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302
M. Hunter and D. T. Harrington
Cardiovascular System
Severe burns create a mixed picture of shock in the first
days after the injury. Due to release of inflammatory mediators, cardiac contractility is decreased, and cardiac output
will be impaired. In addition, patients are simultaneously
losing free fluid from wounds through evaporation as well
as losing intravascular volume through capillary leak into
tissue causing edema. In short, severely burned patients can
have a mix of distributive, hypovolemic, and cardiogenic
shock in the first 24–48h after their injury [3]. In this setting, burn resuscitation is a lifesaving intervention for the
severely burned patient.
Burn Resuscitation
The most important components of burn resuscitation are
quick initiation of crystalloid resuscitation and a closed
loop protocol that allows intensive care providers to titrate
the resuscitation to each patient. A formula like the modified Brooke Formula (2mL/kg/%TBSA burned) estimates
the amount of fluid required in the first 24h with half to
be given in the first 8h. Providers can use this formula to
calculate an initial fluid rate, but the hourly titration of the
intravenous rate is based on the patient’s response including urine output. Recommended urine output is 0.5 mL/
kg/h in adults and 1.0 mL/kg/h in children. Many centers
have adopted a closed loop, computer supported protocol
to assist providers with resuscitation [4]. The importance of
having a protocol, written or computer-assisted, that can
adjust to the fluid demands of each patient cannot be overstated. Burn patients with inhalation injury, significant
electrical injury, or intoxication with alcohol or drugs will
require more resuscitation [5].
14 ICU Care ofBurn Patients
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Invasive Monitoring
In order to facilitate burn resuscitation, patients should
have a Foley catheter placed to monitor urine output and an
arterial line to monitor mean arterial pressure (MAP).
Arterial lines are often needed as blood pressure cuffs can
be inaccurate due to tissue edema. In addition, tissue edema
can cause issues with placement and maintenance of peripheral intravenous catheters, and some severely burned
patients will require placement of a central venous catheter.
These should be placed through unburned skin if possible to
reduce risk of infection, but can go through burned skin if
necessary [2]. Catheters placed through burned skin need to
be changed more frequently than catheters placed through
unburned skin.
In the first 24–48h, most severely burned patients will not
have normal hemodynamics. Due to the decreased cardiac
output, a MAP between 50 and 60mmHg can be tolerated if
urine output and mental status are adequate. Due to the systemic inflammatory response to injury, severely burned
patients will have a baseline tachycardia. Goal heart rate
should be less than about 130 beats/minute [4].
Fluid Creep
While it is important to quickly escalate fluid resuscitation to
combat shock in severely burned patients, it is equally
important to consider de-escalation of fluid infusions to
avoid complications from over-resuscitation as the patient’s
burn shock physiologic changes abate over the 18–24h postburn period. Due to the high fluid requirements needed,
patients with large TBSA burns are at risk of compartment
syndrome, pulmonary edema, and even cerebral edema in
the setting of burn resuscitation. This phenomenon of excess
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M. Hunter and D. T. Harrington
fluid resuscitation that was seen in many burn centers from
1990 to 2010 was called “Fluid Creep” [5]. In order to prevent this, many burn centers utilize “colloid rescue” in the
first 24h to reduce volume of fluid. In addition to colloid use,
protocols for burn resuscitation should have a feedback system that has providers turning down fluid rates as patients
reach goal parameters [4]. Other factors that have been associated with fluid creep are the potential overuse of mechanical ventilation in the first 48 h after burn and overzealous
use of narcotics. Both interventions should be thoughtfully
used in the acute burn setting.
Pulmonary
The effect of severe burns on the pulmonary system can be
from direct effect due to inhalation injury, from systemic
injury from the systemic inflammatory response to injury or
impairment of oxidative metabolism from cyanide and carbon monoxide poisoning. Here, we will cover some topics
specific to burn patients in the intensive care unit.
Airway Injury
Inhalation injury can cause significant concern for upper
airway edema. Thermal injury will be absorbed in the upper
airway, except in the case of steam which can reach further
down the respiratory tract. Traditionally, patients with evidence of facial burns or soot around mouth and nares were
considered at risk for inhalation injury. However, these signs
have been shown to have a poor correlation with need for
intubation. While the best assessment of upper airway
injury is a nasolaryngoscopy for direct visualization [6],
often providers must rely on patient history and clinical
exam to determine the likelihood of upper airway injury
and need for intubation.
14 ICU Care ofBurn Patients
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Airspace Injury
Oxygenation can be compromised in severe burns due to
direct injury from inhaled soot, mists, and fumes or indirect
injury from systemic factors. Inhalation of chemicals or irritants in smoke can damage lungs leading to hypoxia and need
for intubation. Inhalation injury is associated with an
increased need for resuscitation as well as an increased risk of
mortality. Diagnosis relies on clinical judgment and should be
supported by evidence of inhalation injury on bronchoscopy.
Treatment for lower airway inhalation injury is supportive.
Patients will have significant sloughing of mucosa and formation of fibrin casts requiring aggressive pulmonary toilet. For
those requiring intubation, lung protective ventilation is recommended, and bronchodilators may have some benefit [7].
In addition to direct injury, severely burned patients are at
risk for acute respiratory distress syndrome (ARDS) from the
significant systemic inflammatory response to their injury. This
can occur in up to 30% of burn patients requiring intensive care
[2]. This presents as increasing hypoxia occurring days after the
injury with bilateral opacities on chest radiograph as defined by
the Berlin Criteria. Treatment is supportive with lung protective
mechanical ventilation aiming for target tidal volumes of 6mL/
kg of predicted body weight and plateau pressures of
<30 cmH2O. For patients with severe ARDS, other strategies
such as paralysis and proning can improve oxygenation. If all
else fails, providers can consider extracorporeal membrane
oxygenation (ECMO) [8]. Therapy for ARDS is also to look for
and treat any potential underlying drivers of this inflammatory
insult. Identifying and treating sepsis and expeditious removal
of any residual eschar should also be performed [5].
Ventilation
Ventilation is an important consideration in the severely burned
patient. Patients will be compensating for a metabolic acidosis
from tissue hypoperfusion in the setting of shock. Patients with
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M. Hunter and D. T. Harrington
large burns or circumferential burns to the torso may require
escharotomies to allow for improved ventilation [2].
Toxins
Fire environments produce cyanide and carbon monoxide.
Both these toxins poison the ability of the cell to use oxygen
in oxidative metabolism. Direct measurement of the percentage of hemoglobin bound with carbon monoxide is readily
available by blood gas measurement or co-oximeter but measurement of cyanide levels often takes 24–36h in many centers. Development of a metabolic acidosis or unexpected
decrease in mental status should prompt a workup and treatment for these potentially life-threatening toxins.
Infection andSepsis
Skin is an important part of our defense against infection.
Severe burn injury not only causes direct destruction of a barrier to infection but also a global depression of the immune
system leading to an increased risk of infection [9]. Infections
account for 51% of deaths in burn patients with pneumonia,
cellulitis, urinary tract infection, and burn wound infection as
the top sources [10]. However, in the setting of a systemic
inflammatory response to injury, diagnosis can be difficult in
the severely burned patient. For each type of infection, it is
important to consider early source control and early empiric
antibiotics with narrowing according to culture data as soon
as possible. Below are some considerations for common
infections in severely burned patients.
Prevention
The most important part of infection control in critically ill
burn patients is prevention. First, treatment of burn wounds
with early excision and skin grafting reduces the systemic
14 ICU Care ofBurn Patients
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inflammatory effects as well as restoring a barrier against
infection. While wounds are open, topical antimicrobials can
combat bacterial growth [10].
Burn patients with greater than 20% TBSA burns should
have a private room with an elevated ambient temperature to
prevent hypothermia. In addition to strict hand hygiene, providers and visitors should wear gowns, gloves, hats, and masks
to reduce the risk of contamination. These measures have
been shown to reduce the risk of nosocomial infection in the
burn patient [11]. These precautions should be maintained
until less than 20% TBSA burns are open.
To prevent catheter associated infections, it is important to
assess the need for these catheters daily and remove central
lines and Foley catheters as soon as they are no longer
needed. Central lines through intact skin can be changed as
per routine institutional protocols, but catheters through
burn skin may need to be replaced every 3–5days [12].
Sepsis
Detecting sepsis in the severely burned patient requires providers to pay close attention to the patient’s overall condition
to see changes in hemodynamics, metabolism, and laboratory
values. Providers cannot rely on absolute values alone to differentiate sepsis from the background of a systemic inflammatory response to injury which most all burn patients manifest.
In 2007, the American Burn Association Consensus Conference
found that the definition of sepsis used for non- burned patients
did not describe sepsis in burn patients adequately. This consensus conference defined sepsis as “a change in the burn
patient that triggers the concern for infection” [13]. Sepsis
requires three or more of the following criteria:
• Temperature >39°C or <36.5°C
• Progressive tachycardia >110 beats/minute
• Progressive tachypnea >25 breaths per minute or minute
ventilation >12L/min
• Thrombocytopenia <100,000/mcL
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M. Hunter and D. T. Harrington
• Hyperglycemia in the absence of pre-existing diabetes
mellitus
• Inability to continue enteral feeding >24h
AND
• Culture positive infection OR pathologic tissue source
identification OR clinical response to antimicrobials
Pneumonia
The diagnosis of pneumonia can be obscured with a presence
of ARDS and/or inhalation injury. Scoring systems such as
the Clinical Pulmonary Infection Score (CPIS) can guide
providers on screening ventilated patients for ventilatorassociated pneumonia (VAP) [14]. For ventilated patients
where pneumonia is suspected, providers can obtain culture
data with bronchoalveolar-lavage (BAL) to help confirm the
diagnosis and narrow antibiotic coverage.
Burn Wound Infections
Diagnosing a burn wound infection takes careful clinical
judgment. Wounds will become colonized with bacteria
within 24h of burn injury; therefore, the presence of bacteria
does not equate with an infection. In order to diagnose a
wound infection, a quantitative wound culture should be
taken and show >105 bacteria/gram of tissue in the setting of
infection or sepsis. Clinical suspicion can also be used.
Cellulitis, early tinctorial change of the burn eschar, and
premature separation of the burn eschar should raise a clinical suspicion for burn wound infection or sepsis. Treatment
includes intravenous antibiotics and urgent debridement of
infected tissue [13]. In some cases, due to use of broad spectrum antibiotics and the immunocompromised state of major
burns, patients can develop invasive fungal infections. Yeast
infections can be treated with topical and systemic antifun-
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gals as well as debridement. However, fungal infections carry
a high mortality and need to be treated with radical debridement and possible amputation for source control [10].
Metabolism
The body’s metabolic response to a large burn is activated by
pro-inflammatory cytokines and creates a profound hypermetabolic and catabolic state which approaches double the
basal rate [9]. As a result, patients have an increased caloric
need that can approach as high as 110–150% of non-burned
patients [6]. This leads to breakdown of proteins and weight
loss. Significant weight loss can lead to immune dysfunction
and delayed wound healing [15].
Nutrition
The importance of adequate nutrition in burn patients cannot
be overstated. The best measurement of a burn patient’s
caloric need is through indirect calorimetry. However, if this
is not available, caloric needs can be estimated using equations such as the Harris Benedict equation to estimate basal
energy expenditure and adjust for demands of burn injury by
using a multiplier of 1.5 [15]. Enteral feeding should be initiated as early as is feasible and routinely within the first 24h.
In large burn injury, diets and tube feedings should be high in
protein and carbohydrates and low in fat [16]. Burn patients
are at risk for swallowing dysfunction. Inhalation injury, longterm intubation, placement of a tracheostomy tube, long- term
use of nasogastric tubes, and extensive burns to the neck are
risk factors for swallowing dysfunction. Patients with any of
these risk factors should have a comprehensive bedside swallowing evaluation. Aspiration detected on bedside evaluation
should lead to a nothing by mouth status. If no aspiration is
detected on bedside evaluation, then the patient should have
a definitive test to rule-out aspiration such as a modified
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barium swallow (MBS) or fiberoptic endoscopic evaluation
of swallowing (FEES). These definitive evaluations of swallowing are necessary because bedside evaluation alone has a
false negative rate and subsequent silent aspiration of up to
25–30%.
Hyperglycemia
Due to the profound stress response in large burn injuries,
many patients develop insulin resistance resulting in hyperglycemia. This can lead to poor wound healing and loss of
skin grafts. This insulin resistance can persist for months after
a large burn injury. Blood glucose should be followed closely
in all patients with large burns, even those without a history
of diabetes. Subcutaneous insulin can be used to control
blood glucose, and in severe cases continuous intravenous
insulin can be used in the acute setting [16].
Renal
Patients with severe burn injuries are at risk for acute kidney
injury at different phases of their course. About 30% of
severely burned patients will develop acute kidney injury, and
this is associated with an increased mortality [6]. Early kidney
injury is related to burn shock or in some cases compartment
syndrome or direct injury to muscles leading to rhabdomyolysis. In both cases, a robust burn resuscitation is the best
response to early kidney injury. Acute kidney injury that
develops after the initial resuscitation is most often related to
sepsis. Source control and treatment of infection are necessary to prevent ongoing injury.
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Renal Replacement Therapy
Rarely, burn patients will progress to renal failure and require
renal replacement therapy. However, progression to renal
failure is a poor prognostic indicator and is associated with up
to 80% mortality in the burn population. Intermittent hemodialysis can be used for patients with adequate blood pressure. However, more often burn patients in the ICU require
continuous renal replacement therapy (CRRT) due to hemodynamic instability [17].
Palliative Care
Palliative care is an important concept in the treatment of
severely burned patients. Burn patients have significant pain
and stress both from the injury and from the treatment in the
intensive care unit. It is important to have good communication with patients and their families about the prognosis and
course of their treatment as well as understand the goals of
each patient [17]. The use of palliative care teams have been
used in some burn centers with positive effects.
Prognosis
While there are several models for determining mortality in
burn patients, three factors are crucial in determining prognosis: patient age, TBSA burned, and the presence of inhalation
injury [18]. One of the most widely used is the Revised Baux
Score [Age + Percent Burn + 17 × (Inhalation Injury, with
1=yes, 0=no)] which takes into account these factors [19].
In addition to mortality, burn providers should discuss the
expectations of rehabilitation.
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