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146
A. Rodriguez and A. McQuitty
Pathophysiology
Airway injury and respiratory complications may occur in
patients with large TBSA burns, scald burns without head/
neck involvement, prolonged intubation, and direct thermal
inhalation of steam, chemicals, or hot gases [6]. Despite
research gains in nutrition, the hypermetabolic response to
burn injury, and novel skin grafting techniques, there is still
much to be learned about the pathophysiology, inflammatory
response, and long-term consequences of inhalation injury [7].
Inhalation injury may be divided into 3 classes: thermal
injury (restricted to upper airway structures except in cases of
blast injury or steam inhalation), local chemical irritation
throughout the respiratory tract, and systemic toxicity (inhalation of toxins such as carbon monoxide or hydrogen cyanide).
Airway compromise may occur within minutes to days from
severe edema, bronchospasm, and mucous plugs or cast formation. The effects of fire and smoke exposure are pathologic at
several distinct anatomic levels, from mild upper airway inflammation to severe systemic consequences (see Fig.5.1 [8]).
F . Respiratory and systemic effects of inhalation injury.
Source: [8]
Chapter 5. Inhalation Injury
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In the presence of steam, thermal injury to distal lung
tissue occurs as steam has a higher heat capacity than air and
will cause direct injury to the distal tracheobronchial tree [9].
Inhalation of hot dry air does not seem to have significant
effects on the lower respiratory tract, as most of the heat is
dissipated in the nasopharynx (but laryngospasm, supraglottic edema, and possible suffocation may occur). Profound
distal lung injury and death may ensue in smoke inhalation
patients who are entrapped in enclosed spaces with loss of
consciousness. In conscious patients, subglottic injury rarely
occurs, due to the reflex closure of the vocal cords. After
exposure to smoke for an extended period, the following may
occur in varying degrees: initial interstitial edema with
decreased pulmonary compliance/bronchospasm, hypoxemia
(with or without carbon monoxide), loss of hypoxic pulmonary vasoconstriction and resultant ventilation/perfusion
mismatch, and late pneumonia or respiratory failure [9, 10].
Assessment andGrading
The initial assessment of the patient with suspected inhalation
injury should include recognition and immediate treatment
of limb or life-threatening injuries, as burn patients may also
have associated trauma. Large cutaneous burns may distract
physicians from other critical injuries; thus, providers should
follow the guidelines outlined by the American College of
Surgeons and the American Burn Association. Immediate
priorities are outlined by the Advanced Trauma Life Support
(ATLS) and Advanced Burn Life Support (ABLS) courses
[11–13]. The initial focus is airway maintenance (recognition
of current or impending obstruction), cervical spine
protection, adequate ventilation, and maintenance of
perfusion pressure. The presence of hypoxia or respiratory
distress on arrival should alert the provider to rule out other
immediate life-threatening pathology, such as tension
pneumothorax. Oxygen should be initiated in patients with
suspected inhalation injury, and continuous monitoring
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A. Rodriguez and A. McQuitty
should occur, as airway edema will continue to increase over
several hours, especially after fluid resuscitation [14, 15].
Although facial burns may be indicative of a possible
inhalation injury, a history of a closed space flame burn
should be a warning sign [16]. Predictors of inhalation injury
with high sensitivity include a combination of several factors:
large TBSA burn, flame burns in enclosed space, soot in
mouth, and dyspnea [1, 17]. Facial burns, singed hair, and mild
hoarseness are classic signs of probable inhalation injury but
lack sensitivity and specificity [18]. Only completely asymptomatic patients without signs of inhalation injury (see
Denver criteria below) may be discharged from the emergency department setting; otherwise, the patient should be
stabilized and transferred to a burn center or admitted for
close monitoring [19].
Multiple modalities may assist with the diagnosis of
inhalation injury. The current standard for diagnosis of
inhalation injury is bronchoscopy; initial chest radiographs
or computed tomography (CT) scans often appear normal
until secondary complications develop [15]. Inflammation is
progressive, and patients should be assessed by bronchoscopy
on arrival and repeated again within 48h as needed. Chest
radiographs or CT scans may be utilized to identify initial
coexisting traumatic injuries. CT scans with a radiology
score (RADS) to grade severity of inhalation injury may
complement bronchoscopic findings within 24h of injury and
have the advantage of being noninvasive and allowing for
evaluation of the lower airways [19]. Other clinical testing
includes radionuclide studies with xenon-133, pulmonary
function tests, carboxyhemoglobin levels (see Management
section), and arterial blood gas analysis.
All symptomatic patients should have an evaluation by
flexible bronchoscopy and/or nasopharyngoscopy [4, 20] to
estimate the extent of injury and to evaluate the development
of mucosal edema. If these scopes are not available, then
guidelines for evaluation and intubation in a pre-burn center
should be followed (see Management section). A complete
diagnostic exam should be performed by experienced per-
Chapter 5. Inhalation Injury
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149
sonnel, and care should be taken to avoid impairment of airway patency [21]. Nasopharyngoscopy is well-tolerated in
non-intubated patients and should also be performed in
intubated patients to assess pharyngeal edema. Sedation
adjuncts and medications, if needed, include local anesthetic
atomizers (lidocaine), dexmedetomidine, and ketamine. An
antisialagogue/anticholinergic agent, such as glycopyrrolate,
is often added to pediatric regimens. Narcotics and benzodiazepines should be used with caution as they may cause respiratory depression in a difficult airway patient. Children are at
greater risk of airway obstruction (with relatively smaller
airway diameters), as are patients with circumferential burns
to the neck [1, 15]; these patients should be monitored in an
acute care setting with a low threshold for intubation.
A key component of most studies is the importance of
examining symptomatic patients, as many patients with inhalation injuries may not demonstrate the usual signs of facial
burns [20]. Facial burns have a high correlation with true
vocal cord edema, and body burns have a high correlation
with both true and false vocal cord edema (we find this to be
true in large scald burns at our institution). Diagnosis of inhalation injury by evaluation of the upper airway only (with
laryngoscopy or nasopharyngoscopy) is not associated with
poor outcomes or mortality [22]; however, the addition of
bronchoscopic evidence of injury correlates well with mortality and ventilator/ICU days. It is necessary to confirm lower
airway damage by bronchoscopy because physical findings,
such as singed facial hair and carbonaceous sputum in the
oropharynx, are indicators of thermal injury at the level of
the pharynx and cannot predict lower airway damage [23].
The Abbreviated Injury Score (AIS, a bronchoscopic grading
scale), shown in Table 5.1, correlates with subsequent clinical
outcomes and may guide management [3, 24]. A complete
diagnostic exam involves assessment of the supraglottic, glottis
opening, and subglottic (tracheobronchial) areas [25]. Because
airway edema may not occur immediately but may develop
over a period of hours, a high index of suspicion and frequent
reevaluations of the respiratory status are essential [15]. Patients
A. Rodriguez and A. McQuitty
150
T . Bronchoscopic criteria to grade inhalation injury
(Abbreviated Injury Score)
Grade Class Description
0 No injury Absence of carbonaceous deposits,
erythema, edema, bronchorrhea, or
obstruction
1 Mild injury Minor or patchy areas of erythema,
carbonaceous deposits in proximal or
distal bronchi
2 Moderate
injury
3 Severe
injury
4 Massive
injury
Sources for this table [24, 29]
Moderate degree of erythema,
carbonaceous deposits, bronchorrhea, with
or without compromise of the bronchi
Severe inflammation with friability,
copious carbonaceous deposits,
bronchorrhea, bronchial obstruction
Evidence of mucosal sloughing, necrosis,
endoluminal obliteration
with moderate to severe injury by the AIS may worsen over the
first few days; therefore, repeat bronchoscopy may be needed.
In addition to age and TBSA, predictors of mortality and prolonged ICU care include severe injury by bronchoscopy, a
decline in PaO2/FiO2 ratio at 48h, decreased pulmonary compliance, pneumonia, and Acute Physiology and Chronic Health
Evaluation II (APACHE II) scores on admission [3, 26–28].
Management
The treatment of inhalation injury, other than carbon
monoxide and hydrogen cyanide, is supportive care after
early recognition, lung protective ventilation strategies,
inhaled/nebulized medications, and bronchoscopy to guide
therapy [15, 25]. Immediate intubation, when indicated, and
avoidance of prolonged mechanical ventilation may prevent
acute and long-term complications.
Chapter 5. Inhalation Injury
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151
Airway Management
Approximately 1/3 of admissions to burn centers with
intubation are extubated promptly, indicating an unnecessary
intubation in the pre-burn center setting [18, 30]. The decision
to intubate should be based on the current airway examination
and not on presumed future sequelae. Routine prophylactic
intubation may cause more harm. There are many risks of
intubation: inability to intubate, unplanned extubation
(inability to secure endotracheal tube [ETT] on burned face),
tracheal trauma, suction-catheter trauma, poor pulmonary
toilet, and ventilator-associated pneumonia [30]. Intubationrelated complications are more common in those intubated in
a pre-burn center setting [18]; however, in hospitals without
burn physicians or those with airway expertise, early intubation may be lifesaving. Stridor and laryngeal edema may
progress rapidly during burn resuscitation in those with signs
and symptoms of inhalation injury.
In patients without overt airway obstruction and difficult
oxygenation/ventilation, supplemental humidified oxygen
should be sufficient while the primary and secondary physical
assessments are completed [1]. Impending loss of the airway
is highly unlikely in those with adequate gas exchange at the
time of initial examination [18]. Although multiple signs of
inhalation injury may be present, the key to success is early
identification of symptomatic patients. The decision to intubate a burn patient with severe stridor (indicating airway
obstruction) is not difficult, but challenges occur in those with
possible inhalation injury, minimal symptoms, and the need
for transport [16].
While conservative management without intubation after
immediate nasopharyngoscopy and bronchoscopy occurs at
many burn centers with anesthesiologists on stand-by, preburn centers should follow guidelines for intubation [31, 32].
Many authors state that large TBSA burns should be intubated irrespective of where the burn occurred as the amount
of resuscitation fluid that they require may lead to edema,
which makes intubation impossible on arrival at the burn
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A. Rodriguez and A. McQuitty
center [30]. In addition to the ATLS intubation guidelines
[11], the Eastern Association for the Surgery of Trauma has
guidelines for emergency intubation in smoke inhalation
patients [33]:
– Airway obstruction
– Severe cognitive impairment (GCS score ≤8)
– Major cutaneous burn (≥40%)
– Major burns and/or smoke inhalation with an anticipated
prolonged transport time
– Impending airway obstruction with moderate-to-severe
facial or oropharyngeal burn or severe airway injury iden-
tified by nasopharyngoscopy and/or bronchoscopy.
Early studies showed that the classic signs of inhalation
injury do not always predict the need for intubation; however,
patients with soot in the oral cavity, facial burns, and large
cutaneous burns should be monitored closely because these
findings indicate a higher likelihood of laryngeal edema and
the need for intubation [34]. Badulak etal. [35] noted that
traditional American Burn Association criteria for intubation
in patients with thermal burns are associated with long-term,
unnecessary intubations; additional signs of injury were
added to create the Denver criteria (Table5.2), which serve
as conservative intubation recommendations for pre-burn
center providers while still reducing unnecessary intubations.
Patients lacking these criteria should be closely monitored
and may avoid intubation. In patients with a questionable
T . Denver criteria
Indications for intubation with thermal burns
• Full thickness facial burns • Altered mentation
• Stridor • Hypoxia/hypercarbia
• Respiratory distress • Hemodynamic instability
• Swelling on laryngoscopy • Suspected smoke inhalation
• Upper airway trauma • Singed facial hair
Source for this table [35]
Chapter 5. Inhalation Injury
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need for intubation, our center utilizes nasopharyngoscopy to
examine upper airway edema and injury.
Although many patients may not require immediate
intubation, it is recommended to contact a burn center in all
patients with suspected inhalation injury. In patients without
signs and symptoms of a compromised airway, burns with a
lower need for pre-transfer intubation are the following [30]:
– Burns that occur from causes other than flame injury
– Burns that do not occur in enclosed spaces
– Burns that are less than 20% TBSA
– Burns that have no full-thickness (third degree) burns to
the face
– Patient is within a reasonable distance to a burn center
(less than 3h).
Patients with severe burns should be presumed to have a
difficult airway, and the medical personnel with the most airway experience should perform the intubation. In centers
without airway expertise (experienced anesthesiologist and/
or otolaryngologist), a multidisciplinary team approach may
be successful; this pre-burn center team may consist of a general surgeon, emergency physician, anesthesiologist, respiratory therapist, and a pre-hospital emergency medical
technician or paramedic. The intubation sequence should follow practice guidelines for management of the difficult
airway by the American Society of Anesthesiology [36]
(https://www.asahq.org) and the ATLS guidelines [11].
Nasotracheal intubation, secured by a septal tie (in those
without facial trauma), is most common in our burn center,
and it may be performed without paralysis and with minimal
sedation [20]. For emergent oral intubation (usually with
videolaryngoscopy assistance), it is crucial to maintain the
ETT security; upper airway edema makes reintubation difficult [37]. Options to secure the ETT include the following:
use of multiple umbilical cotton ties, around the head, above
and below the ears, and tied around the ETT; use of dental
wire around teeth or inserted between the maxilla and teeth,
then the wire is secured around the ETT; placement of a red
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A. Rodriguez and A. McQuitty
rubber catheter through the nose and out of the mouth to
create a loop, and the ETT is tied to the loop with thin cotton
umbilical tape [38]. Less ETT cuff pressure may be needed
due to tracheal edema [39].
There is no evidence to support the routine use of
tracheostomy in burn patients [1]. Tracheostomy should be
avoided initially, as upper airway edema usually resolves in 3–6
days with treatment [15, 40]. With the exception of severe vocal
cord injury, the indications for tracheostomy in this population
are similar to non-burn patients: inability to intubate orally or
nasally, adjunct to head or neck trauma management, airway
protection in high spinal cord or traumatic brain injury, multiple failed weaning trials after prolonged intubation.
Extubation guidelines for burn patients follow conventional
clinical criteria, including airway patency, neurological status,
muscular weakness, pulmonary secretions, and chest
compliance [41]. A positive ETT leak test should be documented prior to extubation. Additionally, our center utilizes
nasopharyngoscopy to identify persistent upper airway
edema, and we often extubate with direct fiberoptic visualization. This is useful in a small subset of patients with large ETT
relative to body size (for example pediatric patients). Securing
a face mask post-extubation for continuous positive airway
pressure may not be possible with facial burns; high flow
nasal cannula is a good alternative [41].
Carbon Monoxide andHydrogen Cyanide
Carbon monoxide toxicity should be suspected in patients
with inhalation injury, especially if the burn occurred in an
enclosed space. Hemoglobin binds carbon monoxide (CO)
with a much higher affinity than oxygen. The formation of
carboxyhemoglobin (COHb) results in reduced oxygen delivery [37]. Patients may have normal pulse oximetry reading.
Standard pulse oximeters use a wavelength also absorbed by
COHb and may have normal to high readings with CO toxicity. For this reason, levels must be assessed by blood sample
Chapter 5. Inhalation Injury
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CO-oximetry. A COHb level is abnormal if >3% in a nonsmoker or >10% in a smoker [19]. Significant toxicity may
still exist with near-normal levels, depending on the blood
sample timing and oxygen administration.
Patients with low COHB toxicity (10–20%) may have
headache, dizziness, abdominal pain, and nausea. With higher
levels, dyspnea and syncope may occur. Hypotension, seizures, coma, and possibly irreversible neurologic injury are
common with levels >50% [42]. Treatment for suspected or
confirmed carbon monoxide poisoning is administration of
high-flow supplemental oxygen for at least 6 h [1, 13]. The
evidence for hyperbaric oxygen therapy is inconclusive, but it
should be considered for those with persistent metabolic acidosis, loss of consciousness, myocardial ischemia, and pregnancy [19, 42].
Inhaled hydrogen cyanide (HCN), produced in many
household fires, may have a synergistic effect with CO. Tissue
hypoxia, lactic acidosis, dyspnea, hypotension, and seizures
may take hours to days to obtain a result. Levels >3mg/L are
potentially lethal, and a level <1 mg/L is considered mild.
Patients with suspected HCN toxicity should be treated, and
this often occurs in the pre-hospital setting. Hydroxocobalamin
is the first-line therapy, given as a standard dose of 5g IV over
15 min. Red discoloration of the skin and urine is common.
Older combination therapy has many side effects but may be
used if hydroxocobalamin is not available. If hydroxocobalamin (Cyanokit™) is not available, a combination of sodium
nitrite (300mg IV) and sodium thiosulfate (12.5g IV) may be
used as a second-line therapy. This combination (Nithiodote™)
has the risks of hypotension and methemoglobinemia [2, 19].
Mechanical Ventilation
Mechanical ventilation (MV) is an additional risk factor for
mortality, indicating severe injury diagnosed by bronchoscopy [23], and prolonged intubation is associated with tra-
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