations, and granuloma formation.
The location of the stenosis is almost invariably subglottic
and occurs at the site of the cuff of the endotracheal or
tracheostomy tube.89 Several problems arising after extuba­
tion represent sequelae of laryngeal or tracheal injury
incurred during the period of incubation. While tracheal
stenosis or tracheomalacia is usually mild and asymptom­
atic, each can present as severe fixed or dynamic upper
airway obstructions in some patients. These conditions can

18  •  Respiratory Care
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Cartotto R. Use of high frequency oscillatory ventilation in inhalation
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Mlcak R, Desai MH, Herndon DN. A prospective randomized study of high
frequency percussive ventilation compared to conventional mechanical
ventilation in pediatric patients with inhalatiron injury. J Burn Care
Rehabil. 2000;21(1):S158.

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205
The Systemic Inflammatory
Response Syndrome
TRACY TOLIVER-KINSKY, MAKIKO KOBAYASHI, FUJIO SUZUKI, and EDWARD R.
SHERWOOD
19 
known causes. This definition is very sensitive and non­
specific, and most of the SIRS criteria are also addressed
in other scoring systems of injury-induced physiologic
derangement, such as the Acute Physiology and Chronic
Health Evaluation (APACHE), Mortality Probability Model
(MPM), and Simplified Acute Physiology Severity (SAPS)
systems. Several investigators have criticized the defini­
tion of SIRS as being too sensitive and encompassing the
majority of ICU patients and certainly the vast majority
of patients suffering extensive thermal injury.2,3 The initial
definition of SIRS also did not address the continuum of
disease severity defined for sepsis. Criteria for the diagnosis
of severe sepsis included the additional derangements of
organ dysfunction, hypotension, and hypoperfusion. Evi­
dence of hypoperfusion included, but was not limited to,
the presence of lactic acidosis, oliguria, and altered mental
status. Septic shock was characterized by hypotension and
hypoperfusion in patients who were adequately volume
resuscitated or required treatment with catecholamines or
other vasoactive drugs to support cardiovascular function.
Muckart and Bhagwangee,2 in an effort to define a con­
tinuum of severity for SIRS, later proposed the categories
of severe SIRS and SIRS-associated shock. These conditions
were defined by the same criteria as severe sepsis and septic
shock in the absence of demonstrable infection. In its most
severe form, SIRS can induce organ injury and subsequent
multiple organ dysfunction syndrome (MODS).
Despite the limitations in the definitions of SIRS and
sepsis, most clinicians and investigators generally adopted
the SIRS concept. However the initial definition and criteria
were not felt to be optimized. To address these issues, a
second consensus conference was assembled in 2001.4 The
goal of this conference was to revisit the previously defined
criteria for SIRS and sepsis as well as to determine whether
revision of these criteria was indicated. The consensus was
that the concepts of sepsis and SIRS are useful, but the
diagnostic criteria are overly sensitive and nonspecific. The
participants added additional criteria that defined meta­
bolic, biochemical, and functional alterations associated
with SIRS and sepsis. Among these were hyperglycemia,
edema, elevated plasma C-reactive protein (CRP) concen­
tration, coagulation abnormalities, thrombocytopenia,
ileus, and hyperbilirubinemia. The group further proposed
a staging system for sepsis and SIRS that could be used to
stratify patients for prediction of outcome. This staging
system, termed PIRO, defined several criteria, including the
predisposition of patients to a poor outcome as determined
by premorbid conditions and possible genetic factors. Other
factors include the severity and type of insult, the host
Introduction
Burn patients, with or without inhalation injuries, com­
monly exhibit a clinical picture that is largely produced by
systemic inflammation. The term systemic inflammatory
response syndrome (SIRS) was introduced to designate the
signs and symptoms of this condition. SIRS has a continuum
of severity ranging from physiologic alterations such as
tachycardia, tachypnea, fever, and leukocytosis to refractory
hypotension and, in its most severe form, shock and multiple
organ system dysfunction. In thermally injured patients, the
most common cause of SIRS is tissue damage caused by the
burn itself. Sepsis, characterized by SIRS in the presence of
infection, is also common in burn patients and is a signifi­
cant cause of morbidity and mortality. Starting from a local
infection at the burn wound, an infected catheter tip, or
pulmonary infection, the spread of microbes and their toxins
can further potentiate systemic inflammation. Pathological
alterations of metabolic, cardiovascular, pulmonary, renal,
gastrointestinal, and coagulation systems occur as a result
of the hyperactive immune system. This chapter will review
current understanding of SIRS and the associated immu­
nological, cardiovascular, and pulmonary dysfunction that
occurs following trauma and thermal injury.
Definition of SIRS
The term systemic inflammatory response syndrome (SIRS)
was recommended by the American College of Chest
Physicians/Society for Critical Care Medicine (ACCP/SCCM)
consensus conference in 1992 to describe a systemic inflam­
matory process, independent of its cause.1 The proposal
was based on clinical and experimental results indicating
that a variety of conditions, both infectious and noninfec­
tious (i.e., burns, ischemia–reperfusion injury, multiple
trauma, pancreatitis), induce a similar host response. Two
or more of the following conditions must be present for the
diagnosis of SIRS to be made:
■ Body temperature of greater than 38°C or less than
36°C;
■ Heart rate of greater than 90 beats/min;
■ Respiratory rate of greater than 20/min or a PaCO2 of
less than 32 mm Hg;
■ Leukocyte count of greater than 12,000/µL, less than
4000/µL, or more than 10% immature (band) forms.
All of these pathophysiologic changes must occur as an
acute alteration from baseline in the absence of other

19  •  The Systemic Inflammatory Response Syndrome
206
tachycardia in conjunction with signs of decreased periph­
eral perfusion, such as decreased capillary refill, decreased
peripheral pulses, decreased urine output, altered mental
status, and cold/mottled extremities.9
Several studies have been conducted with the goal of
determining the prognostic value of the SIRS designation.
In the acute setting, SIRS has been demonstrated in the
majority of critically injured patients, and the intensity of
the response correlates directly with the severity of injury.3,10
The presence of SIRS within the first 24 hours after severe
injury has not served as a reliable predictor of mortality in
trauma or burn patients.3,10 However, the presence of shock
is an important predictor of poor outcome, particularly
when associated with MODS.2 In addition, the presence of
more than two of the SIRS criteria in the setting of acute
injury has correlated with increased morbidity and mortal­
ity.11,12 A study by Rangel-Frausto et al.12 showed that
trauma patients who did not meet SIRS criteria had a mor­
tality rate of 3%, compared to 6% in those with two SIRS
markers. Patients with three or four SIRS criteria had mor­
tality rates of 10% and 17%, respectively, whereas those
with culture-negative shock had a 46% death rate. Haga
et al.13 have shown that the persistence of SIRS for more
than 3 days in surgical patients is a harbinger of complica­
tions and is associated with increased morbidity. Talmor
et al.10 reported that persistence of SIRS to the second post­
operative day in high-risk surgical patients correlated with
an increased incidence of MODS. Additional studies have
shown that persistence of SIRS criteria for more than 3 days
in trauma and burn patients is associated with worse
outcome.13–16 Therefore, three important factors appear to
determine the effect of SIRS on the host. The first is the
severity of the initial inflammatory response. This response
is proportional to the severity of injury, and the presence of
shock or MODS within the first 24 hours after injury carries
a poor prognosis. The second determinant is the persistence
of SIRS beyond the first few days of injury. Specifically pro­
longation of SIRS beyond the second day after severe trauma
or thermal injury is associated with an increased complica­
tion rate. Factors that appear to be important in reducing
the incidence of a prolonged inflammatory state include
adequate fluid resuscitation within the first 24 hours after
injury, aggressive excision of necrotic tissue, and enteral
feeding.14–16 A third factor is the adaptive capacity of the
host. Results of several studies have shown that extremes
of age and the presence of coexisting disease will diminish
the adaptive capacity of the host and predict a worse prog­
nosis for any given severity of injury.17,18 As noted earlier in
this chapter, the actual contribution of SIRS to the patho­
genesis of sepsis and other forms of systemic injury are in
question.8
The Initiating Event
The crucial pathophysiologic event that precipitates sys­
temic inflammation is tissue damage. This can occur both
as a result of direct injury to tissues from mechanical or
thermal trauma and as a result of cellular injury induced
by ischemia and reperfusion. Injury results in the acute
release of pro-inflammatory cytokines such as tumor necro­
sis factor-α (TNF-α), interleukin (IL)-1, and IL-6. If injury
response to injury, and the presence of organ dysfunction.
The participants proposed that this model could be used to
generate more specific criteria for defining the SIRS phe­
nomenon. Although the validity of this approach remains
to be established, Rubulotta recently reported that the PIRO
criteria have predictive value regarding mortality in septic
patients.5 More recent studies have also validated the PIRO
model. Macdonald and colleagues reported that the PIRO
model performed better than SOFA or MEDS scores in pre­
dicting mortality in patients presenting to the emergency
room with severe sepsis or septic shock.6 Some practitioners
advocate for the validity and value of the PIRO system, but
the system is not widely used in clinical practice.7
Although inflammation is certainly present in patients
with burn injuries, sepsis, and other severe injuries, the
contribution of SIRS to the pathogenesis of those condi­
tions is under question. The most recent consensus confer­
ence assembled to define clinical criteria for sepsis dropped
SIRS from the defining criteria.8 The conference partici­
pants defined sepsis as “life threatening organ dysfunction
due to a dysregulated host response to infection” and noted
that SIRS criteria have poor predictive validity among
patients who are infected.
Another pitfall in the designation of SIRS is the difficulty
of applying the initial criteria to children. Some of the cri­
teria, particularly those for heart and respiratory rates, fall
within the normal physiologic range for young children. In
2002, a consensus conference was assembled to define cri­
teria for sepsis and SIRS in children.9 The participants
defined six age groups based on clinical and physiological
characteristics (Table 19.1). SIRS was defined as the pres­
ence of at least two of the following four criteria, one of
which must be abnormal temperature or leukocyte count:
■ temperature of greater than 38.5°C or less than 36°C;
■ tachycardia, defined as a mean heart rate of greater
than 2 SD above normal for age or for children younger
than 1 year;
■ bradycardia, defined as a heart rate of less than 10%
of normal for age;
■ mean respiratory rate of greater than 2 SD above
normal for age or requirement for mechanical
ventilation;
■ leukocyte count elevated or depressed for age.
Severe sepsis was defined as sepsis plus one of the follow­
ing: cardiovascular dysfunction, acute respiratory distress
syndrome, or two or more organ dysfunctions (respiratory,
renal, neurologic, hematologic, or hepatic).
The definition of septic shock is problematic in children
because children can maintain blood pressure until they
become severely ill. Therefore hypotension is not a useful
criterion for diagnosing shock in children. This group pro­
posed criteria for septic shock that included the presence of
Table 19.1  Pediatric Age Groups for SIRS Criteria
Newborn 0 day to 1 week
Neonate 1 week to 1 month
Infant 1 month to 1 year
Toddler or preschool 2 to 5 years
School age 6 to 12 years
Adolescent 13 to 18 years

19  •  The Systemic Inflammatory Response Syndrome
207
same TLRs that are activated by microbial products. Among
the proposed endogenous TLR ligands are heat shock pro­
teins (recognized by TLR4 and TLR2), high-mobility group
box 1 (HMGB1; recognized by TLRs 4 and 2), histones (rec­
ognized by TLR4), and mitochondrial DNA (recognized by
TLR9).20–22 Activation of TLR signaling pathways results in
the transcription of genes associated with inflammatory
responses. A second sensing system is comprised of cyto­
plasmic NOD-like receptors (NLRs) that sense endogenous
and exogenous ligands during loss of cellular compartmen­
talization or membrane integrity and cause activation of
inflammasomes (Fig. 19.3).23 DAMPs that activate NLRs,
either directly or via adapter molecules, include uric acid,
endogenous DNA, and adenosine triphosphate (ATP).22
Inflammasome assembly ultimately results in activation of
inflammatory caspases such as caspase-1. Activated
caspase-1, also known as IL-1-converting enzyme, causes
cleavage of pro-IL-1 and pro-IL-18 into active mature pro­
teins. The IL-1 and IL-18 produced by this interaction are
released from cells and facilitate the pro-inflammatory
response.
SIRS and Immunological
Perturbations
Inflammatory responses are important for the early ini­
tiation of tissue repair and activation of innate immune
cells in response to local infection. Cytokines such as IL-6,
TNF-α, and IL-1 recruit and activate macrophages and
neutrophils at sites of infection. To prevent tissue damage
caused by prolonged or excessive inflammation, local anti-
inflammatory responses are initiated to resolve the early
is severe, as in extensive thermal injury, a profound release
of cytokines and noncytokine mediators of inflammation
occurs, resulting in the induction of a systemic inflamma­
tory reaction. The ability of the host to adapt to this sys­
temic inflammatory response depends on the magnitude
and duration of the response as well as the adaptive capac­
ity of the host. If the insult and the host’s response to it are
beyond the adaptive capacity of the host, or if adequate
resuscitation is not promptly initiated, organ injury may
ensue during the early post-injury period. Factors that have
been implicated in the worsening or prolongation of SIRS
include inadequate resuscitation during the acute phase
following thermal injury, persistent or intermittent infec­
tion, ongoing tissue necrosis, and translocation of bacteria
or endotoxin across the bowel.18,19
The actual mechanisms that initiate trauma-induced
inflammation at the cellular and molecular levels are
becoming increasingly understood. Two primary sensing
systems have been identified. Toll-like receptors (TLR)
respond to endogenous cellular factors that are produced or
released following tissue trauma. TLR are expressed by leu­
kocytes and some parenchymal cells. They allow the host to
sense the presence of microbes via pathogen-associated
molecular patterns (PAMPs) and initiate an innate immune
response (Fig. 19.1). TLR also have the ability to respond to
endogenous ligands that are leaked from cells upon their
destruction by burn injury. These molecules are referred to
as damage-associated molecular patterns (DAMPs) and are
typically intracellular molecules with normal cellular func­
tions (Fig. 19.2). As cells are damaged by thermal injury,
these molecules are released into the extracellular matrix.
Due to their normal intracellular localization, these mol­
ecules are recognized as danger signals and can bind to the
Triacyl
lipopeptide
TLR1 TLR2
Inflammatory
cytokines
Inflammatory
cytokines
Type I IFN
Inflammatory
cytokines
Inflammatory
cytokines
Type I IFN
Inflammatory
cytokines
TLR2 TLR6
TLR3
TLR4
TLR7/8
TLR9
TLR5
TLR11
Adapters
TIRAP
MyD88
MyD88
MyD88
Trif
TIRAP
TIRAP
MyD88
MyD88
MyD88
MyD88
Trif
TRAM
Imidazoquinolines
ssRNA
Diacyl
lipopeptide
CpG DNA
Hemozoin
Profilin-like protein
Uropathogenic
bacteria
LPS
dsRNA
Flagellin
Fig. 19.1  Toll-like receptor signaling. Toll-like receptors (TLR) are membrane-associated receptors that recognize microbial products and endogenous
products released during tissue injury, allowing the host to recognize the presence of microbes or tissue injury. TLR activation initiates intracellular
signaling pathways that facilitate transcription of pro-inflammatory gene products. (From Kawai T, Akira S. TLR Signaling. Cell Death Differ. 2006;
13:816–825.)

19  •  The Systemic Inflammatory Response Syndrome
208
associated with adaptive immune responses were down-
regulated at the same time, suggesting impaired effector
functions. The magnitude and duration of these responses
correlated with complications after injury. This is supported
by earlier studies examining levels of pro-inflammatory
IL-6 and anti-inflammatory IL-10 in the circulation of burn
patients.28 Burn patients who eventually developed sepsis
during their acute care had substantially higher levels of
circulating IL-6 and IL-10 as early as 1 day post-burn. Later
development of lethal sepsis was associated with persis­
tently high levels of these cytokines. More recently, a new
model has been proposed to characterize the responses and
outcomes of patients following severe traumatic injury (Fig.
19.4). This model proposes that patients who rapidly resolve
their SIRS and CARS responses return to immune homeo­
stasis and recover from injury without major complica­
tions. However, if SIRS and CARS are not resolved, the
patient develops persistent inflammation, immunosuppres­
sion, and catabolism syndrome (PICS), in which persistent
inflammation and immunosuppression are accompanied by
severe muscle protein catabolism (described in other chap­
ters).29 Secondary nosocomial infections are a risk and can
exacerbate the existing inflammation, leading to multior­
gan failure and death.
The Two-Hit Hypothesis
Some investigators have described a phenomenon in which
the injured host manifests an exaggerated inflammatory
response if confronted with a secondary inflammatory
stimulus during the post-injury period. This phenomenon
has been termed the “two-hit hypothesis.” Although the
pathobiology of the two-hit hypothesis is not completely
understood, monocytes and macrophages appear to play a
inflammatory response. In the case of large burn injuries,
the inflammatory response is massive and becomes systemic.
A compensatory anti-inflammatory response referred to as
the counter anti-inflammatory response syndrome (CARS)
may be mounted in an attempt to restore homeostasis and
control SIRS. Increased production of anti-inflammatory
cytokines such as IL-10 and transforming growth factor-β
(TGFβ) and leukocyte apoptosis are part of this response.24,25
A prolonged or excessive anti-inflammatory response
predisposes the patient to infection. The pathogenesis of
injury-induced immunosuppression is discussed in detail
elsewhere in this book. Nevertheless there is likely great
heterogeneity in the host response to injury and infection.
A recent report by Davenport and colleagues showed that
there is great interindividuality in the peripheral blood tran­
scriptomic response during sepsis but that patients exhibit­
ing a signature reflective of immunosuppression, endotoxin
tolerance, and T-cell exhaustion had a worse prognosis.26
They further noted that the immunosuppressed phenotype
can develop early during sepsis and may render the septic
host unable to adequately mount an adequate response to
clear the primary infection.
Our understanding of these syndromes has evolved to
better describe this response that is shared by burn and
severe non-burn trauma patients. For decades, the host
response to injury-induced systemic inflammation has been
described by the SIRS/CARS paradigm. It was initially
believed that SIRS was resolved during CARS due to mutual
regulatory effects of the mediators associated with the
respective syndromes. However, examination of the tran­
scriptome of leukocytes from trauma patients has revealed
that SIRS and CARS exist simultaneously. Specifically, genes
associated with both inflammatory and anti-inflammatory
pathways were simultaneously up-regulated after injury,
and this was described as a “genomic storm.”27 Genes
Danger signals
Extracellular ATP
Uric acid
IL33
Extracellular
matrix
Mitochondria
Cytoplasm
Nucleus
Cell
P2RX7
NLRP3
ST2
Extracellular ATP
Mitochondrial DNA
EDN
HMGB1
Receptors
HMGB1
TLR
Effects
Immune
activation
S100
Histones
HSP
Fig. 19.2  Damage-associated molecular patterns (DAMPs). DAMPS are typically intracellular molecules with normal cellular functions that serve as
danger signals when released into the extracellular matrix from damaged cells. DAMPs bind to various Toll-like receptors (TLRs) and other pathogen-
associated molecular pattern receptors on leukocytes to activate inflammatory cascades. HMGB1, high mobility group box-1 protein; HSP, heat shock
protein; EDN, eosinophil-derived neurotoxin; IL-33, interleukin-33; TLR, Toll-like receptor; RAGE, receptor for advanced glycation end-products; NLRP3,
NOD-like receptor family, pyrin domain containing 3 (From Fontaine M, Lepape A, Piriou V, Venet F, Friggeri A. Innate danger signals in acute injury: From
bench to bedside. Anaesth Crit Care Pain Med. 2016;35:283–292.)

19  •  The Systemic Inflammatory Response Syndrome
209
small dose, macrophages are triggered to become fully acti­
vated and to secrete large amounts of TNF-α. Studies by
Paterson et al.30 showed that macrophages have increased
responsiveness to ligands for TLR2 and TLR4 following
burn injury. TLR2 and TLR4 play an integral role as com­
ponents of receptor complexes for DAMPs and various
microbial products such as peptidoglycans, lipoproteins,
and lipopolysaccharide. Enhancement of TLR2 and TLR4
responses during the post-injury period may be one mecha­
nism contributing to the two-hit phenomenon.
The exaggerated response to a secondary stimulus seen
in severely injured patients appears to have functional con­
sequences. Several studies that focused on organ injury
caused by systemic inflammatory processes indicate that a
phenomenon comparable to the cellular events just
described can occur in severely injured patients.31 Dehring
et al. found more persistent pulmonary hypertension and
an exaggerated hyperdynamic response to bacteremia in
sheep when a week-old thermal injury preceded systemic
bacterial challenge.32 In a rat model of intestinal ischemia–
reperfusion injury and endotoxemia, lung albumin leak
and mortality rate increased only if both injuries occurred
sequentially.33 Combined administration of low doses of
endotoxin and TNF-α to rats caused hypotension and meta­
bolic effects that are commonly seen after giving a highly
lethal dose of either compound alone.34 These findings are
in keeping with the fact that multiple organ damage usually
develops over a prolonged period during which several
insults might occur. It also emphasizes why it is so impor­
tant to minimize inflammatory insults such as tissue ische­
mia or infection, particularly in patients in whom systemic
inflammation is already present.
Cytokine and Noncytokine
Mediators of SIRS
Several pro-inflammatory cytokines, chemokines, and
noncytokine inflammatory mediators play a role in the
pathogenesis of SIRS. Cytokines comprise a broad group
of polypeptides with varied functions within the immune
response (Table 19.2). The classic mediator of systemic
inflammation is TNF-α. TNF-α is released primarily by
macrophages within minutes of local or systemic injury
and modulates a variety of immunologic and metabolic
events.35 At sites of local infection or inflammation, TNF-α
initiates an immune response that activates antimicrobial
defense mechanisms and, once the infection is eradicated,
tissue repair. It is a potent activator of neutrophils and
mononuclear phagocytes and also serves as a growth factor
for fibroblasts and as an angiogenesis factor. However,
systemic release of TNF-α can precipitate a destructive
cascade of events that can result in tissue injury, organ
dysfunction, and, potentially, death. Among the systemic
effects of TNF-α are the induction of fever, stimulation of
acute-phase protein secretion by the liver, activation of the
coagulation cascade, myocardial suppression, induction of
systemic vasodilators with resultant hypotension, catabo­
lism, and hypoglycemia.35,36 Numerous studies have shown
that administration of TNF-α to experimental animals
will mimic the systemic inflammatory response observed
in sepsis and after severe injury. Another important effect
central role in mediating the process. For example, the lym­
phokine α-interferon (IFN-α), produced during the initial
injury, might act as the first signal and prime macrophages
for a heightened inflammatory response if a second stimu­
lus is encountered. Several changes in macrophage func­
tion, including an increase in the transcription rate of
mRNA for TNF-α, can be induced by exposure to IFN-α.
However, TNF-α protein is not produced in large amounts
in response to the first inflammatory insult. If a second
stimulus, such as endotoxin exposure, is provided in even a
3
1
2
LRR
NACHT
NACHT
PYD
PYD
CARD
CARD
CASP
CASP
CASP
CASP
CARD
CARD
PYD
LRR
PYD
ATP
K+
DAMP/
PAMP
DAMP/PAMP
Crystalline/
particulate
ligands
Lysosomal
rupture
Pannexin-1
Reactive oxygen
species
NLRP3
CASP1
Cathepsin B
inhibitor
(Ca-074-me)
NLRP3 inflammasome
assembly
Activated
Caspase-1
IL-1β
IL-1β
Pro-IL-1β
‘Priming’ by
proinflammatory stimuli,
e.g. TLRs, TNF, IL-1β
ASC
Cytoplasm
Nucleus
P2X7
Fig. 19.3  The inflammasome is an intracellular signaling complex that
is activated by a variety of endogenous and microbial products and
causes activation of inflammatory caspases such as caspase-1. Activa­
tion of this system results in release of interleukin-1 (IL-1) and IL-18
during periods of inflammation. (From Schroder K, Tschopp J. The inflam­
masomes. Cell 2010;140:821–832.)

19  •  The Systemic Inflammatory Response Syndrome
210
IL-1 is released primarily by mononuclear phagocytes, and
its physiologic effects are essentially identical to those of
TNF-α.38 However, important differences exist between the
functions of IL-1 and TNF-α. Most notably, IL-1 does not
induce tissue injury or apoptotic cell death by itself, but can
potentiate the injurious effects of TNF-α. The IL-1 family of
of TNF-α is its ability to induce apoptosis of a variety of
cell types.37 TNF-induced apoptosis may be one mecha­
nism by which it induces tissue injury at high systemic
concentrations.
TNF-α is also a potent stimulus for the release of other
pro-inflammatory mediators, particularly IL-1 and IL-6.
Trauma
SIRS
CARS
Persistent inflammation
Protein catabolism/cachexia
Progressive immunosuppression
Complicated outcomes
Uncomplicated
Chronic low-grade inflammation
Rapid recovery
ICU day 14
Return to homeostatis
Early
MOF
CCI
PICS
Indolent
death
Fulminant death
Innate
immunity
Adaptive
immunity
Fig. 19.4  The SIRS–CARS–PICS model of the systemic response to severe injury. Tissue injury induces the production of pro-inflammatory mediators
resulting in the systemic inflammatory response syndrome (SIRS). A compensatory anti-inflammatory response may be simultaneously mounted in an
attempt to control inflammation, resulting in the counter anti-inflammatory response syndrome (CARS). Patients able to resolve these syndromes
recover whereas persistent perturbations in inflammatory balance may lead to persistent inflammation, immunosuppression, and catabolism syn­
drome (PICS). In this state, patients are susceptible to infection and are at risk for lethal systemic inflammatory responses and severe protein catabolism
that leads to cachexia and, if unresolved, death. (From Vanzant EL, Lopez CM, Ozrazgat-Baslanti T, et al. Persistent inflammation, immunosuppression, and
catabolism syndrome after severe blunt trauma. J Trauma Acute Care Surg. 2014;76:21–30.)
Table 19.2  Cytokine and Chemokine Mediators of Systemic Inflammation
Cytokine
Polypeptide
Size
Cell Source
Cell Target
Primary Effects
Tumor necrosis
factor- α (TNFα)
17 kDa
Monocytes, macrophages, T
lymphocytes
Neutrophil
Endothelial cells
Hypothalamus
Liver
Muscle, fat
Heart
Macrophages
T lymphocytes
Various tissues
Activation (inflammation)
Activation (inflammation/coagulation)
Release of vasodilators (NO)
Fever
Acute-phase response
Catabolism
Myocardial suppression
Release of cytokines, inflammation
Inflammation
Apoptosis?
Interleukin-1 (IL-1)
17 kDa
Monocytes, macrophages
T cells
Endothelial cells
Liver
Hypothalamus
Muscle, fat
Activation (inflammation)
Activation (inflammation/coagulation)
Release of vasodilators (NO)
Acute-phase response
Fever
Catabolism
Interleukin-6 (IL-6)
26 kDa
Monocytes, macrophages, T
cells, endothelial cells
Liver
B cells
Acute-phase response
Activation
Interleukin-8 (IL-8)
10 kDa
Monocytes, macrophages,
endothelial cells
Neutrophils
Chemotaxis, activation
Interferon-γ (IFN-γ)
21–24 kDa
T cells, NK cells
Macrophages
Activation (inflammation)
Interleukin-12 (IL-12)
70 kDa
Macrophages
T cells, B cells, NK cells
Activation, differentiation
Interleukin-18
Macrophages
T cells, NK cells
Activation, differentiation
IL-10
Monocytes/Th2 lymphocytes,
mast cells, regulatory T cells
Macrophages Th1
lymphocytes, NK cells
Inhibition, activation regulation

19  •  The Systemic Inflammatory Response Syndrome
211
NF-κB mobilization. IRF-3 is mobilized through activation
of the Trif-associated signaling pathway and results primar­
ily in transcription of type I interferon (IFN-α) genes. The
STAT1 pathway is induced by activation of type I (IFN-α)
and type II (IFN-γ) receptors. Together these transcription
factors mediate the transcription of numerous factors
involved in inflammation and tissue repair (Fig. 19.6).
proteins, including IL-18, is the only group of cytokines for
which known natural antagonists have been identified. The
IL-1 receptor antagonists (IL-1ra) bind to the IL-1 receptor
but do not induce receptor activation.38 These proteins
appear to function as competitive inhibitors of IL-1 action.
As noted earlier, the systemic release of IL-1 is dependent
on the activation of inflammasomes and caspase-1.23
IL-6 is another protein that is commonly increased in the
circulation of patients with SIRS.38 Macrophages, endothe­
lial cells, and fibroblasts secrete this protein. IL-6 itself does
not induce tissue injury, but its presence in the circulation
has been associated with poor outcome in trauma patients,
probably because it is a marker of ongoing inflammation.
The primary effect of IL-6 is to induce secretion of acute-
phase proteins from the liver as well as to serve as a growth
and differentiation factor for B lymphocytes.
Interferon-γ (IFN-γ) is a cytokine that facilitates the
amplification of the acute inflammatory response, particu­
larly the stimulation of cytokine secretion, phagocytosis,
and respiratory burst activity by macrophages. IFN-γ is
secreted primarily by T lymphocytes and natural killer (NK)
cells in response to antigen presentation, as well as by
macrophage-derived cytokines such as IL-12 and IL-18.
The primary effect of IFN-γ is to amplify the inflammatory
response of macrophages. In response to IFN-γ, the phago­
cytic and respiratory burst activities of macrophages are
increased, secretion of inflammatory mediators such as
TNF-α and IL-1 is enhanced, and antigen presentation is
potentiated by upregulation of class II major histocompat­
ibility complex. Blockade of IFN-γ production or function
has been shown to markedly reduce the deleterious inflam­
matory effects induced by bacterial endotoxin.39 Therefore
IFN-γ is believed to be an important factor in the amplifica­
tion of SIRS.
Chemokines are a family of proteins that function pri­
marily as chemotactic factors for leukocytes and, when pro­
duced inappropriately or in excess, can contribute to
damaging systemic or local inflammation (Table 19.3). IL-8
is the most widely studied chemokine in the setting of sepsis
and SIRS; it is a potent chemoattractant for neutrophils and
is a major factor in recruiting neutrophils to inflammatory
foci. Several studies have shown that IL-8 plays a role in
mediating tissue injury in the setting of trauma and burn
injury, particularly in the lung.40,41
Production of most soluble mediators of inflammation is
regulated at the transcriptional level. Some of the key tran­
scription factors that control pro-inflammatory gene expres­
sion include nuclear factor-κB (NF-κB), AP-1, and IRF-3
(Fig. 19.5). NF-κB is composed of a family of proteins
including p50 (NF-κB1), p65 (RelA), C-Rel, and p52 (NF-
κB2) that combine to form homo- or heterodimers and ulti­
mately function to regulate the transcription of a variety of
cytokine, chemokine, adhesion molecule, and enzyme
genes involved in SIRS.42 Increased translocation of NF-κB
has been associated with a poor outcome in some studies.
Activation of NF-κB in peripheral blood monocytes corre­
lates with increased mortality in septic patients, and alveo­
lar macrophages from patients with adult respiratory
distress syndrome (ARDS) exhibited higher nuclear NF-κB
levels than critically ill patients without ARDS.43,44 The
AP-1 complex is activated through activation of MAP
kinases by stimuli that are similar to those required for
Table 19.3  Classification of Chemokines
Chemokine Type
Target Cell
CXC CHEMOKINES
CXCL8 (IL-8, mouse MIP-2)
Neutrophils
CXCL1 (GROα, mouse KC)
Neutrophils
CXCL2 (GROβ, mouse KC)
Neutrophils
CXCL3 (GROγ, mouse KC)
Neutrophils
CXCL5 (ENA-78)
Neutrophils
CXCL6 (GCP-2)
Neutrophils
CXCL4 (PF4)
Fibroblasts, stem cells
CXCL9 (Mig)
T and NK cells
CXCL10 (IP-10)
T and NK cells
CXCL11 (I-TAC)
T and NK cells
CXCL12 (SDF-1α/β)
T lymphocytes
CC CHEMOKINES
CCL3 (MIP-1α)
Monocyte/macrophages, T and B cells,
NK cells, basophils
CCL4 (MIP-1β)
Same as above
CCL22 (MDC)
Monocyte, T lymphocytes
CCL25 (TECK)
Macrophages, T lymphocytes
CCL17 (TARC)
T lymphocytes
CCL5 (RANTES)
Monocyte/macrophages, T/NK cells
BASOPHILS
CCL14 (HCC-1)
Monocytes
CCL16 (HCC-4)
Monocytes, lymphocytes
CCL18 (DC-CK-1)
T lymphocytes
CCL20 (MIP-3α)
T lymphocytes
CCL19 (MIP-3β)
T lymphocytes
CCL2 (MCP-1)
T lymphocytes, monocytes,
CCL8 (MCP-2)
Same as above
CCL7 (MCP-3)
Same as above
CCL13 (MCP-4)
Same as above
CCL11 (Eotaxin)
Eosinophils
OTHER CHEMOKINES
XCL1 (Lymphotactin)
T lymphocytes, NK cells
CX3CL1 (Fractalkine)
T lymphocytes, monocytes
The current conventional names of chemokines are presented and original
names are provided in parentheses for reference.

19  •  The Systemic Inflammatory Response Syndrome
212
(Fig. 19.7). However, in SIRS, excessive complement acti­
vation appears to cause significant cellular injury in the
host. Products of the complement cascade, most notably
C3a and C5a, are potent activators of inflammation and
leukocyte chemotaxis.48 C3a and C5a also directly acti­
vate neutrophils and promote release of reactive oxygen
intermediates and proteases. Excessive release of these
factors can result in significant tissue injury. The mem­
brane attack complex (MAC) is the terminal component of
the complement cascade. MAC results from the aggrega­
tion of the complement components C5–C9 on biological
membranes. The accumulation of MAC on cell surfaces can
result in significant tissue and cellular injury and may be
a major factor in the pathogenesis of MODS. Suber and
colleagues49 have reported that complement-mediated
responses to self-antigens exacerbate tissue injury after burn
injury.
Several noncytokine factors have been implicated in the
pathogenesis of SIRS. Platelet-activating factor (PAF) is a
phospholipid autocoid released by endothelial cells that
regulates the release of cytokines and amplifies the pro-
inflammatory response. It appears to be an important factor
in the adhesion of neutrophils to endothelial cells. The pro­
longed presence of PAF in the serum of patients with SIRS
has correlated with poor outcome.45 Eicosanoids are arachi­
donic acid metabolites that regulate many aspects of the
immune response. Leukotrienes (LTC4–LTE4) induce con­
traction of endothelial cells and encourage capillary
leakage.46 Thromboxane A2, a macrophage- and platelet-
derived factor, promotes platelet aggregation, vasoconstric­
tion and, potentially, tissue thrombosis.47
The complement cascade is composed of more than
30 proteins that interact in a complex fashion to mediate
inflammation and direct lysis of microbes and other cells
TIRAP/Mal
IRAK4
MyD88
Trif
TRAM
Cytoplasm
Nucleus
Endosome
TLR3
TLR4
TRAF6
TBK1
IKKi
IRF3
IRF3
RIP1
TRAF6
UB
TAB1/2/3
P
P
P
P
UB
TAK1
MAPKs
AP-1
Type 1 IFN
Inflammatory cytokines
IKKγ
IκBs
NF-κB
NF-κB
IKKαβ
Degradation
Fig. 19.5  Major inflammation-associated transcription factors include nuclear factor-κB (NF- κB), AP-1, and IRF-3. Activation of these pathways is medi­
ated through MyD88- and Trif-dependent signaling after Toll-like receptor ligation. (From Kawai T, Akira S. TLR Signaling. Cell Death Differ.
2006;13:816–825.)

19  •  The Systemic Inflammatory Response Syndrome
213
markers in patients with SIRS or sepsis. This approach
seems logical based on the observation that circulating
cytokines have been observed in several clinical studies of
trauma, sepsis, and thermal injury. Given its central role in
the activation and regulation of the pro-inflammatory
response, TNF-α has been studied extensively as a plasma
marker of SIRS. The results have been inconsistent. Martin
et al.50 showed that TNF-α levels were markedly elevated in
patients with septic shock and correlated with fatal outcome.
However, their results also showed that trauma patients did
not exhibit the same marked elevations in circulating TNF-
α, nor did circulating TNF-α concentrations correlate with
increased mortality in trauma patients. In some published
studies, measurement of circulating TNF-α levels in burn
patients has not provided a useful marker of outcome.51,52
Overall, plasma TNF-α levels have been variable and incon­
sistent and have not correlated with mortality or the devel­
opment of MODS. However a study by Zhang et al.53 in 25
patients with greater than 30% total body surface area
(TBSA) burns demonstrated marked increases in plasma
TNF-α levels and a significant correlation between TNF-α
concentration and shock, MODS, and death. These findings
support the results of Marano et al.,54 who showed a signifi­
cant correlation between circulating TNF-α concentration
and mortality in burned patients. Therefore, taken together,
these results show that TNF-α could serve as a useful marker
of ongoing inflammation as well as an indicator of morbid­
ity and mortality in the setting of burn injury, but contro­
versy remains.
TNF-α interacts with two known cell surface receptors
designated tumor necrosis factor receptor (TNFR)-I and
TNFR-II. TNFR-I, also known as TNF-R55 or p55, is
expressed on a variety of cells and its activation mediates
most of the activities of TNF-α, including induction of
apoptosis. Activation of TNFR-II (TNF-R75 or p75) results
Circulating Cytokines as
Markers of SIRS and Predictors
of Outcome
Numerous studies have been undertaken with the goal of
using plasma cytokine levels as diagnostic and prognostic
AP-1, NF-κB
transcription factors
Active STAT1
transcription factor
Stimulation of gene expression
Phagocyte
oxidase
iNOS
Tissue
factor
Cytokines
(TNF,
IL-12)
Increased MHC
molecules,
costimulators
Enhanced
antigen
presentation
Inflammation,
metabolic
alterations
Tissue
remodeling
and repair
Coagulation
Nitric
oxide
Reactive
oxygen
species
Killing of
microbes
Growth factors
Angiogenic factors
Metalloproteinases
Fig. 19.6  Regulation of pro-inflammatory gene expression. Inflammatory stimuli induce activation of transcriptional pathways mediated by nuclear
factor-κB (NF-κB), AP-1, and STAT1 that result in production of pro-inflammatory mediators. (From Cotran R, Kumar V, Collins T, eds., Robbins pathologic
basis of disease, 6th edn. Philadelphia: WB Saunders; 1999:75.)
Antigen/antibody
complexes
(adaptive)
Microorganisms
Alternative
pathway
(innate)
Classic
pathway
Lectin
pathway
C3
C3b
C5a
C5-C9
terminal sequences
Membrane attack
complex (MAC)
C3a
C3a and C5a (anaphylactotoxins): increase vascular permeability,
chemotactic factors, opsonins
Fig. 19.7  The complement system can be activated by three primary
mechanisms and facilitates the amplification of innate and acquired
immune responses as well as directly mediating microbial lysis. The
primary functions of complement are opsonization, leukocyte chemo­
taxis, and direct killing of microbes. (From Abbas AK and Lichtman AH,
Cellular and molecular immunology, 5th edn., Saunders).

19  •  The Systemic Inflammatory Response Syndrome
214
of systemic infections. Although blood cultures provide
important information regarding the presence of infection
and the identity of the infecting organism, it can often take
several days to obtain reliable results, and the presence of
negative cultures does not assure the absence of infection.
Therefore efforts have been made to identify other markers
of systemic infection. The two markers that have been most
consistently elevated in patients with infection are procal­
citonin and CRP. Studies have shown that increased plasma
levels of procalcitonin or CRP are sensitive markers of sys­
temic infection.62 Both of these markers have been shown
to be more reliable than clinical signs in the diagnosis of
infection in high-risk surgical and trauma patients. Recent
studies show that procalcitonin and CRP can be used to
distinguish patients with systemic infection from those with
noninfectious systemic inflammatory processes.63–65
Overall several markers of inflammation and infection
have been identified in burn and trauma patients. Some of
these have been shown to be consistent indicators of injury
severity. However, cytokine and noncytokine markers of
inflammation are not used routinely in the laboratory eval­
uation of burned patients. With further research and dem­
onstration of the reliability of these markers, they may
become an accepted part of clinical practice. In addition,
technology is evolving to measure these markers in a rapid
and cost-effective manner, which may allow blood cytokine
markers to become a component of patient management in
the future.
Anti-Inflammatory Therapy
for SIRS
Despite our increased understanding of the role of inflam­
matory mediators in the pathogenesis of SIRS and sepsis,
most anti-inflammatory drug regimens have had little
success in the treatment of this problem. Neutralizing
approaches to several inflammatory mediators have been
studied. All of these studies have demonstrated, at best,
marginal improvement in septic morbidity and mortality.
None of the direct anti-inflammatory strategies has been
successfully employed to minimize burn-associated inflam­
mation. One of the most widely studied approaches for the
treatment of SIRS is the use of monoclonal antibodies to
TNF-α. Several multicenter, prospective clinical trials were
undertaken in septic patients using several different anti­
bodies to TNF-α.66,67 Those studies did not demonstrate
improved outcome in patients receiving anti-TNF-α com­
pared to placebo. One study evaluated the efficacy of a
chimeric antibody to TNF in patients with severe sepsis.67
Circulating levels of TNF-α as well as a variety of other
inflammatory mediators were assessed. Although circulat­
ing levels of TNF-α were transiently decreased, anti-TNF-α
therapy did not result in reduction of circulating levels of
other inflammatory mediators such as IL-1β, IL-1ra, sTNFR,
or IL-6. In addition, evidence of systemic inflammation
was not reduced and overall mortality was not improved
in anti-TNF-α-treated patients. Similarly, the use of sTNFR
as a strategy to neutralize the systemic effects of TNF-α
and reduce sepsis-associated morbidity and mortality was
unsuccessful.68 Other anti-inflammatory approaches that
have been studied and found to be largely ineffective include
in cellular proliferation and activation. During inflamma­
tory states, TNFR are released from cells and may serve as
antagonists of TNF-α. Several investigators have character­
ized surface-bound and soluble TNFR (sTNFR) in sepsis and
trauma.53,55,56 Hubl et al.55 showed that surface TNFR-I was
up-regulated, whereas TNFR-II was down-regulated in
patients with SIRS. Increased TNFR-I correlated with
increased body temperature but not with survival. SIRS
patients with decreased surface TNFR-II had a trend toward
increased mortality. A study by Zhang et al.53 showed a
higher incidence of shock, MODS, and mortality in burn
patients with increased plasma sTNFR-I and sTNFR-II
levels. Presterl et al.56 showed a correlation between sTNFR
and APACHE III scores, as well as the incidence of shock
and mortality in septic patients. Sikora and colleagues57
have reported increased concentrations of sTNFR-I and
sTNFR-II in the plasma of burned children. sTNFR concen­
trations correlated with burn surface area and decreased
with adequate treatment. Children with hypovolemic shock
had higher plasma concentrations of sTNFR. Overall, in the
studies published to date, the presence of high levels of
circulating sTNFR correlates with ongoing inflammation
and may serve as an indicator of poor prognosis.
Another family of proteins that has been extensively ana­
lyzed as markers of SIRS is IL-1 and IL-1ra. In burn patients,
low IL-1ra levels correlated with mortality in two indepen­
dent studies.58,59 Plasma IL-1ra levels have been shown to
correlate with body surface area burned, extent of third-
degree burn, and the presence of inhalational injury, both
in adults and children.52,57,58
Recently, IL-8 has been reported as a predictor of poor
outcome in burn patients.60 In burn patients with lower
levels of IL-8 (<234 pg/mL), IL-8 levels were predictive for
multiorgan failure and correlated with the size of the burn
injury. In burn patients with high levels (>234 pg/mL), IL-8
was predictive for the development of sepsis and mortality.
Of the cytokine markers studied to date, elevated levels
of IL-6 appear to be one of the more consistent markers of
poor outcome in burn, trauma, and septic patients. One of
the known functions of IL-6 is induction of acute-phase
proteins such as CRP by the liver. In some studies, CRP has
been shown to parallel IL-6 as a marker of increased mor­
tality.59 Although IL-6 itself does not appear to have any
known direct injurious effects, it apparently serves as a con­
sistent marker of ongoing inflammation. Elevated plasma
IL-6 levels have correlated with increased mortality in
experimental and clinical studies of thermal injury, sepsis,
trauma, and hemorrhagic shock.51,61 A study by Taniguchi
et al.61 showed that an increased ratio of IL-6 to the anti-
inflammatory cytokine IL-10 was a predictor of poor
outcome in patients with SIRS.
In trauma and burn patients it is often difficult to differ­
entiate whether SIRS is a result of the injury itself or due
to superimposed infection. Most of the clinical signs of sys­
temic infection, such as fever and leukocytosis, are by defi­
nition present in SIRS. Therefore considerable attention has
been placed on identifying indirect markers of systemic
infection that could serve to differentiate SIRS caused by
infection from that caused by trauma. It is important clini­
cally to identify patients with systemic infection in order to
initiate antibiotic therapy in a timely fashion. Additionally
positive blood cultures are the gold standard for diagnosis

19  •  The Systemic Inflammatory Response Syndrome
215
circulation for days. Administration of anti-HMGB-1 to
septic mice has been shown to improve survival. Conversely
systemic administration of HMGB-1 to mice is lethal.
Whether HMGB-1 plays an important role in inflammatory
injury in humans remains to be determined. However the
concept of late mediators of inflammatory tissue injury
may improve our understanding of the pathophysiology of
SIRS.
As discussed earlier, factors that appear to be important
in limiting the extent of SIRS and, in many cases, reducing
the incidence of shock and MODS are appropriate fluid
resuscitation, hemodynamic support, treatment of infec­
tion with antibiotics, excision of necrotic tissue, and ade­
quate nutritional support.83 There is controversy regarding
the ideal fluid for volume resuscitation in trauma and burn
patients. However, recent studies show that hypertonic
saline has beneficial effects in modulating the SIRS-
associated immunological cascade as well as in restoring
hemodynamic parameters and microcirculatory flow. The
effect of hypertonic saline on immune function has largely
centered on attenuation of post-injury immunosuppres­
sion. Recent studies have shown that resuscitation with
hypertonic saline will improve macrophage and T-cell func­
tion as well as increase resistance to infection in experimen­
tal models of trauma and hemorrhage.84,85 However, the
use of hypertonic fluids has not gained widespread support
in burn resuscitation because of the risk of hypernatremia
and associated complications. Proper nutritional support is
also an important factor in the treatment of severely injured
patients. Enteral feeding formulas supplemented with glu­
tamine, arginine, omega-3 fatty acids, and nucleotides have
been shown to improve outcome in trauma patients.86
Overall, trauma patients receiving immune-enhancing
diets have been shown to have fewer infectious complica­
tions. In general, enteral feeding has been shown to main­
tain gut integrity and improve outcome in burn patients.
Tracey and colleagues have described a cholinergic anti-
inflammatory pathway that may be important in the regu­
lation of inflammation and could be exploited for therapeutic
benefit.87,88 As described, local inflammation activates affer­
ent fibers of the vagus nerve that signal the brain to elicit
an anti-inflammatory response through efferent vagal
fibers (Fig. 19.8). Acetylcholine released by the vagus inter­
acts with α7 nicotinic acetylcholine receptors (α7 nAChR)
on macrophages and suppresses the production of pro-
inflammatory mediators. Those investigators have shown
that electrical stimulation of the vagus nerve will attenuate
the pro-inflammatory response induced by cecal ligation
and puncture or endotoxin challenge. Acetylcholine has
also been shown to inhibit the release of pro-inflammatory
cytokines by cultured macrophages following endotoxin
challenge.87,88 More specific α7 nAChR agonists are under
investigation for the treatment of hyperinflammatory
states, and the possibility of exploiting the cholinergic anti-
inflammatory pathway for therapeutic benefit remains to be
established.
ACTIVATION OF THE COAGULATION CASCADE
DURING INFLAMMATION
Inflammation and coagulation are intimately intertwined.
The coagulation cascade is activated during both tissue
the use of IL-1ra,69,70 anti-bradykinin,71 PAFra,72,73 and
ibuprofen.74,75
Because of the relative ineffectiveness of anti-
inflammatory therapy aimed at neutralizing single media­
tors, more broad-based strategies were developed with the
goal of simultaneously neutralizing, removing, or inhibit­
ing the production of numerous inflammatory mediators.
Hemofiltration was one approach that received consider­
able attention. Several studies have shown that hemofiltra­
tion will increase the clearance of inflammatory mediators,
particularly IL-6, from blood in patients with sepsis.76,77
However none of these studies has demonstrated a signifi­
cant reduction in IL-6 plasma levels. A study by Kellum
et al.77 showed that continuous venovenous hemofiltration
(CVVH) reduced plasma TNF-α concentrations by 13%, and
the use of continuous venovenous hemodialysis (CVVHD)
resulted in a 32% increase in circulating TNF-α levels.
Overall the use of hemofiltration has been largely ineffective
in removing significant amounts of inflammatory media­
tors from the blood of patients with sepsis, and there is
currently no evidence that this approach will reduce mor­
bidity and mortality.
The use of glucocorticoids in the treatment of sepsis has
been proposed for more than 30 years. A meta-analysis78 of
studies using high-dose glucocorticoids in the treatment of
sepsis was published in 1995 and later summarized by Zeni
and colleagues.79 Overall the use of high-dose glucocorti­
coids to treat sepsis and septic shock has not been beneficial.
In many studies, the use of glucocorticoids in septic patients
was associated with increased mortality. In burned patients
there is no evidence that administration of glucocorticoids
provides effective treatment for systemic inflammation.
More recent studies show that replacement dose steroids
will improve survival in septic patients who have adrenal
insufficiency.80 Recent guidelines from the Surviving Sepsis
Campaign advocate the use of replacement dose glucocor­
ticoids in septic patients refractory to conventional
management.81
The failure of anti-inflammatory approaches to improve
outcome in patients with severe sepsis or septic shock is
likely to be multifactorial. First, the inflammatory response
to injury and sepsis is induced by a complex array of media­
tors that are largely interrelated and have significant redun­
dancy. Therefore, blocking or neutralizing a single mediator
is not likely to have a marked effect on the overall response.
Second, the same mediators that are important in inducing
tissue injury also play an important role in antimicrobial
immunity, and blockade of these mediators may leave the
host more susceptible to subsequent infection. Third, many
of the mediators, particularly TNF-α and IL-1β, are released
within minutes of injury and mobilize the inflammatory
cascade shortly thereafter. Therefore, by the time that signs
of SIRS or sepsis are apparent, many of the injurious effects
of the inflammatory response have already been set in
motion, making therapy ineffective. A recent emphasis has
been placed on the identification of late mediators of inflam­
matory injury. This search has been prompted by the obser­
vation that SIRS- and sepsis-associated death occur days
after the peak effect of inflammatory cytokines. One poten­
tial late mediator that has recently been identified is
HMGB-1.82 HMGB-1 is released by macrophages up to 8 h
after lipopolysaccharide (LPS) challenge and persists in the

19  •  The Systemic Inflammatory Response Syndrome
216
Activated Hageman factor triggers a cascade of proteins to
become activated, resulting in the formation of thrombin.
The intrinsic pathway is most commonly activated by direct
tissue trauma. In contrast, the extrinsic pathway is initiated
by the production of tissue factor. Recent studies indicate
that the extrinsic pathway is the primary coagulation
pathway activated during infection and systemic inflamma­
tion, particularly during sepsis and SIRS.89 Tissue factor is
expressed on tissue surfaces that are not normally exposed
to the vascular compartment, such as subcutaneous tissues
and the adventitial layer of blood vessels. In addition, endo­
thelial cells and activated monocytes produce tissue factor
during periods of inflammation in response to TNF-α, IL-1,
IL-6, and CRP.90 The presence of tissue factor causes activa­
tion of factor VII, which then forms a complex with tissue
factor and ultimately causes the formation of thrombin by
the activation of a series of coagulation factors (Fig. 19.9).
Activation of the coagulation cascade is not only important
in the formation of fibrin clots but also has important effects
on the pro-inflammatory response. Factor Xa, thrombin,
and the tissue factor-VIIa complex have been shown to elicit
pro-inflammatory activity. Specifically, thrombin and the
tissue factor-VIIa complex can induce production of pro-
inflammatory cytokines such as TNF-α by mononuclear
and endothelial cells.89 That effect appears to be mediated
by the binding of these factors to protease-activated recep­
tors on the surface of target cells. Therefore acute inflam­
mation causes activation of the coagulation cascade, which
can then further potentiate the inflammatory response.
Activation of the clotting cascade during inflammation is
limited by several factors. This is important because it pre­
vents uncontrolled induction of procoagulant mechanisms.
injury and infection. It is divided into two pathways that
converge and ultimately cause the activation of thrombin,
with subsequent cleavage of fibrinogen into fibrin (Fig.
19.9). The intrinsic pathway is a series of plasma proteins
that are activated by Hageman factor (factor XII), a protein
synthesized in the liver that is activated by binding to
collagen, basement membrane, or activated platelets.
Central or
‘pharmacological’
vagus nerve stimulators
Liver
Brain
Electrical
vagus nerve
stimulator
TNF
Spleen
Macrophage
α7 agonists
α7 nAChR
α7 subunit
acetylcholine
receptor
Cholinergic
anti-inflammatory
pathway
Nucleus
Cholinergic
agonist
Jak-STAT
anti-inflammatory
pathway
Cytokine
receptor
↑SOCS3
↑Gene
transcription
NF-κB
↓NF-κB
transcription
Jak
Jak
ACh
Vagus nerve
stimulation
Anti-inflammatory
P
P
P
P
–
STAT3
STAT3
STAT3
STAT3
Fig. 19.8  The cholinergic anti-inflammatory pathway. Tissue inflammation sends afferent signals to the central nervous system, resulting in activation
of the cholinergic anti-inflammatory pathway. Release of acetylcholine by the vagus nerve induces anti-inflammatory effects by binding to nicotinic
receptors on the surface of leukocytes. (Adapted from Czura CJ and Tracey KJ. Automatic neural regulation of immunity. J Int Med. 2005;257:156–166; Metz
CN, Tracey KJ. It takes nerve to dampen inflammation. Nat Immunol. 2005;6(8):756–757; Pavlov et al. Crit Care Med. 2007;35:1139.)
Macrophage/
monocyte
Tissue factor
Intrinsic
pathway
VIIa
VIIIa
IXa
Degradation
of Va and VIIIa
Binds TF-VIIa
complex
Binds thrombin
Fibrin clot
Macrophage/
monocyte
activation
Xa
Va
+
Activated
protein C
Tissue factor
pathway
inhibitor
Antithrombin
III
Endothelial
cell
TNFα
IL-1
Thrombin
Fig. 19.9  Regulation of the coagulation cascade during inflammation.
Inflammation primarily causes activation of the extrinsic coagulation
pathway.

19  •  The Systemic Inflammatory Response Syndrome
217
Inhibition of tissue factor function inhibits activation of the
extrinsic clotting pathway during inflammation. Infusion
of TFPI has also been shown to reduce pro-inflammatory
cytokine production during endotoxin infusion in baboons
but not in humans.
THE HEMODYNAMIC RESPONSE
The full clinical picture of systemic inflammation after
thermal injury is characterized by two primary phases.
After the initial injury, inflammation leads to increased vas­
cular permeability and the exudation of protein-rich fluid
from the vascular compartment to the interstitium. This
early fluid leak results in intravascular hypovolemia and
interstitial edema formation. If the patient is adequately
resuscitated, a hyperdynamic phase will ensue that is char­
acterized by a low systemic vascular resistance and high
cardiac output. Patients who are not well resuscitated or
whose cardiac function is compromised may not be able to
increase their cardiac output to the extent needed to main­
tain arterial blood pressure during states of extensive vaso­
dilatation and so might exhibit tissue hypoperfusion and
shock. A reduced vascular responsiveness to vasoconstric­
tors may inhibit successful pharmacologic intervention,
and patients could develop irreversible shock. An intrave­
nous bolus injection of 4 ng/kg endotoxin into healthy vol­
unteers mimics some aspects of the hemodynamic response
seen in septic patients and adequately resuscitated burn
victims.99,100 The low systemic vascular resistance and the
elevated cardiac output can also be induced in animal
models by continuous infusion of low-dose endotoxin101 or
bacteria.102,103
Changes in Endothelial
Permeability
Burn injury, trauma, and sepsis increase microvascular per­
meability in both the systemic104 and the pulmonary
The best-defined factors are antithrombin, the protein C
system, and the tissue factor pathway inhibitor. Anti­
thrombin is produced in the liver and directly binds to
and inactivates thrombin.91 The binding of antithrombin
to thrombin is greatly potentiated by heparin and by gly­
cosaminoglycans present on the endothelial cell surface. In
rodents interaction of antithrombin with the endothelial
cell surface promotes the release of PGI2, which inhibits
TNF-α production by monocytes through the inhibition of
transcription factor NF-κB activation.92 Thus antithrombin
may have anti-inflammatory properties in addition to its
function in regulating coagulation.
Protein C is a circulating protein that is activated by
the thrombin–thrombomodulin complex on the surface
of endothelial cells (Fig. 19.10). Activation of protein C
decelerates the clotting cascade by inactivating factors
Va and VIIIa. Activated protein C (APC) also inhibits
thrombin-induced production of TNF-α by monocytes by
inhibiting the activation of transcription factors NF-κB and
AP-1.93 Therefore APC has both anticoagulant and anti-
inflammatory properties. During sepsis, APC levels can
become depleted due to consumption and inflammation-
induced down-regulation of thrombomodulin. This results
in unchecked formation of thrombin, causing accelerated
coagulation and increased pro-inflammatory activity. The
importance of protein C in regulating thrombin formation
during sepsis is demonstrated by increased mortality in
septic patients with low APC levels.94 Those findings led to
the investigation of APC as an intervention in patients with
sepsis. Early trials showed that APC therapy was effective in
improving survival in patients with severe sepsis.95 However,
further investigation did not demonstrate significant
benefit.96,97
A third important factor in the regulation of thrombin
formation is the tissue factor pathway inhibitor (TFPI). TFPI
is present on the surface of endothelial cells and bound to
lipoproteins in plasma. TFPI inactivates tissue factor by
forming a quaternary complex with tissue factor and factor
VIIa. Factor Xa is the fourth component of the complex.98
Proteolysis of factors Va and VIIIa
Profibrinolysis
Activated protein C Protein C
Cytokine
production
Fibrin clot
formation
Inflammation
Thrombosis
Cytokine
production
Fibrin clot
formation
Induce
Induce
Tissue
factor
Inhibit
Thrombin
Tissue
factor
Thrombin
Thrombomodulin
Endothelium
Normal
Sepsis
Consumption of
protein C
Fig. 19.10  Protein C is a circulating protein that is activated by the thrombin–thrombomodulin complex on the surface of endothelial cells. Activation
of protein C decelerates the clotting cascade by inactivating factors Va and VIIIa. Activated protein C also inhibits thrombin-induced production of
tumor necrosis factor-α (TNFα) by monocytes by inhibiting the activation of transcription factors nuclear factor-κB (NF-κB) and AP-1.

19  •  The Systemic Inflammatory Response Syndrome
218
models of endotoxemia, but it has been generally accepted
that the changes in pulmonary transvascular fluid flux in
phase 2 represent changes in microvascular permeability.
The mechanisms of the increased microvascular permeabil­
ity are still under discussion.
Endothelial cells play an important role in the regulation
of vascular permeability. It has been hypothesized that
endothelial cells can contract upon stimulation.116 As a
result, the intercellular gaps might increase in number
and/or size, establishing the so-called capillary leak syn­
drome. The development of the protein-rich high-
permeability edema can be ameliorated if substances are
administered that raise the endothelial cell content of cyclic
adenosine or guanosine monophosphate.117,118 However,
endothelial cells do not merely serve as targets during sys­
temic inflammation: they actively contribute to the ongoing
inflammatory process. The endothelial cell can be stimu­
lated by endotoxin, TNF-α, or IL-1 to express E-selectin, an
adhesion molecule.119 E-selectin on the surface of endothe­
lial cells interacts with the corresponding L-selectin complex
on polymorphonuclear neutrophils (PMNs) to facilitate
rolling of these cells along the endothelium.120 Moreover
endothelial cells secrete the pro-inflammatory cytokines
TNF-α and IL-1, which activate PMNs. Conflicting data
exist regarding the role of PMNs in SIRS. PMNs are usually
found at the site of tissue injury, to which they migrate
following a concentration gradient of chemotactic stimuli.
Upon stimulation, PMNs roll along endothelial cells, and,
in a further step mediated by PMN CD18/CD11b interac­
tions with endothelial ICAM-1, emigrate from the vessel
into the interstitial space. Antibodies against the common
CD18β chain showed beneficial effects in an animal model
of sepsis-induced lung injury, suggesting that integrin-
mediated PMN emigration is a functionally important
process in the development of acute lung injury.121 On the
other hand, patients who are deficient in CD18 have abun­
dant PMNs in their alveolar spaces, and the monoclonal
antibody 60.3 was ineffective in completely blocking the
migration of PMNs into the lung in a number of condi­
tions.122 We have found that in chronic endotoxemia there
are few PMNs in the lung but numerous macrophages.
Activated PMNs and macrophages release oxygen free radi­
cals and proteases at sites of inflammation. Those processes
appear to be functionally important in the development of
vascular permeability because administration of oxygen
free radical scavengers and antiproteases proved to be
useful in diminishing edema accumulation after endotoxin
challenge.123 However, proteases and oxygen radicals are
also released by macrophages, which are already present
in the tissue, and by monocytes that migrate to sites of
inflammation. Depletion of granulocytes by anti-PMN anti­
serum or by treatment with nitrogen mustard did not
prevent the changes in microvascular permeability follow­
ing the administration of endotoxin.124,125 Moreover
patients deficient in PMNs still develop acute respiratory
distress syndrome (ARDS) associated with sepsis.126,127 On
the other hand, treatment of sheep or goats with hydroxy­
urea, which is another compound used to deplete granu­
locytes, was effective and diminished fluid accumulation in
the lung after endotoxin challenge.128 However, urea scav­
enges free radicals, which might explain its efficacy.129 As
the inflammatory response becomes chronic, many
circulations.105 Increased vascular permeability and cuta­
neous edema are hallmarks of burn shock. The increase in
systemic vascular permeability results in the exudation of
protein-rich fluid from the vascular compartment into the
interstitium. This results in intravascular volume loss and
the concomitant development of interstitial edema. If
resuscitation is not prompt and adequate, this loss in intra­
vascular volume will lead to intravascular hypovolemia,
hypotension, and inadequate tissue perfusion. Severe inter­
stitial edema formation can lead to the development of com­
partment syndrome, with compromise of neurovascular
integrity. The lungs may also be affected. Edema formation
due to an increase in microvascular permeability is a hall­
mark of the acute lung injury. The factors that determine
the transvascular fluid flux are summarized in the Starling-
Landis equation:106,107
J
K
P
P
v
f
mv
i
mv
i
=
−
−
−
[(
)
(
)]
α π
π
where Jv is the transvascular fluid flux, Kf is the filtration
coefficient (measure of the endothelial permeability to small
solutes and water as well as of the permeability surface
area), Pmv is the microvascular hydrostatic pressure, Pi is the
interstitial hydrostatic pressure, α is the osmotic reflection
coefficient to protein, πmv is the microvascular oncotic pres­
sure, and πi is the interstitial oncotic pressure.
Several investigators have studied lymph flow and lymph
protein flux after administration of bacteria or short-time
infusion of 1–2 µg/kg of endotoxin in sheep. Two phases
of permeability change could be distinguished in these
models.108 During phase 1 there was a high microvascular
hydrostatic pressure, as defined by the Gaar equation.109
This was associated with an increase in lung lymph flow,
but the lymph protein concentration was low. It was con­
cluded that the high microvascular hydrostatic pressure
was responsible for the early increase in transvascular fluid
flux. Thromboxane A2 (TXA2) has been found to be respon­
sible for the vasoconstriction that causes local increases
in hydrostatic pressure. Therefore it is not surprising that
administration of the thromboxane synthetase inhibitor
OKY046 prevented the rise in lymph flow during phase
1.110 That effect was also noted after blockage of cyclo­
oxygenase by ibuprofen.111 Early edema formation at the
site of burn injury might be due to a different mechanism.
Data suggest that a marked fall in interstitial hydrostatic
pressure might occur in the injured tissue, which could
explain the immediate onset of edema formation after
thermal injury.112,113 These changes might be the result of
an inhibition of the fibroblast β1-integrin attachment to
collagen.
During phase 2, lymph flow continues to be high.
However, the lymph protein concentration rises consid­
erably and the pulmonary artery pressure is only mildly
elevated.108 The oncotic pressure gradient between micro­
vasculature and interstitial space is reduced during that
period.114 Together these data suggest that the permeability
of the pulmonary endothelium to protein increases in phase
2. In fact, the reflection coefficient for total protein fell from
0.73 to 0.58, with respective changes in the reflection coef­
ficients for albumin (0.66 to 0.5), IgG (0.76 to 0.64), and
IgM (0.91 to 0.83) after 4 hours of Escherichia coli sepsis in
sheep.115 Confirmation of this hypothesis is still pending in

19  •  The Systemic Inflammatory Response Syndrome
219
INCREASED EPITHELIAL PERMEABILITY
Permeability changes during systemic inflammation are
not restricted to the endothelium. Loss of epithelial barrier
function has been noted both in the lung and in the intes­
tine. Administration of 2–4 ng/kg endotoxin to healthy
human volunteers increased their alveolar epithelial perme­
ability to the inhaled 492 Da molecule [99mTc] diethylene­
triamine pentaacetate (DTPA) 3 hours after endotoxin had
been given.100 Human volunteers demonstrated a higher
intestinal epithelial permeability to mannitol/lactulose.140
Bacterial translocation occurred during endotoxemia,141
thermal injury,142 and multiple trauma with hemorrhagic
shock.143 This might well be interpreted as a loss of intes­
tinal barrier function. Nevertheless one must bear in mind
that epithelial permeability to molecules such as lactulose/
mannitol and bacterial translocation do not necessarily
relate to each other. The epithelium could also be injured by
ischemia–reperfusion.144 In addition to changes in vascular
permeability, burn injury also causes marked alterations in
vascular tone and myocardial function that are character­
ized by a variety of temporal alterations.
The Hyperdynamic State
Continuous infusion of endotoxin into sheep and pigs
results in a hyperdynamic circulation.145,146 In addition
to a low systemic vascular resistance and a high cardiac
output with a slightly decreased mean arterial pressure, the
hyperdynamic response is further characterized by hypore­
sponsiveness of isolated vessels to vasoconstrictors and an
increased pulmonary shunt fraction in the presence of a
reduced pulmonary hypoxic vasoconstriction.145,147–149 The
high cardiac output is due to low systemic vascular resis­
tance and increased heart rate.150,151 Paradoxically myo­
cardial function is depressed during sepsis and in severely
burned patients.152,153 The underlying cause of impaired
myocardial function is not fully understood. However,
reports indicate that pro-inflammatory mediators such
as TNF-α, IL-1, IL-6, and nitric oxide (NO) contribute to
this alteration.153,154 The treatment of myocardial function
during sepsis and after burn trauma is an important consid­
eration in overall hemodynamic management. The combi­
nation of myocardial dysfunction and increased pulmonary
vascular resistance is a likely cause of right heart failure in
pediatric burn patients. Treatment options include dobuta­
mine and phosphodiesterase inhibitors such as milrinone.
The Surviving Sepsis Campaign recommends dobutamine
as a first-line agent for treatment of hypotension and hypo­
perfusion in pediatric patients with sepsis, especially when
myocardial dysfunction is present.81
NO has been implicated as a mediator of systemic vasodi­
lation and myocardial depression during sepsis and after
major burn injury. NO can be synthesized from its precursor
L-arginine by three different enzymes (Fig. 19.11). The
calcium-dependent constitutive nitric oxide synthases
(NOS) such as endothelial NOS (eNOS) and neuronal NOS
(nNOS) are responsible for the basal release of NO, which
seems to play an important role in the regulation of vascu­
lar tone under physiologic conditions. In vitro data suggest
that these enzymes might become inactivated early after
mediators have been released and more than one mecha­
nism may be responsible for capillary leak.
The role of arachidonic acid metabolites in facilitating
increased vascular permeability has been extensively inves­
tigated. Administration of the thromboxane synthetase
inhibitor OKY046 not only reduced transvascular fluid flux
in phase 1, but was also effective in phase 2 after endotoxin
challenge.110 This finding suggests that thromboxanes par­
ticipate in permeability alterations during systemic inflam­
mation. Oxygen free radicals can also increase microvascular
permeability, both by activation of endothelial cell contrac­
tion and by damaging the endothelial cell membrane.
OKY046 has been shown to reverse oxygen free radical-
induced lung injury.130,131 On the other hand, inhibition of
cyclooxygenase did not affect transvascular fluid flux during
phase 2, even though thromboxane A2 is a cyclooxygenase
metabolite.111 This discrepancy is still unexplained; however,
prostacyclin is elevated after endotoxin administration, and
this material has many actions that counter the actions of
thromboxane. Administration of a cyclooxygenase inhibi­
tor will prevent the release of this salutary eicosanoid.
TNF-α is one of the early mediators in systemic inflam­
mation. It has been reported to be elevated during sepsis
and endotoxemia after hemorrhagic shock or thermal
injury. It is considered to be one of the most important
mediators in the cascade because it has the potential to
stimulate or enhance most of the steps in the inflammatory
response. Moreover administration of human recombinant
TNF-α in the chronic sheep model reproduced most of the
effects of endotoxemia, including alterations in pulmonary
microvascular permeability.132,133 TNF-α also induces the
secretion of PAF, which is a further early mediator of sys­
temic inflammation. PAF causes an increase in lung lymph
flow and permeability to protein when it is infused into con­
scious sheep.134 Administration of a PAF antagonist abol­
ished the cardiopulmonary response that occurs during
phase 1 and attenuated it during phase 2. However, PAF
had no direct effect on endothelial cells. This suggests that
it probably increases microvascular permeability through
other mechanisms, such as its priming effect on PMNs.135,136
If burn patients are adequately resuscitated, they most
commonly enter into a phase characterized by hyperdy­
namic cardiovascular function. The hyperdynamic cardio­
vascular response is associated with profound changes in
pulmonary transvascular fluid flux in the ovine model of
continuous endotoxemia.104,137 The lymph protein concen­
tration gradually decreased after phase 2, and after 24
hours of endotoxemia, the reflection coefficient to protein
was at baseline level, whereas the lymph flow was still high.
Microvascular hydrostatic pressure, evaluated by Hollo­
way’s technique, was not significantly different from base­
line.138 The elevated transvascular fluid flux was attributed
to a high filtration coefficient. An increase in both perfused
surface area and pore numbers might have contributed to
the change in filtration. Repeated injections of endotoxin
also reduced subsequent lung lymph production in response
to endotoxin.132 These changes in lung lymph flow were
associated with elevations in endothelin and atrial natri­
uretic peptide.138,139 However, further studies must deter­
mine whether these factors affect pulmonary microvascular
changes during the late phases of sepsis and multiple organ
failure.

19  •  The Systemic Inflammatory Response Syndrome
220
contribute to SIRS after severe burn injury. Widespread
increases in microvascular permeability lead to intravascu­
lar hypovolemia and interstitial edema, thereby impairing
oxygen diffusion to the tissue. Blood flow may become mal­
distributed owing to a loss of vasoregulatory function and
as a result of widespread microthrombosis. Oxygen utiliza­
tion also appears to be impaired. The resultant hypoxic cell
damage further promotes organ dysfunction. Oxygen free
radicals, peroxynitrite, and cytokines also appear to con­
tribute to tissue damage and organ dysfunction. Despite
improved understanding of the cellular and molecular
mechanisms underlying SIRS, targeting the inflammatory
response is not currently an effective treatment option for
patients with burn-induced SIRS. Treatment is supportive
and includes adequate fluid resuscitation, appropriate use
of vasoactive drugs, support of failing organ systems, exci­
sion of necrotic tissue, and treatment of infection with
antibiotics.
Complete references available online at http://

Further Reading
dos Santos CC, Gattas DJ, Tsoporis JN, et al. Sepsis-induced myocardial
depression is associated with transcriptional changes in energy metabo­
lism and contractile related genes: a physiological and gene expression-
based approach. Crit Care Med. 2010;38:894-902.
Goldstein B, Giroir B, Randolph A. International pediatric sepsis consensus
conference: definitions for sepsis and organ dysfunction in pediatrics.
Pediatr Crit Care Med. 2005;6(1):2-8.
Muckart DJ, Bhagwanjee S. American College of Chest Physicians/Society
of Crit Care Med Consensus Conference definitions of the systemic
inflammatory response syndrome and allied disorders in relation to criti­
cally injured patients. Crit Care Med. 1997;25(11):1789-1795.
Szabó C, Módis K. Pathophysiological roles of peroxynitrite in circulatory
shock. Shock. 2010;34(suppl 1):4-14.
Westphal M, Enkhbaatar P, Schmalstieg FC, et al. Neuronal nitric oxide
synthase inhibition attenuates cardiopulmonary dysfunctions after
combined burn and smoke inhalation injury in sheep. Crit Care Med.
2008;36:1196-1204.
administration of endotoxin, thereby accounting for some
of the vasoconstrictive phenomena seen in phases 1 and
2.155 Inducible NOS (iNOS) is the major NOS isoform induced
during acute inflammation. Depending on the species, cells
producing the inducible NOS upon stimulation by endo­
toxin, TNF-α, IL-1, or IFN-α include macrophages, vascular
smooth muscle cells, and vascular endothelium.156 NO is a
lipophilic gas that can easily enter vascular smooth muscle
cells where it stimulates the soluble guanylate cyclase to
synthesize cyclic guanosine monophosphate (cGMP).157,158
High levels of cGMP stimulate cells to lower their intracel­
lular Ca2+ concentration. This leads to vascular dilatation
and hyporesponsiveness to vasoconstrictors. Administra­
tion of an NOS inhibitor to septic humans and to endotox­
emic sheep increases their vascular resistance and restores
their responsiveness to vasoconstrictors.159–161 Overall it
appears that NO is an important mediator of SIRS-induced
vascular alterations. However, administration of NOS
inhibitors in humans has not improved overall outcome
during sepsis or SIRS. Therefore, the mechanisms by which
NO alters vascular function during SIRS in humans require
further investigation.
Peroxynitrite is an additional NO-associated factor that
appears to contribute to SIRS-induced pathology. Peroxyni­
trite is a free radical that is generated through interactions of
NO and oxygen free radicals during periods of severe inflam­
mation and is known to cause cellular injury and organ
dysfunction in experimental burn models.162,163 Treatment
of burned sheep with a peroxynitrite degradation catalyst
has been shown to reduce lung injury in an ovine model of
burn and smoke inhalation injuries.164 Therefore peroxyni­
trite appears to be an important mediator of organ injury
during periods of systemic inflammation. However, further
research is needed to determine the efficacy of treatment
approaches aimed at promoting peroxynitrite degradation
and neutralization in the clinical setting.
Conclusion
Burn injuries, associated ischemia–reperfusion injury, the
presence of necrotic tissue, and sepsis are all events that
Endothelial
stimulation
Endothelium
Cytotoxicity
Activation
stimulus
Calcium influx
and eNOS
activation
eNOS
eNOS
NO
NO
NO2 + OH- ← O2
- + NO
Microbe
Macrophage
Fig. 19.11  Nitric oxide is an important mediator of inflammation-induced vasodilation, myocardial depression, and organ injury. The synthesis of nitric
oxide is mediated by three major nitric oxide synthase (NOS) isoforms.

220.e1
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221
Host Defense Antibacterial
Effector Cells Influenced by
Massive Burns
MAKIKO KOBAYASHI, TRACY TOLIVER-KINSKY, and FUJIO SUZUKI
20 
against enteric bacteria in severely burned mice (Fig.
20.1). In addition, polymicrobial sepsis frequently occurs
in severely burned patients. Because such infections do not
usually develop in healthy individuals, immune dysfunc­
tions associated with burn injuries are a major reason for
the increased susceptibility of severely burned patients to
these infections.
The innate immune system is the first line of host defense
against microbial invasion.21 The cells and molecules of
innate immunity are rapidly activated by microbes or some
signals induced by damaged tissues.22–25 The innate immune
system consists of (1) soluble recognition molecules, (2)
physical barriers, and (3) cellular components (myeloid
cells and lymphoid cells). Soluble recognition molecules
include natural antibodies (IgM and IgA), acute phase pro­
teins, and the complement system. In heathy individuals,
natural IgM is constitutively produced. However, reduced
levels of antibodies are evident in severely burned patients.26
Burn-associated hypermetabolic responses stimulate the
synthesis of acute phase proteins located in the liver and
intestinal mucosa.27–29 Burn injury to tissues leads to com­
plement activation with subsequent depletion of comple­
ment components, mainly C3, C4, and C5.30–32 As physical
barriers, epithelial cells produce antimicrobial peptides
(β-defensins and LL-37/hCAP-18), which are small molec­
ular weight proteins with broad-spectrum antimicrobial
activity.33,34 After injury or infection, epithelial cells produce
alarmins such as thymic stromal lymphopoietin (TSLP),
interleukin (IL)-25 and IL-33. This causes the initiation of
type 2 immune responses.35–37 Although β-defensins are
normally produced by epidermal keratinocytes,33 mRNA
expression of these peptides is greatly decreased in the
tissue around the burn wound when compared with normal
skin in thermally injured patients.38,39 Decreased local pro­
duction of antimicrobial peptides around burn wounds
allows the local growth of bacteria, putting the patient at
risk for wound-derived systemic infections. Studies in
animal models of burn injury suggest that decreased anti­
microbial peptide production by epidermal keratinocytes
around burn wounds is due to the infiltration of suppressive
myeloid and lymphoid cells that appear in response to burn
injuries.
It is well established that burn injury initiates an early
proinflammatory innate immune response followed by an
adaptive counter-inflammatory response.40–42 The innate
immune system is activated in response to either pathogen-
associated or damage-associated molecular patterns.22–25
Both patterns are recognized by pattern recognition
Introduction
Infectious complications are one of the leading causes of
death in patients with severe burn injuries.1–5 Increases in
the total body surface area and depth of burn injuries cor­
relate with the excessive risk of infectious complications.6
Burn patients are commonly treated with many compo­
nents such as fluid resuscitation, wound excision, grafting
and coverage, infection control, and nutritional support.
Progress in each treatment has contributed significantly to
reduce mortality in severely burned patients. However mor­
tality rates associated with infectious complications still
remain high, and bacterial infections are a major cause of
morbidity in burned patients.7–9
Infections in severely burned patients frequently occur as
opportunistic infections. In these patients, a majority of the
causative infectious pathogens come from their own micro­
biota distributed in and on the skin, respiratory tract, and
intestines.5 For example, staphylococci are found in 40% of
wound isolates, and 14%–17% of burned patients become
infected once they are colonized.10–12 Although antibiotics
are useful to control infections, excessive antibiotic usage is
directly related to the development of methicillin-resistant
Staphylococcus aureus (MRSA).13 Vancomycin is utilized
clinically to treat MRSA; however, the management of inva­
sive MRSA infection will become a serious problem if VISA/
GISA strains spread widely.14–16 Currently, newer antibiot­
ics such as linezolid (oxazolidinones) and quinupristin/
dalfopristin (macrolides) are available to treat MRSA infec­
tion.17 In general, however, these agents are of limited
usefulness because of their propensity to create antibiotic-
resistant bacteria.13 These facts strongly indicate that a new
strategy, apart from antibiotic therapy, is required to treat
infections.18,19
Sepsis stemming from wound infections is usually found
in patients with severe thermal injuries. Topical antibacteri­
als (silver sulfadiazine, silver nitrate, mafenide acetate, etc.)
are very useful for controlling the colonization and multipli­
cation of microorganisms on the surface of burn wounds.
However, due to the burn-induced defects of the host’s
antibacterial defenses, very small amounts of Pseudomo­
nas aeruginosa that escape from this treatment are enough
to spread throughout the whole body.20 In fact, only 50
colony-forming units (CFU) of P. aeruginosa applied to burn
wounds are sufficient to kill severely burned mice, whereas
more than 1 × 108 CFU applied intradermally are required
to kill noninjured mice. Similarly, burn-associated defects
in host antibacterial defenses have been demonstrated

20  •  Host Defense Antibacterial Effector Cells Influenced by Massive Burns
222
that neutrophils leave the bloodstream only at the inflam­
matory site.59 This process includes tethering (capturing),
rolling, adhesion, crawling, and transmigration. IL-8 pro­
duction by activated neutrophils plays a central role in the
recruitment of additional neutrophils to the infection site.60
After severe burn injuries, levels of IL-8 in plasma are
approximately 60 times higher than those in plasma of
healthy controls.61 An increase in peripheral blood neutro­
phils is seen in patients 2–5 days after burn injury. However,
the chemotactic function and efficient migration of neutro­
phils are impaired in severely burned patients due to the
decreased expression of CXCR2 (a receptor for IL-8).62
Migration speed of neutrophils toward the chemoattractant
source is also impaired in severely burned patients.63 Such
impairment of neutrophils starts as early as 24 hours after
burn injury, reaches a maximum at 3 to 5 days after burn
injury, and correlates to the size of the burn injury.
IMPAIRED NEUTROPHIL KILLING
Neutrophils are efficient phagocytes that engulf microbes
into phagosomes. The phagosome fuses with granules to
produce a phagolysosome, in which microbes are exposed
to many destructive enzymes, antimicrobial peptides, and
reactive oxygen species.55 These components synergize and
effectively kill microbes. Highly activated neutrophils kill
extracellular microbes by releasing NETs, which consist of
fibrils formed by active expulsion of DNA, chromatin, anti­
microbial protein, and enzymes.64 The sticky DNA fibers of
the NETs bind and immobilize pathogens and thus inhibit
their further spread. NETs kill pathogens directly by means
of antimicrobial histones and proteases. IL-8 is well-known
to enhance NET formations of neutrophils.56,64 As described
earlier, increased levels of IL-8 in the circulation of severely
burned patients have been demonstrated.61 Increased levels
of KC and MIP-2 have also been demonstrated in the sera
and lungs of mice 2–8 hours after burn injury.65,66 KC and
MIP-2 are functionally homologous to human IL-8.
However, phagocytosis, oxidative metabolism, granular
enzyme contents, and intracellular killing of neutrophils
are greatly reduced in severely burned patients compared
with those of neutrophils from healthy individuals.67 The
receptors (PRRs) on innate immune cells. Depending on the
molecular patterns recognized, pro- or antiinflammatory
soluble factors are rapidly released from these cells. Thus
the development of burn-associated immunosuppression is
initiated early after burn injury. Antiinflammatory responses
are helpful for wound healing43–45 and the resolution of liver
and intestinal inflammation21,46,47 in burn patients.
However, dysregulated immunosuppression and persistent
inflammation cause immunoparalysis,48 and patients with
immunoparalysis become extremely susceptible to infec­
tions.49 This chapter will discuss cell populations and their
functions involved in innate immunity as influenced by
severe burn injuries.
Neutrophils
Neutrophils are the most abundant white blood cells in the
innate immune system. They are rapidly recruited to the
injury or infection site, where they phagocytose and kill
invading microorganisms.50 The maturation of neutrophils
is under the control of transcription factors PU.1 and C/
EBP.51 During maturation, the neutrophil goes through
several stages, namely myeloblast, promyelocyte, myelo­
cyte, metamyelocyte, band cell, and, finally, polymorpho­
nuclear (segmented) cell.52 In the absence of infection or
inflammation, mature neutrophils die within 15 hours by
caspase 3-mediated spontaneous apoptosis.53,54 Inflam­
matory signals are capable of prolonging the life span of
neutrophils by several days.53 However, even during inflam­
mation, mature neutrophils die by apoptosis or NETosis
(death during formation of neutrophil extracellular traps
[NETs] for extracellular killing) while performing their anti­
microbial function.55,56 These dead neutrophils are engulfed
by macrophages.57
IMPAIRED NEUTROPHIL RECRUITMENT
Mature neutrophils leave the bone marrow and enter to the
circulation.58 Getting neutrophils to the site of infection is
of prime importance, and an elaborate series of adhesion
events between neutrophils and the endothelium ensures
Mortality (%)
P. faecalis (log10 CFU/mouse)
25
8
9
7
6
5
4
3
Burn mice
Normal mice
100
75
50
B
Mortality (%)
P. aeruginosa (log10 CFU/mouse)
25
1
8
7
6
5
4
3
Burn mice
Normal mice
2
100
75
50
A
Fig. 20.1  Susceptibility of burn mice to Pseudomonas aeruginosa and Enterococcus faecalis infections. Severely burned mice are 104-times or more
susceptible to P. aeruginosa (A) or E. faecalis (B) infection when compared to normal mice.

20  •  Host Defense Antibacterial Effector Cells Influenced by Massive Burns
223
from slightly burned (5% TBSA burn, MRSA-resistant
hosts) or severely burned mice (25% TBSA burn, MRSA-
susceptible hosts) are biologically and histologically differ­
ent from the neutrophils isolated from naïve mice. These
three neutrophil populations have unique cytokine/
chemokine-producing patterns. Also, these three neutro­
phils express Toll-like receptors (TLRs) and surface CD49d/
CD11b integrins differently. Neutrophils isolated from
MRSA-resistant mice are proinflammatory IL-12+ CCL3+
attenuating CXCR2 expression on neutrophils is,62 at least
in part, responsible for neutrophil dysfunction following
burn injury.
PRO- AND ANTIINFLAMMATORY NEUTROPHILS
Experimental studies in rodents have identified distinctive
types of neutrophils that affect resistance to MRSA
infections in burned mice (Fig. 20.2).68 Neutrophils isolated
Counts
CD49d
0
20
40
60
80
100
101
102
103
104
100
Counts
CD11
0
20
40
60
80
100
101
102
103
104
100
Counts
0
20
40
60
80
100
101
102
103
104
100
Counts
0
20
40
60
80
100
101
102
103
104
100
Counts
100
101
102
103
104
Counts
0
40
80
120
160
100
101
102
103
104
200
240
0
40
80
120
160
200
240
C
ALP
MPO
Wright-Giemsa
PMN-N
PMN 1
PMN 2
B
Properties
CCL2
CCL3
IL-12
IL-10
IL-4
TNF-
IL-1
CXCL1
M1M induction
M2M induction
H2O2
Killing
TLR2
TLR4
TLR5
TLR7
TLR8
TLE9
-actin
PMN-N
trace
trace
trace
trace
trace
0.8 ng/ml
3.9 ng/ml
1.7 ng/ml
no
no
<0.2 nmol
0%
PMN 1
trace
11.6 ng/ml
0.5 ng/ml
trace
trace
0.6 ng/ml
3.6 ng/ml
10.7 ng/ml
yes
no
7.8 nmol
58%
PMN 2
17.1 ng/ml
trace
trace
1.3 ng/ml
0.05 ng/ml
0.6 ng/ml
3.5 ng/ml
11.1 ng/ml
no
yes
5.8 nmol
47%
A
Fig. 20.2  Properties of PMN-N, PMN 1, and PMN 2. Peripheral blood neutrophils (PMNs), isolated from slightly burned mice (5% TBSA burn, PMN 1) or
severely burned mice (25% TBSA burn, PMN 2), were biologically and histologically different from naive mouse neutrophils (PMN-N). (Modified from
Tsuda Y, Takahashi H, Kobayashi M, et al. Three different neutrophil subsets exhibited in mice with different susceptibilities to infection by methicillin-resistant
Staphylococcus aureus. Immunity. 2004;21:215–226.)

20  •  Host Defense Antibacterial Effector Cells Influenced by Massive Burns
224
and CCL2 released from PMN 2 are characterized as active
cytokines that induce M2 macrophages from quiescent
macrophages.68,70,71 Therefore these cytokines are targets
for the macrophage polarization influenced by PMN 2.
Infectious complications due to MRSA infection and enteric
bacterial translocation have been successfully controlled in
severely burned mice depleted of CCL2 or IL-10 by their
antisense oligodeoxynucleotide (ODN).72,73 Thus antiin­
flammatory neutrophils appearing in hosts after severe
burn injury suppress effective immune responses and
increase susceptibility to infections.
ROLE OF DAMAGE-ASSOCIATED MOLECULAR
PATTERNS IN INDUCING ANTIINFLAMMATORY
NEUTROPHILS POSTBURN INJURY
In microbial infection, pathogen-associated molecular
patterns (PAMPs) present in diverse organisms but, when
absent in the host, provide exogenous signals that alert
the immune system to the presence of pathogens, thereby
promoting immunity.74 For instance, bacterial lipopolysac­
charide (LPS) is a PAMP and is recognized by TLR4 on the
immune cell surface. Bacterial DNA that contains unmeth­
ylated CpG motifs is also a PAMP and is recognized by TLR9,
which is located in the endosomal compartment of neutro­
phils. Both TLR4 and TLR9 are PRRs. In contrast, a variety
of stressed, injured, or dying cells (including epithelial cells
following burn injury) release damage-associated molec­
ular patterns (DAMPs) as the endogenous danger signals
that alert the innate immune system to unscheduled cell
death and microbial invasion and in response to stress (Fig.
20.3).22–25 HMGB1, hyaluronic acid, formyl peptides, heat-
shock protein 70, S100A8, S100A9, and serum amyloid
A are well-known DAMPs. These DAMPs are specifically
recognized by several receptors (Table 20.1).75 These
ligand-specific interactions are able to induce either pro- or
antiinflammatory effects. In severely burned patients, cir­
culating mitochondrial DAMP levels are notably elevated
(>10-fold) within 72 hours of burn injury. These mito­
chondrial DAMPs cause systemic inflammation, which is
commonly characterized by fever, leukocytosis, increased
cells (PMN 1 or N1), whereas neutrophils from MRSA-
susceptible mice are an antiinflammatory IL-10+ CCL2+
cells (PMN 2 or N2). Neutrophils isolated from naïve mice
are IL-12− and IL-10− cells. These neutrophils also differ in
their promotion of macrophage differentiation. Quiescent
macrophages from the lamina propria of normal mice
convert to the M1 phenotype after cultivation with poly­
morphonuclear leukocyte (PMN) 1 in dual-chamber tran­
swells supplemented with a mixture of TLR3/TLR9 agonists.
In contrast, quiescent macrophages convert to the M2 phe­
notype after cultivation with PMN 2 in the same transwells.
Neither M1 nor M2 macrophages appear even when quies­
cent macrophages are transwell-cultured with naïve PMN.
Also, PMN 2 are shown to be inhibitory for macrophage
conversion to the M1 phenotype under stimulation with
TLR3/TLR9 agonists. Subsequently, IL-10 and CCL2 pro­
duced by PMN 2 are identified as inhibitors of TLR3/TLR9-
induced macrophage polarization toward the M1 phenotype.
Another distinguishing feature is their morphology.
Although IL-12−and IL-10− neutrophils have a round
nucleus, PMN 1 has a multilobular nucleus (indicative of
mature neutrophils), and the nucleus of PMN 2 is ring-
shaped. PMN 2 is predominantly demonstrated in severely
burned mice.68
Furthermore the role of PMN 1 and PMN 2 on host anti-
MRSA resistance has been examined in γ-irradiated NSG
mice (lacking the functional immunocompetent cells)
reconstituted with normal mouse macrophages (Mϕ-
reconstituted γNSG mice).68 Mϕ-reconstituted γNSG mice
become more resistant after inoculation with PMN 1,
whereas the same mice become susceptible after inocula­
tion with PMN 2. Additionally, γNSG mice are shown to be
resistant against MRSA infection when they are inoculated
with normal mouse macrophages previously cultured with
PMN 1. Macrophages previously cultured with PMN 2 do
not protect Mϕ-reconstituted γNSG mice infected with a
lethal dose of MRSA. Similar results are obtained when
Mϕ-reconstituted γNSG mice are orally infected with a
lethal dose of Enterococcus faecalis.69 These results indicate
that MRSA infection and E. faecalis translocation are not
controlled in hosts predominantly bearing PMN 2. IL-10
Table 20.1  Receptors of Pathogen-Associated Molecular Patterns (PAMPs) and Damage-Associated Molecular Patterns
(DAMPs)
Receptor
PAMPs
DAMPs
TLR1/TLR2
Lipopeptide
Serum amyloid A
TLR4
LPS
Fatty acid
Hyaluronic acid
S100A8/A9
NLRP3
Uric acid
Uric acid
ATP
RIG-1, MDA5, TLR7/8
Viral RNA
Immune complex of snRNPs
TLR9
Bacterial DNA
Self-DNA-containing immune complex
Histone
RAGE
HMGB1
DAI, IFI16, AIM2, H2B,
RNA polymerase III
Bacterial DNA, viral DNA
Self-DNA
AIM2, Absent in melanoma 2; ATP, adenosine 5′-triphosphate; DAI, DNA-dependent activator of IFN-regulatory factors; DAMPs, damage-associated molecular
patterns; HMGB1, high mobility group box-1; H2B, histone H2B; IFI16, interferon-inducible protein 16; LPS, lipopolysaccharide; MDA5, melanoma
differentiation-associated protein 5; NLRP3, the NOD-like receptor family, pyrin domain-containing protein 3; PAMPs, pathogen-associated molecular
patterns; RAGE, receptor for advanced glycation end products; RIG-1, retinoic acid-inducible gene 1; TLR, Toll-like receptor.
Modified from Jounai N, Kobiyama K, Takeshita F, et al. Recognition of damage-associated molecular patterns related to nucleic acids during inflammation
and vaccination. Front Cell Infect Microbiol. 2013;2:168.

20  •  Host Defense Antibacterial Effector Cells Influenced by Massive Burns
225
Stressed,
damaged, or
infected tissue
Inflammatory
response
TLR or CLR
MAMPs
DAMPs
Pathogens
Commensal
bacteria
NLR or TLR
C
NLR agonists and
inflammasome
activators
Endogenous
TLR agonists
TLR or CLR
Sterile
inflammation
DAMPs
Alarmins
Injury and
tissue damage
NLR or TLR
B
Tissue
damage
Tissue cell
NLR or TLR
Inflammatory
response
TLR or CLR
PAMPs
DAMPs
Pathogens
A
Fig. 20.3  Pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). (A) PAMPs (including TLR, NLR, and
CLR ligands) mediate the induction of proinflammatory cytokines in response to infection. (B) DAMPs or alarmins released from dead or dying cells
mediate the induction of proinflammatory cytokine production from tissues in response to injury or stress. (C) In combination with DAMPs released
from pathogen-infected or damaged host cells, microorganism-associated molecular patterns (MAMPs) mediate the induction of proinflammatory
cytokines in response to pathogens. ATP, Adenosine 5′-triphosphate; CLR, C-type lectin receptor; NLR, NOD-like receptor; TLR, Toll-like receptor. (Modi­
fied from Mills KH. TLR-dependent T cell activation in autoimmunity. Nat Rev Immunol. 2011;11:807–822.)

20  •  Host Defense Antibacterial Effector Cells Influenced by Massive Burns
226
proliferation under homeostatic conditions and in response
to inflammation.99,100 Peripheral blood monocytes are
classified into three different populations. In humans,
these populations correspond to CD14++CD16− (classical
monocytes), CD14+CD16+ (intermediate monocytes), and
CD14+CD16++ (nonclassical monocytes); and in mice the
equivalent populations are Ly6C+CD62L+CD43−CCR2+
(classical monocytes), Ly6CintCD62L−CD43+CCR2− (inter­
mediate monocytes), and Ly6C−CD62L−CD43+CCR2− (non­
classical monocytes).101 Classical monocytes can transport
antigens to lymph nodes with minimal differentiation
changes from their state in blood, although a proportion
can convert to nonclassical monocytes. However, in the
context of inflammation, recruited monocytes differenti­
ate to macrophages. These monocyte-derived macrophages
are distinct from resident macrophages.102 Severe burn
injuries induce inflammation in various organs including
liver, intestine, and lung due to burn-induced hypermeta­
bolic responses.103 In these tissues, yolk sac-derived tissue
macrophages coexist with monocyte-derived macrophages.
Studies to determine the functional differences of these
macrophage subsets in the organs of severely burned hosts
are needed to develop therapeutic approaches for proper
resolution of inflammation.
M1 MACROPHAGES AS AN ANTIBACTERIAL
EFFECTOR CELL
In steady-state conditions, macrophages are immunologi­
cally quiescent. In the event of infection, quiescent macro­
phages are activated through the engagement of TLRs or
the binding of IFN receptors.104 IFN-γ induces downstream
phosphorylation of Signal transducer and activator of tran­
scription 1 (STAT1). In particular, LPS activates TLR4,
which affects mitogen-activated protein kinases (MAPK),
interferon regulatory factors (IRF), and nuclear factor
kappa B (NF-κB) pathways. Thus, the activation of tran­
scription factors NF-κB, activator protein 1 (AP-1), CCAAT/
enhancer-binding protein α (C/EBPα), Krüppel-like factor 6
(KLF6), IRF5, and STAT1 promote macrophage polariza­
tion toward the M1 phenotype.85,104,105 M1 macrophages
exhibit (1) high oxygen consumption, (2) the ability to kill
cells infected with intracellular pathogens, (3) the ability to
express inducible nitric oxide synthase (iNOS), and (4) the
ability to secrete nitric oxide, some proinflammatory cyto­
kines, Th1 response-associated cytokines, and various
chemokines.87–89 Thus the dissemination of bacteria follow­
ing local infection is prevented by M1 macrophages. M1
macrophages have been demonstrated in bacterial translo­
cation site tissues such as lamina propria (LP) and mesen­
teric lymph nodes (MLNs)106,107 and are the major effector
cells in host antibacterial resistance against enterococcal
translocation.
M2 MACROPHAGES AS INHIBITORS FOR
MACROPHAGE POLARIZATION FROM
QUIESCENCE TO THE M1 PHENOTYPE
Even though M1 macrophages play a role in host anti­
bacterial responses, sustained inflammation can be very
detrimental to the host. For controlling inflammation-
associated damage, a large number of M2 macrophages
secretion of adrenocorticotropic hormone and glucocorti­
coids, and alterations in plasma protein concentrations.76–78
Simultaneously, these DAMPs cause desensitization of
chemokine receptors and formyl-peptide receptors on
neutrophils. Neutrophils influenced by DAMPs lose their
antimicrobial functions. Also, Clec12a (binding to uric acid
crystals) mediates the antiinflammatory response of neu­
trophils influenced by DAMPs.79 Antiinflammatory neutro­
phils secrete high amounts of IL-10 and CCL2,68,69 potent
antiinflammatory cytokines, and have been implicated in
impaired host antibacterial immunity in severely burned
patients.80
SUPPRESSING ADAPTIVE IMMUNITY
Neutrophils have long been recognized as professional killer
cells. They also participate in adaptive immunity. PMN 1
stimulates naïve T cells to polarize to T helper (Th1) cells
through the production of interferon (IFN)-γ and IL-12,
whereas PMN 2 promotes Th2 responses through the pro­
duction of CCL2 and IL-10.68 Because PMN 2 (but not PMN
1) appears in severely burned patients80 and Th2 responses
develop in these patients,81–83 the blockage of PMN 2 is a
potential effective strategy to control Th2 responses in
severely burned patients.
Macrophages
Macrophages play a pivotal role in recognizing and elimi­
nating various microbes. Macrophages, together with den­
dritic cells (DCs), function as antigen-presenting cells.
Together with natural killer (NK) cells and lymphocytes,
macrophages eliminate microbes. Macrophages are charac­
terized by plasticity and flexibility.84–86 Depending on the
environmental stimuli, macrophages have a wide array of
functions, especially in the modulation of innate immune
responses through the release of several factors. Macro­
phages have been primarily classified into two major phe­
notypes: M1 and M2.87–89
TISSUE MACROPHAGES AND INFILTRATING
MONOCYTE-DERIVED MACROPHAGES
In various tissues, macrophages acquire long-term, respec­
tive populations (e.g., peritoneal macrophages in the perito­
neal cavity, Kupffer cells in the liver, alveolar macrophages
in the lungs, microglia in the brain, etc.). Kupffer cells,
microglia, and cardiac tissue macrophages are primarily
yolk sac-derived cells.90 Recent growing evidence clearly
shows that yolk sac-derived tissue macrophages are self-
maintained throughout adulthood.91–93 The development
and maintenance of tissue macrophages require specific
growth factors and are regulated by tissue-selective tran­
scriptional factors.94 For example, macrophage colony-
stimulating factor (M-CSF) is essential for Kupffer cells;95
transforming growth factor (TGF)-β1 and IL-34 are essen­
tial for microglia and Langerhans cells;96,97 and granulo­
cyte macrophage colony-stimulating factor (GM-CSF) is
essential for alveolar macrophages.98 The transcription
factor GATA6 is responsible for the transcriptome profile
of resident peritoneal macrophages as well as for their

20  •  Host Defense Antibacterial Effector Cells Influenced by Massive Burns
227
may be an effective therapeutic target for controlling oppor­
tunistic infections in severely burned patients.
PLASTICITY OF VARIOUS PHENOTYPES OF
MACROPHAGES
Macrophages easily switch from one functional phenotype
to another in response to new microenvironmental
signals.84–86 Shortly after severe burn injury, quiescent mac­
rophages switch to the M1 phenotype in response to invad­
ing pathogens. Subsequently, certain microRNAs (miRNAs)
are produced in M1 macrophages through this stimulation
or after efferocytosis of apoptotic phagocytic cells, which
skews these macrophages toward the M2 phenotype.117–119
miRNAs are short noncoding RNAs of approximately
21–23 nucleotides that function in RNA silencing and post-
transcriptional regulation of gene expression.120 Further­
more M2a macrophages can switch to quiescent
macrophages depending on the presence of IL-4121 or be
reprogramed to switch to M1 macrophages in response to
TLR agonists. Therefore the M2a phenotype is transient and
relatively short. In vitro, M2a macrophages lose their prop­
erties within 2 days of cultivation in IL-4-depleted media
(Fig. 20.4B). In contrast, M2b macrophages live longer
once they appear and do not require exogenous growth
factors (e.g., IL-4), due to the self-sustaining production of
CCL1, which is an essential chemokine for the maintenance
of M2b properties.114 These results indicate that M2b mac­
rophages have poor plasticity and may explain why M2b
macrophages are persistent in severely burned hosts.
Innate Lymphoid Cells
Innate lymphoid cells (ILCs) are a population of lymphocyte-
like lineage-negative (Lin−; i.e., lacking surface markers for
T, B, NK, and monocytes/macrophages lineages) cells.
These cells are present in a wide variety of epithelial com­
partments and have important effector functions in the
innate immune response.122,123 ILCs develop from common
lymphoid progenitors that express IL-7Rα (CD127). Mature
ILCs rapidly respond to alarmins emanating from epithelial
cells or from myeloid cells and are potent innate cellular
are generated.108 M2 macrophages suppress the develop­
ment of protective type 1 immune responses to pathogens84
and thereby facilitate uncontrolled or persistent infections.
IL-4 and IL-13, produced by a wide variety of cells (e.g.,
PMN 2, group 2 innate lymphoid cells, NKT cells, Th2 cells,
etc.),68,109 are typical cytokines to induce M2 macrophages.
CCL2, produced by PMN 2, also stimulates M2 macro­
phage generation.70–72 The macrophage polarization to the
M2 phenotype is mediated via the activation of transcrip­
tion factors, such as STAT3/6, KLF4, IRF4, PPARγ, and C/
EBPβ.85,104 Although the activation of NF-κB, STAT1, and
MAPK signaling pathways is required for the macrophage
polarization to the M1 phenotype, IL-10 inhibits these
transcription factors and promotes STAT3 activation.110,111
Therefore M1 macrophages are not generated from quies­
cent macrophages when M2 macrophages are present.
M2 macrophages are composed of three different sub­
types: M2a (which expresses CD163, CD206, FIZZ1/Retna,
Ym1/Chu3l3, and ARG1 and produces IL-10 and CCL17),
M2b (which expresses CD163 and LIGHT, and produces
IL-10, CCL1, TNF-α, IL-1, and IL-6), and M2c (which
expresses CD163, CD206, ARG1, and FIZZ1, and produces
IL-10, TGF-β, and CXCL13).112 IL-4 and IL-13 are inducers
for M2a macrophages. IL-10 and TGF-β in combination
with cortisol (which increases 10- to 50-fold in the plasma
of severely burned hosts within 24 h of burn injury)113 are
inducers for M2c macrophages. Although M2b macro­
phages are generally known to be induced by immune com­
plexes and TLR or IL-1 receptor agonists,112 the mechanism
involved in the appearance of M2b macrophages after burn
injuries remains unclear. Although all three M2 macro­
phages appear in severely burned hosts, the kinetics of the
appearance of each M2 subtype are different. In LP and
MLNs, M2a and M2c macrophages appear 1–4 days after
burn injury in mice, and M2b macrophages appear 1–4
weeks after burn injury (Fig. 20.4A).71,114 In humans, M2b
monocytes are predominantly distributed in the circulation
of patients 7–10 days after burn injury and persist for 1–2
months. M2a and M2c monocytes are present minimally in
the circulation of patients after burn injury.80 Experimental
studies have shown that elimination of M2b macrophages
from severely burned mice improves resistance against
opportunistic infections.114–116 Thus M2b macrophages
1
ARG1
Light
(Beta)-actin
Light
(Beta)-actin
Light
(Beta)-actin
Media
-actin
ARG1
rIL-4
-actin
Anti-CCL1
mAb
2
3
M2aM
Days after cultivation
4
5
1
2
3
M2bM
Days after cultivation
4
5
B
No. of cells/103M
Days after burn injury
100
7
M2cM
M2bM
M2aM
400
300
200
14
21
30
A
Fig. 20.4  M2a, M2b, and M2c macrophages in severely burned mice. (A) M2b macrophages were detected in the mesenteric lymph nodes (MLNs) of
mice 1–3 weeks after burn injury. M2a macrophages lost their properties within 2 days of cultivation in IL-4-depleted media, whereas M2b macrophages
lived longer once they appeared (B).

20  •  Host Defense Antibacterial Effector Cells Influenced by Massive Burns
228
resemblance to cNK cells because they are CD56+ NKp44+
CD161+ cells and express perforin/granzyme, whereas
CD127+ ILC1s are noncytotoxic cells. Both subsets of ILC1s
lack eomes. CD127+ ILC1s express TNF-α and TNF-related
apoptosis-inducing ligand (TRAIL), which can induce apop­
tosis after binding to TRAIL-R1 (DR4) and/or TRAIL-R2
(DR5) on virus-infected cells.126
Many studies have demonstrated that the numbers and
activities of cNK cells decrease due to severe burn
injuries.128–130 In severely burned patients, the expression of
NKG2D (a natural cytotoxicity receptor) by peripheral blood
cNK cells is significantly reduced.131 NKG2D is constitu­
tively expressed on the surface of circulating and tissue-
resident cNK cells. Activated NKG2D stimulates cytotoxic
effects of cNK cells against infected, transformed, or stressed
cells in vitro and in vivo via interactions with NKG2D
ligands (such as MICB and ULBP1) expressed on the surface
of target cells. However, serum concentration levels of
NKG2D ligands (shed from damaged tissues or from other
tissues responding to stress) increase 3- to 20-fold within
24 hours after severe burn injury and are maintained for
several weeks.131 As an active immune-evasion mechanism,
high concentrations of soluble NKG2D ligands may be
involved in suppressed cNK cell activity in severely burned
patients. Little is known about the influence of severe burn
injuries on the numbers and activities of CD103+ CD127low
ILC1s or CD127+ ILC1s. Because impaired IL-12 production
by various antigen-presenting cells has been demonstrated
sources of multiple proinflammatory and immunoregula­
tory cytokines. ILCs are now classified into three groups,
group 1 ILCs (ILC1s), group 2 ILCs (ILC2s), and group 3
ILCs (ILC3s), based on their abilities to produce cytokines
and to express transcription factors typically associated
with Th1-, Th2-, and Th17-type immune responses, respec­
tively (Fig. 20.5).124 ILC1s and ILC3s have a crucial role in
promoting type 1 immune responses that provide protec­
tion against many microorganisms. By contrast, ILC2s have
a role in promoting type 2 immune responses.125 Cell trans­
fer experiments and in vivo fate-mapping approaches have
estimated the half-life for ILC subsets to be 2–3 weeks.126
IMPAIRED ILC1 GENERATION DUE TO IMPAIRED
IL-12 PRODUCTION AFTER BURN INJURY
ILC1s respond to IL-12.123 These cells are the dominant
innate source of IFN-γ (and TNF-α) after infection and have
a role in recruiting inflammatory cells that control infec­
tion. ILC1s, constitutively expressing T-bet, can be divided
into at least three subsets: conventional NK (cNK) cells,
CD103+ CD127low intraepithelial ILC1s, and CD127+
ILC1s.123 cNK cells are CD56+ NKp44+ CD161+ CD127−
cells, and they require eomes and IL-15 for the development
from NK-cell progenitors.127 cNK cells exhibit cytotoxic
activity by degranulating granzyme and perforin, both of
which induce apoptosis of target cells, such as infected epi­
thelial cells. CD103+ CD127low intraepithelial ILC1s bear
IL-7
IL-7
IL-7
IL-15
IL-12
IL-18
IL-12
IL-18
IL-12
IL-18
IL-7
IL-25
IL-33
TSLP
ID2+ ILC
precursor
IL-23
IL-1
IL-23
IL-1
IL-23
IL-1
IL-22
NCR+
ILC3
NCR–
ILC3
LTi
cells
ILC2
IL-5
IL-13
Group 2 ILCs
Group 1 ILCs
ILC1
NK
cells
IFN
IFN
TFN
IL-17
IL-22
IL-17
IL-22
Group 3 ILCs
Fig. 20.5  Classification of innate lymphoid cells (ILCs) into three groups. ILCs are immune cells that belong to the lymphoid lineage, but do not express
antigen-specific receptors. LTi, Lymphoid tissue inducer; NCR, natural cytotoxic receptor; TSLP, thymic stromal lymphopoietin. (Modified from Spits H,
Artis D, Colonna M, et al. Innate lymphoid cells–a proposal for uniform nomenclature. Nat Rev Immunol. 2013;13:145–149.)

20  •  Host Defense Antibacterial Effector Cells Influenced by Massive Burns
229
development from ILC progenitors. GATA3 is also required
for the maintenance and function of mature ILC2s, and
RAR-related orphan receptor (ROR)-α is an essential tran­
scription factor of ILC2 maturation.123,126 In fact, ILC2s are
not detected in any tissues of RORα KO mice.132 In mice, two
distinct ILC2s are isolated: natural ILC2s (ST2+, nILC2s)
and inflammatory ILC2s (ST2−, iILC2s).133 nILC2s are
present in steady-state conditions and support the mainte­
nance of IgA secretion from B cells in the intestine, whereas
iILC2s are induced in inflammatory circumstances.
Increased numbers of ILC2s have been detected in the
peripheral blood of severely burned patients (Fig. 20.6A),
as well as in the peripheral blood and lamina propria of
severely burned mice (Fig. 20.6B). After depletion of ILC2
by treatment with a specific inhibitor against the RORα-
dependent transcription factor (SR3335, a synthetic ligand
for RORα133) (Fig. 20.6C), sepsis stemming from enteric
bacterial infections was controlled in severely burned mice
(Fig. 20.6D). Thus ILC2s play an important role in the
in severely burned patients and mice,80,81 burn-associated
defects in IL-12 production cause insufficient activities of
CD103+ CD127low ILC1s or CD127+ ILC1s for the produc­
tion of IFN-γ.
TYPE 2 IMMUNE RESPONSES INDUCED BY
ACTIVATED ILC2S
ILC2s respond rapidly to IL-25, IL-33, and TSLP, which are
produced by epithelial cells and macrophages during
inflammation and infection.123 ILC2s have a crucial role in
boosting type 2 immune responses by producing IL-4, IL-5,
IL-9, and IL-13.125 Although the type 2 immune responses
have important host protective functions to maintain
mucosal homeostasis, hyperreactive type 2 immune
responses suppress the development of protective type 1
immune responses to pathogens and thereby facilitate
uncontrolled or persistent infection. ILC2s constitutively
express high levels of GATA3, which is required for their
Log10 CFU/g organ
4
7
6
5
MLNs
Liver
Kidneys
Normal mice
Burn mice treated with saline
Burn mice treated with SR3335
D
Saline
SR3335
Sca-1
CD127
Saline
SR3335
32.2%
ILC2
Q5
2.76
Q8
30.7
Q7
34.3
13.4%
ILC2
Q5
1.92
Q8
58.9
Q7
25.7
ICOS
Lin
Fold decrease ILC2
0
0.2
0.4
0.6
0.8
1.0
1.2
Burn mice
treated with:
C
Sca-1
Sca-1
Normal mice
PBMC Lin–CD127+ cells
Burn mice
Normal mice
Lamina propia Lin–CD127+ cells
Burn mice
7.89%
ILC2
Q1
41.8
Q4
46.1
Q3
4.13
60.2%
ILC2
Q1
4.36
Q4
13.1
Q3
22.3
3.54%
ILC2
Q3
0.31
Q4
48.0
Q1
48.2
14.3%
ILC2
Q3
5.25
Q4
45.9
Q1
34.5
ICOS
ICOS
Fold increase ILC2
0
2
4
6
8
Burn
mice
Normal
mice
Fold increase ILC2
0
2
4
6
Burn
mice
Normal
mice
B
ILC2
0.10%
CD127
Healthy donor
Lin
CRTH2
CD161
ILC2
1.58%
CD127
Burn patient
Lin
CRTH2
CD161
Fold increase ILC2
0
2
4
6
8
10
12
14
Burn
mice
Normal
mice
A
Fig. 20.6  Innate lymphoid cells-2 (ILC2s) appearing in severely burned patients and mice are responsible for the increased susceptibility to gut bacteria-
associated sepsis. ILC2 increased in PBMCs of severely burned patients (A) and PBMCs and lamina propria (LP) of mice 1 day after burn injury (B). ILC2
decreased in LP of burned mice treated with SR3335 (C). The resistance of severely burned mice to gut bacteria-associated sepsis was improved by
treatment with SR3335 (D).

20  •  Host Defense Antibacterial Effector Cells Influenced by Massive Burns
230
are important for controlling and eliminating infections.
Circulating DCs are significantly depleted in burn patients.
As early as 1 day after injury, burn patients have signifi­
cantly lower numbers of both conventional and plasmacy­
toid classes of DCs. In burn patients who do not develop
sepsis, circulating DCs are restored within a week. However,
in burn patients who develop sepsis during the acute post­
burn recovery phase (within 20 days of injury), DCs are not
restored to normal levels and remain significantly lower
than DC levels in burn patients who do not develop sepsis.139
This suggests that a burn-associated deficit in DCs decreases
the ability of burn patients to fight infection. The inability
to replenish DCs after burn injury is associated with a
decrease in differentiation from their myeloid precursor
cells. Monocytes from burned patients show decreased DC
differentiation potential in vitro and are associated with
high monocyte expression of MafB, a transcription factor
that promotes the differentiation of myeloid progenitor cells
into monocytes instead of DCs. In vitro silencing of MafB in
burn patient monocytes restored their differentiation poten­
tial into DCs.140 This is also observed in mouse models of
burn injury, where the differentiation potential of myeloid
precursors favors the production of monocytes and not
DCs. Severely burned mice show a significant decrease in
DC numbers for up to 2 weeks postinjury, and this is associ­
ated with increased expression of MafB, and a decrease in
the expression of GATA-1, a DC differentiation transcrip­
tion factor.141,142
In addition to depletion of DCs, burn injury also impairs
some DC functions that are critical for effective responses to
infection. Locally, skin DCs are not only depleted near the
burn wound, but their expression of human leukocyte
antigen-D related (HLA-DR; a MHC-II antigen presentation
molecule) and TLR4 (important for DC activation) and their
ability to stimulate T lymphocytes, are impaired after burn
injury.143,144 Local impairment of DC functions can increase
susceptibility to wound infections. Rodent models of burn
injury demonstrate similar impairments in DC functions.
DC expression of TLR4 and production of Th1-associated
cytokines such as IL-12 are decreased, while production of
Th2-associated cytokines such as IL-10 is increased after
burn injury. T-cell activation by DCs is impaired by burn
injury.145,146 Additionally, the ability of DCs to produce anti­
microbial β-defensins is decreased following burn injury,
and this is associated with decreased in vitro killing of bac­
teria.147 Collectively, the burn-induced depletion and impair­
ment of DCs can reduce both innate and adaptive immune
responses to infection.
Experimental studies have investigated pharmacological
stimulation of DC production in mice after burn injury as a
mechanism to restore DC numbers and functions after burn
injury. Treatment of burned mice with the DC growth factor
fms-like tyrosine kinase-3 ligand (Flt3L) after severe burn
injury restores and increases DC numbers, increases DC
production of Th1-associated cytokines, and increases DC
stimulation of neutrophil and lymphocyte activation.148,149
This results in improved bacterial clearance, decreased sys­
temic inflammation, and increased survival in response to
burn wound infection. This suggests that DC impairment
plays a critical role in susceptibility to infections after burn
injury and that DC-targeted therapies may help to restore
immune function in severely burned patients.
impaired host antibacterial defenses influenced by severe
burn injuries.
INTESTINAL ILC3S
Similar to ILC1s, ILC3s have a crucial role in promoting
type 1 immune responses.123 ILC3s are predominantly
present in gut-associated lymphoid tissues. These ILC3s
respond to IL-1β, IL-6, and IL-23, which are produced by
DCs or myeloid cells. They are IL-22 (and IL-17) producer
cells and constitutively express RORγt. ILC3s are classified
into three subsets including lymphoid tissue-inducer (LTi)
cells and two RORγt+ subsets distinguished by their expres­
sion or lack of expression of NK cell receptors (NCR+ ILC3s
and NCR− ILC3s).123,126 LTi cells produce lymphotoxin and
TNF-α and stimulate the mesenchymal cell production of
chemokines and adhesion molecules essential for lymphoid
organogenesis. NCR+ ILC3s express NK-specific molecules
(NKp46 in mice and NKp44 in human); however, these cells
lack cytotoxicity and do not produce IFN-γ. In contrast,
NCR− ILC3s are IFN-γ producers. Through the production
of IL-17, NCR−ILC3s stimulate neutrophil migration and
the secretion of antimicrobial peptides by epithelial cells.134
In the intestine, ILC3s have an important role in regulating
tissue repair.123,135 ILC3s rapidly respond to extracellular
bacterial or fungal infections and produce IL-22 for the
maintenance of the epithelial barrier, production of antimi­
crobial peptides, and suppression of the reactivity of com­
mensal bacteria-specific T cells by presenting a peptide
derived from commensal bacteria. ILC3 crosstalk with mac­
rophages and DCs promotes intestinal homeostasis by
enhancing the levels of regulatory T cells.136 In response to
IL-1β, which is produced by macrophages stimulated with
extracellular bacteria, LTi cells and NCR+ILC3s produce
GM-CSF to promote oral tolerance. ILC3s differentiate into
ILC1s on stimulation with IL-2 and IL-12.137
In severely burned patients, bacteria-elicited IL-12 pro­
duction by macrophages and neutrophils is greatly
impaired.80,81 Also, mitogen-stimulated T-cell production of
IL-2 is decreased in these patients.83,138 The deficiency of
IL-2 and IL-12 production results in minimal differentiation
of ILC3s into ILC1s. The decrease of ILC1s in severely
burned patients leads to reduced antibacterial effector cell
generation and subsequent impaired adaptive immune
responses. Since ILC3s resolve intestinal inflammation and
enhance intestinal barrier function through the stimula­
tion of antimicrobial peptide production by epithelial
cells,123 ILC3s play an important role in reducing bacterial
translocation following severe burn injuries.
Dendritic Cells
DCs are phagocytic cells that play an important role in ini­
tiating both innate and adaptive immune responses to infec­
tion. DCs reside in areas of high antigen exposure, such as
the skin, airway, and intestine. As phagocytes, DCs detect
invading microbes and produce cytokines and antimicro­
bial peptides that can attract and activate other innate
immune cells to limit microbial growth and spread. As
antigen-presenting cells, DCs present antigens to T cells to
initiate adaptive immune responses. Both of these DC roles

20  •  Host Defense Antibacterial Effector Cells Influenced by Massive Burns
231
without inducing exaggerated inflammatory activities will
be the best approach for boosting the immune system and
reducing infection-associated mortality of severely burned
patients. Therefore identification of predictive biomarkers is
necessary for the future development of personalized
immunotherapy for severely burned patients.
Complete references available online at

Summary
The immunological perturbations induced by burn injury
are heterogeneous and may differ in each burn patient.
Therefore, targeting a sole cell type or implementing a
single-agent therapy may not be sufficient to significantly
decrease the morbidity and mortality of severely burned
patients. Defining patient-specific immune deficits and then
targeting these defects with a cocktail of immunotherapies

231.e1
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232
Biomarkers in Burn Patient Care
AMINA EL AYADI, DAVID N. HERNDON, and CELESTE C. FINNERTY
21 
outcome.9 Characterization of the post-burn cytokine
response shows an immediate spike in the expression of
mediators such as IL-6 and IL-8, among others, that then
slowly returns to levels detected in nonburned patients over
the next several weeks to months.8–10 The cytokine expres­
sion profile at the time of admission and during the course
of the hospital stay can predict which patients may develop
sepsis or multiple organ failure (MOF).11–13 The expression
of the following pro- and antiinflammatory cytokines has
been linked to patient outcome: tumor necrosis factor-α
(TNF-α), interferon-γ (IFN-γ), IL-1β, IL-I7, IL-4, IL-6, and
IL-8. Increased expression of inflammatory cytokines con­
tributes significantly to the burn-induced hypermetabolic
response and to the increased incidence of infection and
sepsis. While initial studies focused on the correlation of
single cytokines with patient outcomes,14–18 technologies
allowing detection of multiple proteins at a single time
enable the correlation of analyte expression profiles back
to clinical trajectory or other outcome.11,13 The standard
criteria for diagnosing sepsis in the critically ill are not used
in the burn population due to overlap with the pathophysi­
ological response to burn injury. Because the clinical pre­
sentation of sepsis in the burn patient is sufficiently unique,
a burn-specific definition of sepsis was developed.19 Given
the massive inflammatory, acute-phase, and coagulopathic
responses induced by burn injury10,20,21 and the perturba­
tions of these responses that occur with infection, there are
many candidate biomarkers for the identification and/or
prediction of sepsis and infection.
TNF-α
TNF-α is mainly secreted by activated macrophages imme­
diately postburn. The host immune response is activated by
TNF-α, as is the subsequent release of cytokines following
trauma and infection. TNF-α also plays a role in angiogen­
esis and wound healing.22 Several studies have identified
TNF-α as a predictive marker for the development of septic
complications in burn patients.11,23 In fact, TNF-α expres­
sion is increased immediately post-burn, triggering the
inflammatory response, and then decreasing again.8,9,24 A
later elevation in TNF-α expression appears to be indicative
of the onset of infection or sepsis.23,25
IL-8
IL-8 (or CXCL8) is a chemokine that is released early post-
injury mainly by macrophages. IL-8 is an important protein
related to inflammation, where it plays a key role in the
recruitment of neutrophils and other immune cells to the
site of infection.26 In addition to macrophages, IL-8 is also
released by epithelial cells, airway smooth muscle cells, and
endothelial cells. This chemokine has been shown to be
Introduction
Each year, more than 8 million people are burned. Approxi­
mately 1 million sustain severe burn injuries covering more
than 30% of the total body surface area (TBSA). Burns
cause considerable morbidity and mortality; burn injuries
are often complicated by inhalation injury, infections, and
sepsis, all of which can lead to systemic inflammation,
acute respiratory distress syndrome (ARDS), multiple organ
dysfunction (MODS), and death.1 Despite advances in criti­
cal care and resuscitation, infections develop and lead to
sepsis in 40–60% of burn patients.2–6 The ability to prospec­
tively identify or monitor organ function, infections, clinical
trajectory, or patient outcome in severely burned patients
would enable early intervention, reduce morbidity and
mortality, and significantly lower the cost of clinical care.
In recent years, biomarkers ranging from single proteins
(e.g., procalcitonin, interleukin-8 [IL-8]) to the combina­
tion of variables (e.g., proteins, urinary markers, clinical
parameters) have been used to predict or identify the risk of
infection, sepsis, organ failure, or likelihood of survival, in
patients with severe burns. The first 72 hours postinjury
are critical for the prevention of complications, so the ability
to use biomarkers to guide care during this period enhances
our ability to improve patient care. We and others have
identified candidate biomarkers that can be used to identify
infection or sepsis, predict patient survival, reveal injury
severity, or monitor organ function or wound healing. Bio­
markers can take the form of single molecules, gene or
protein families, injury characteristics, or clinical parame­
ters. A good biomarker can be used for either diagnostic or
prognostic purposes, be sensitive, specific, easy to measure,
and reproducible.7 When applicable, the expression of the
biomarker of interest can be modified by pharmacologic
interventions, and this altered expression then monitored
to determine impact on patient outcome.
Burn injury also affects long-term health and quality of
life. With the many body systems that are impacted and
negative sequelae that can result, the ability to predict
patient outcomes or to determine whether therapy is effica­
cious would enable targeted therapies to improve patient
outcomes. Here we review candidate biomarkers in burn
patients for infections and sepsis, survival, inhalation injury,
organ function, and wound healing.
Prediction of Sepsis and Infection
The expression of pro- and antiinflammatory cytokines is
significantly altered following burn injury,8 and the concen­
tration of these cytokines alone or with respect to each
other (the expression profile) can be used to predict patient

21  •  Biomarkers in Burn Patient Care
233
involved in many cellular processes including cell prolifera­
tion, tissue remodeling, and angiogenesis.27
IL-8 has been proposed as a survival biomarker following
burn injury. Expression of IL-8 has been consistently shown
to be greater in burn patients who do not survive than in
those who do.11,13,14,24 Whereas IL-8 expression returns to
baseline within 8–10 days of injury in burn survivors, IL-8
concentrations remained significantly elevated in the non­
survivors until the time of death.24 When assayed over the
course of hospitalization, the temporal increase in IL-8
expression in nonsurvivors occurs approximately 8–10
days post-burn, which may indicate the initiation of infec­
tion or sepsis. A more recent study has shown that in 468
pediatric burn patients, concentrations of IL-8 that met or
exceeded a cutoff limit of 234 pg/mL were associated with
higher incidence of MOF, sepsis, and mortality.28
IL-6
IL-6 is released by T cells and activated macrophages during
the acute-phase response following injury or trauma and
may lead to inflammation or infection. IL-6 has both pro-
and antiinflammatory properties.29 In burns, IL-6 concen­
trations are significantly increased when compared to IL-6
levels in nonburn volunteers.24 Although the initial spike in
IL-6 elevation reflects the early antiinflammatory response,
chronic and excessive increases in serum IL-6 concentra­
tions following burn injury are associated with a higher
incidence of infection, sepsis, and death.11,16,24 Detection of
IL-6 in serum is significantly greater in nonsurviving versus
surviving burn patients at all time points between the time
of admission and time of death or discharge.11,24
C-REACTIVE PROTEIN
C-reactive protein (CRP) is a serum amyloid P component
belonging to the pentraxin family of calcium-dependent
ligand-binding proteins; it serves as a marker of inflamma­
tion. Synthesis of CRP occurs in the liver and is triggered by
the release of IL-6 in response to tissue damage or infectious
stimuli. Elevation of CRP expression occurs several hours
after the onset of the increase in IL-6.30 CRP measurements
are inexpensive and readily available. High concentrations
of CRP occur with inflammation; however this response is
not specific. In burns, elevation of serum CRP is well
documented.31–33 CRP has been proposed as an early predic­
tor of sepsis in burned children.34 In a study of 918 pediat­
ric burn patients, we found that CRP levels correlate
significantly with burn size and mortality, but the changes
in CRP expression did not correlate with the incidence of
major infections or sepsis in severely burned children.35
Additional studies showed that although CRP may corre­
late with burn size or mortality, the relationship to infection
or sepsis is not well-supported.36
PROCALCITONIN
Procalcitonin (PCT) is a peptide precursor of the hormone
calcitonin, synthesized by the parafollicular cells of the
thyroid gland, and involved in calcium homeostasis. The
major function of calcitonin is to decrease calcium absorp­
tion by osteoclastic cells, which increases circulating
calcium levels. The half-life of PCT is 25–30 hours. Serum
PCT concentrations are significantly increased in response
to infectious stimuli, fungal infections, trauma, and surgery.
In burn patients, elevation of PCT concentrations begins
approximately 4 hours postinjury.37 Following burn injury,
significantly higher concentrations of PCT are reported in
septic versus nonseptic patients.1,37–39 Furthermore it has
been suggested that PCT concentrations be incorporated
into the burn-specific definition of sepsis.37 At present, the
utility of the PCT assay is somewhat limited due to the lack
of availability of rapid, cost-effective tests.
LEPTIN
Leptin is a circulating hormone primarily secreted by
adipose tissue and involved in the regulation of feeding and
energy homeostasis through central nervous system affer­
ent pathways.40 Leptin also plays a role in angiogenesis41
and stimulates T cells and monocytes to induce cytokine
release.42 Recent reports suggest a possible role for leptin as
a biomarker in burns; serum leptin levels are significantly
increased following burn injury.25,41 Leptin concentrations
are elevated in septic burn patients compared to nonseptic
patients and in burn survivors compared to nonsurvivors.25
The increased expression of leptin by septic patients may be
related to leptin’s role in regulating the stress response.27
Elevated expression of leptin may play a crucial role in sur­
vival of acute sepsis. The high leptin concentrations in
septic burn survivors may represent a host defense mecha­
nism against bacterial infection.43
COMBINED PANELS
The combination of multiple proteins may offer greater pre­
dictive ability of patient outcomes. The popularity of tech­
nologies allowing detection of a variety of proteins at a
single time, such as a bead-based multiplex approach or
mass spectrometry, has made the measurement of many
proteins in small amounts of sample easy. As a result, it is
now possible to collect the expression data for a panel of
proteins to determine whether there is a correlation with
patient outcome. By using these techniques, relationships
between protein expression and burn injury or patient
outcome can be established. Using these approaches, it has
been shown that the risk of dying of sepsis is elevated in
pediatric burn patients with increased expression of IL-6
and IL-12p70 alongside reduced TNF-α expression.11
Prediction of Patient Survival
with Clinical Characteristics
The ability to accurately predict which patients have a
reduced likelihood of survival will enable the clinician to
develop a more aggressive treatment strategy in order to
maximize the patient’s chance of survival. Classically, age
and percent TBSA burn were used in the initial trial for
early assessment of patient outcome.44 Furthermore, the
additive influence of the presence of an inhalation injury
or pneumonia could be accounted for in order to refine
prediction of death.45 With improvements in clinical
care, such as resuscitation procedures, better control of

21  •  Biomarkers in Burn Patient Care
234
Protein expression within the bronchoalveolar lavage
fluid (BALF) can also be used to give insight into the effects
of inhalation injury in the burned patient. Profiling of cyto­
kine expression within the BALF from burned survivors and
nonsurvivors revealed that expression of many inflamma­
tory markers, including IL-1RA, IL-1β, IL-2, IL-4, IL-8,
IL-10, IFN-γ, MIP-1β, and TNF-α was suppressed in non­
survivors. Additional studies revealed differences in pulmo­
nary immune hyporesponsiveness in the nonsurvivors that
were responsible for decreased cytokine production. Corre­
lation of the expression of these same cytokines in the
serum with the clinical determination of the severity of
inhalation injury demonstrated that IL-1RA, IL-6, IL-8,
granulocyte colony-stimulating factor (GCSF), and mono­
cyte chemotactic protein 1 serve as biomarkers for lung
injury severity.53 Within the BALF, the detection of raised
concentrations of IL-10 alongside suppressed expression of
IL-12p70 are significantly associated with postburn acute
lung injury.54 Furthermore early detection of increased
IL-10, double-stranded DNA, and hyaluronic acid in the
airway is associated with subsequent development of pul­
monary bacterial infections.54
Resuscitation and
Kidney Function
Fluid resuscitation is guided by the type of fluids to be
administered, flow rate, volume, and frequency. The goal of
fluid management is to correct the hypovolemic shock asso­
ciated with the loss of the skin barrier function without
overresuscitating. Formulae such as the Parkland formula
or the Galveston formula are used to determine the burn
patient’s resuscitation goals. While overresuscitation is
often reported,5 no one protocol has been established for use
by all burn centers. The most recent work by Cancio et al.
promotes the use of computerized tools to assist providers
in the resuscitation of burn patients.55
Volume requirements for resuscitation can be estimated
by patient weight and TBSA burned.56 Inhalation injury,
burn thickness, and time since injury are also involved in
these calculations.57 The actual infusion rate is titrated over
time based on urine output.5 While several studies have
suggested using intrathoracic blood volumes to guide resus­
citation rates, higher ratios of serum pro- to antiinflamma­
tory cytokines were found in these patients when compared
to patients with urine output-guided resuscitation.58 In the
same study, granulocyte, lymphocyte, and monocyte CD
markers were also higher in the urine-guided resuscitation
group compared to patients who receive intrathoracic blood
volume-guided resuscitation, suggesting a shift to an anti­
inflammatory status in this group.
Studies to determine reliable biomarkers for intravascu­
lar volume and renal perfusion in critical care have pointed
to neutrophil gelatinase-associated lipocalin (NGAL) and
B-type natriuretic peptide (BNP) as useful markers to deter­
mine resuscitation strategies. Acute kidney injury was iden­
tified by measurement of NGAL 12 hours earlier than when
using creatinine levels; in patients who had been overresus­
citated, BNP levels were significantly higher.59,60 During
resuscitation following burn, measurement of creatinine,
NGAL, and BNP at the point of care facilitate determination
infections and septic episodes, and the development of new
grafting techniques, mortality following a severe burn
injury has significantly decreased. Three risk factors,
however, are associated with increased mortality: age
greater than 60 years, burn covering more than 40% of
TBSA, and presence of inhalation injury.46
We have reported that the inflammatory and the meta­
bolic responses are positively correlated with burn size47
and that patients with massive burns have a higher inci­
dence of sepsis, inhalation injury, mechanical ventilation
requirement, myocardial infarction, and death.48 To evalu­
ate the effects of clinical complications on patient outcome,
952 severely burned pediatric patients were studied. A
cutoff of 62% of TBSA burned was identified: patients
above this threshold had an increased incidence of sepsis,
MOF, and mortality.48
The assessment of protein expression panels has shown
that these can be used to predict patient survival.13,24
Although clinical characteristics are frequently used to
evaluate the severity of the patient’s health, we have found
that the inclusion of proteomic data and assay results from
the clinical laboratory can improve identification of patients
who may have difficult clinical courses.49 In this study of
322 severely burned children, a panel of biomarkers was
identified, including burn size, presence of inhalation
injury, age, blood urea nitrogen, α-2-macroglobulin, IL-4,
and aspartate aminotransferase. Testing of this model
showed that although prediction of death was only accu­
rate 52% of the time when using burn size, age, and pres­
ence of inhalation injury, by including clinical chemistry
and proteomic data, accuracy could be boosted to 81%.
Inhalation Injury and
Mechanical Ventilation
The severity of burn injury is sometimes complicated by
inhalation injury, which contributes to mortality. Patients
with inhalation injury have an odds of dying nearly three
times higher than those without inhalation injury.48 Mor­
bidity in patients with inhalation injury is further compli­
cated by exposure to inhaled toxins and soot, exposure to
which can predispose the patient to development of respira­
tory tract infections and/or ARDS. Mechanical ventilation
is used to alleviate these symptoms. Biomarker studies have
been performed in burn patients under various ventilation
strategies, such as low tidal volume versus high tidal
volumes. Shelhamer et al. reported that, in mechanically
ventilated patients, an early increase in plasma IL-8 con­
centrations, among other cytokines (IL-1β, IL-6, IL-8,
GM-CSF, and TNF-α), was associated with a several-fold
increase in ventilator-associated pneumonia or death.50
However a recent study compared serum concentrations of
inflammatory cytokines, IL-6, IL-8, and TNF-α before and
after using percussive ventilation in patients with minor
burns and smoke inhalation to determine whether the
plasma levels of these biomarkers are affected by the venti­
lation strategy.51 Unexpectedly this study showed that high-
frequency percussive ventilation (HFPV) increased blood
oxygenation and did not further increase the serum levels
of inflammatory cytokines,51 as was hypothesized by the
Shelhamer et al. study.50

21  •  Biomarkers in Burn Patient Care
235
In elderly patients, delayed wound healing was associated
with increased levels of CD44 and keratin-6.65 Modulation
of matrix metalloproteinase-9 in these patients accelerates
wound healing.65 IL-33, a member of the IL-lβ cytokine
family, was shown to accelerate wound healing, increase
extracellular matrix (ECM) production, facilitate the devel­
opment of activated macrophages, and inhibit meticillin-
resistant Staphylococcus aureus (MRSA) colonization by
activating neutrophil proliferation while increasing expres­
sion of ECM-associated genes.66 Leptin also improved wound
healing by stimulating angiogenesis40 and neovasculariza­
tion in ischemic wounds as part of the autocrine/paracrine
regulation of wound healing.67 TNF-α is an important
factor in wound healing due to its role in the early immune
response when secreted by activated macrophages. TNF-α
may also influence wound healing through direct action on
keratinocytes and endothelial cells, thereby impacting epi­
thelialization and vascularization.68 Therefore TNF-α may
be a good therapeutic target to improve wound healing in
burns.
Conclusion
The utilization of proteomic, genomic, and clinical mea­
surements to predict patient outcomes, monitor injury
severity or organ recovery, or monitor wound healing fol­
lowing severe burn injury is the topic of much research.
With current efforts to precisely define the patient popula­
tion or injury severity (including defining sepsis), future
efforts to identify biomarkers for patient outcomes should
yield markers with greater specificity and utility. By pursu­
ing these efforts, identification and validation of biological
markers that can be used to guide clinical decisions or to
monitor efficacy of therapy will be possible.
Complete references available online at

Further Reading
Davis CS, Albright JM, Carter SR, et al. Early pulmonary immune hypore­
sponsiveness is associated with mortality after burn and smoke inhala­
tion injury. J Burn Care Res. 2012;33(1):26-35.
Finnerty CC, Jeschke MG, Qian WJ, et al. Determination of burn patient
outcome by large-scale quantitative discovery proteomics. Crit Care Med.
2013;41(6):1421-1434.
Finnerty CC, Ju H, Spratt H, et al. Proteomics improves the prediction of
burns mortality: results from regression spline modeling. Clin Translat
Sci. 2012;5(3):243-249.
Jeschke MG, Gauglitz GG, Kulp GA, et al. Long-term persistence of the
pathophysiologic response to severe burn injury. PLoS ONE. 2011;6(7):
e21245.
Kraft R, Herndon DN, Al-Mousawi AM, et al. Burn size and survival prob­
ability in paediatric patients in modern burn care: a prospective obser­
vational cohort study. Lancet. 2012;379(9820):1013-1021.
Ruiz-Castilla M, Roca O, Masclans JR, Barret JP. Recent advances in bio­
markers in severe burns. Shock. 2016;45(2):117-125.
of vascular volume and assessment of renal function.59,61
Additional studies are needed to optimize the cutoffs for
BNP and NGAL that will be used to guide resuscitation.
Wound Healing
Wound closure is predicted based on injury location, wound
perfusion, and the gross appearance of the wound bed and
granulation tissue.62 In the absence of credible algorithms
or biomarkers, quantitation of these factors is subjective.
Therefore determination of biomarkers that can be used to
monitor wound healing or be modulated to achieve optimal
wound healing while avoiding hypertrophic scarring is of
utmost importance in this field. Wound healing is accom­
plished via a precisely orchestrated cascade of interrelated
cellular and biochemical events that lead to repaired tissue
and is accomplished via the following events: inflammation,
migration, proliferation, and remodeling. These phases are
tightly regulated, and each phase overlaps with the previous
one and is characterized by specific markers. The initial
inflammatory phase of wound healing prevents wound
infection through the early immune response and is charac­
terized by vasodilation, fluid extravasation, edema forma­
tion ensured by neutrophils, monocytes, and macrophages,
respectively. The second phase is the proliferative phase,
characterized by activation of fibroblasts and keratinocytes,
which leads to wound closure and revascularization. Finally
the remodeling phase is characterized by collagen and
elastin deposition and differentiation of fibroblasts into
myofibroblasts to help with wound contracture and ulti­
mately wound closure. Finally apoptosis of keratinocytes,
myofibroblast, and immune cells will take place to terminate
wound healing and avoid overgrowing extracellular compo­
nents that may lead to unwanted hypertrophic scarring.
Acute wounds heal by an interdependent sequence of
events mediated by pro- or antiinflammatory cytokines and
chemokines. Determining the levels of these cytokines may
reflect the status of the healing wound. Biomarker studies
aim to determine specific markers that drive each phase of
wound healing in order to tailor therapeutic strategies that
will optimize functional recovery. Possible biomarkers have
been identified by analyzing cytokine levels in the serum,
wound exudate, blister fluid, and wound tissues. From these
studies, increased serum levels of IL-3, IL-12p70, and PCT
have emerged as biomarker candidates indicating delayed
wound healing.63 Hawksworth et al. analyzed the levels of
proinflammatory cytokines in the serum, wound effluent,
and biopsies of the wound bed collected during each
débridement procedure.64 Serum IL-6, IL-8, MIP-l α, and
effluent inducible protein [IP]-10 protein were predictive of
wound dehiscence.64 Additionally, expression of mRNA
transcripts for MCP-l, IL-lα, TNF-α, IL-8, MIP-lα, GM-CSF,
IL-lβ, and IL-6 were also predictive of wound dehiscence.64