Diagnostics and Therapeutics: Inhalation Injuries
/Inhalation injury results from tissue damage throughout the respiratory tract after inhalation of smoke, heat, or chemicals. Smoke is most common, but exposure to a wide range of chemicals and other irritants may result in inhalational injury. The emergency physician must recognize inhalation injury, and have an expert understanding of its pathophysiology, management and complications. The majority of the post will focus on more standard smoke inhalation injury management, although some information on chemical inhalants and exposure is also covered.
Epidemiology
Exposure to smoke, particularly in the setting of a house fire is the most common cause of inhalation injury. United States fire departments responded to 1.4 million fires in 2020, with some studies quoting over 500,000 emergency room visits annually for burn and inhalation injuries (4). Of those, there are an average of 3500 civilian deaths and 15,200 injuries per year related to fires and smoke inhalation specifically. When considering burn related injuries, increasing cutaneous burn injury is associated with a relatively direct correlation for increased risk of inhalation injury, although inhalational injury itself without cutaneous injury is an independent predictor of mortality (2,3). Because of this, emergency department (ED) physicians need to maintain a high index of suspicion for inhalation injury in the case of any exposure to smoke or fire, especially in closed or small space exposures.
In addition to smoke inhalation injury from fires, many chemical substances can cause inhalation injury as well including but not limited to nitrogen dioxide, ammonia, chlorine, hydrogen sulfide, ammonia, and by-products from rubber and plastic. The number of fatal injuries from chemical inhalation is much lower than for fire exposure and smoke inhalation. For example, one study examining occupational chemical injuries from 2011- 2017 showed a total of 297 fatalities with an average of around 40 fatalities per year (13). On the other hand, non-fatal injuries from chemical inhalation represent a substantial number of ED visits, with one study quoting over 125,000 ER visits in between 2014-2017 (14). Because of this high number of visits, it is important for ED physicians to have a broad knowledge base for treating chemical inhalation injuries as well as fire and smoke related injuries.
Classification & Pathophysiology of Smoke-related Inhalation Injuries
Inhalational injury morbidity and mortality is a complex problem and thought to be due to a combination of injuries. These injury types are often classified into thermal injury from direct heat exposure, local chemical irritation to the lung and airway tissues, and systemic toxicity from inhaled toxins such as cyanide or carbon monoxide (1). Severity of injury, regardless of anatomic location, is dependent on a number of factors such as duration of exposure, ignition source, size of gas particles, and solubility, among others (4).
Upper Airway
Injury to the upper airway, defined as airway structures proximal to the glottis (i.e. above the vocal cords), occurs primarily due to thermal injury, which results in edema, blister formation and ulceration (5). Because inhalational injuries often co-occur with large cutaneous burns, aggressive fluid resuscitation can rapidly worsen upper airway edema making airway management especially challenging. Similarly, cutaneous burns to the external surface of the neck and lower face can contribute to significant edema and airway swelling (6).
Tracheobronchial tree
Injury to the tracheobronchial tree is most often due to direct chemical irritation and toxic effects of chemicals contained in smoke, or those in poisonous gases or liquid acids (4). Due to the rich sensory and motor innervation of the tracheobronchial tree, chemical irritation incites an inflammatory cascade generating neuropeptides and reactive oxygen species, which in turn results in bronchoconstriction, increased vascular permeability and vasodilation (7). In addition, irritation to the bronchial epithelial lining can cause significant damage to and sometimes sloughing of the mucosal lining. This can then lead to secretions and further edema that can occlude smaller airways and further impair oxygen exchange (4). Fantastic images of injury to the main bronchi are noted here, and images of an airway cast of mucus, denuded epithelial cells, and fibrin pulled from an occluded airway during bronchoscopy can be found here (4).
Lung Parenchyma
Damage to the lung parenchyma and alveoli occurs in a less immediate fashion, and ultimately results in impaired oxygenation. A combination of atelectasis, loss of surfactant, and impaired hypoxic vasoconstriction together result in impaired oxygenation. Patients will often present with delayed pneumonia and ARDS-like injury and need to be monitored for this in larger initial injuries and longer hospitalizations (4).
Systemic toxicity
As an important distinction between inhalation injury and cutaneous burns, the emergency physician should be cognizant of the fact that the patient with inhalation injury needs to be treated for both burn injuries and toxicologic complications. The most relevant toxic gas exposure in the patient with inhalation injury are carbon monoxide (CO) and hydrogen cyanide (HCN). The clinical manifestations and management of patients with exposure to these toxins is a separate topic, but there are a few key takeaways to highlight (4):
CO has a 200-times higher affinity for hemoglobin than oxygen, and therefore patients will present with significant hypoxia
for CO, carboxyhemoglobin levels can be measured from venous or arterial blood, and even if a patient is not hypoxic they may require treatment with oxygen or hyperbaric oxygen based on blood levels
exposure to high levels of CO and HCN should be assumed in all patients with smoke exposure, especially for fires in enclosed spaces
HCN should be suspected in patients with significantly elevated lactate levels (> 8 mmol/L), or in patients with hypoxia unresponsive to oxygen therapy and patients who have alterations in mental status
HCN should be treated with cyano-kits (contain hydroxocobalamin) or a more traditional cyanide antidote kit which contains amyl nitrate + sodium thiosulfate + sodium nitrite
Chemical Inhalation Injuries
Chemical inhalation can result in injury to the respiratory system, and most frequently occurs with accidental exposure in the occupational settings. Individuals working in chemical and petroleum manufacturing, waste management, natural gas, and rubber and asphalt manufacturing are at highest risk for exposure. There are several particular chemicals that cause injury more frequently. Below includes a non-exhaustive list of some common culprits. As a general theme, these agents tend to irritate mucous membranes and the respiratory tract. Management is often centered around decontamination, supportive care, and ARDS ventilation strategies, as necessary when intubation is required.
inhalational injury mechanisms and management (15, 16)
Evaluation
History and Physical Exam
Given that severity of inhalation injury can vary widely and depends on several historical factors, signs and symptoms can vary widely. Like all emergency department patients, the evaluation of patients with suspected inhalation injury should focus on rapid evaluation of airway, breathing and circulation, as well as a detailed history. There are several points of a focused history that are important to obtain including but not limited to:
exposure to fire, smoke, or chemical fumes
exposure in an enclosed space
history of loss of consciousness
Certain physical exam findings that should raise your suspicion of significant airway injury include but are not limited to:
face, lip, and neck burns
soot noted on face or in oropharynx on general examination
singed nasal hairs or facial hair
ongoing coughing, stridor, or voice hoarseness
cyanosis
neurologic deficits
As airway edema and inflammation progress after the time of injury, patients may also complain worsening dyspnea with lung examination revealing increased work of breathing, accessory muscle use, wheezing, and rales on auscultation (7).
While smoke exposure is most common, exposure to steam and other noxious gases are rarer causes of inhalation injury. There is not significant data to guide management of patients with inhalation injury due to other exposures. These patients are typically managed in a similar fashion to those with smoke exposure.
Labs and Imaging
While the clinical evaluation and direct visualization of the airway in inhalation injury is the most important part of the work-up, laboratory and imaging studies remain an important component of the work-up as well in the ER. Testing can include but is not limited to:
standard labs such as CBC, BMP, lactate, VBG
carboxyhemoglobin level, methemoglobin level
cyanide level
Chest imaging, whether with plain radiographs or with computed tomography, is typically not helpful in making the diagnosis of inhalation injury. Chest radiographs are often initially normal, and in fact the presence of opacities on initial chest radiograph is a poor prognostic indicator (4).
Nasopharyngoscopy
Evaluation of the upper airway for signs of inhalation injury can be performed at bedside by nasopharyngoscopy, simultaneously facilitating passage of an endotracheal tube via awake fiberoptic intubation should securing the airway be necessary. A detailed explanation of the procedure is beyond the scope of this article, but in short, successful nasopharyngoscopy relies on several key procedural steps:
Prepare the patient
If time allows, explain the reason for nasopharyngoscopy and steps involved to the patient
Consider anti-sialogogues such as Glycopyrrolate 0.2 mg IV
Anesthetize the airway with viscous or nebulized lidocaine
Consider anxiolysis such as Midazolam 1-2 mg IV or Ketamine 10-20 mg IV
Prepare the equipment
Fiberoptic scopes come in a variety of sizes (Ultraslim 2.8mm, Slim 3.8 mm, Regular 5.0 mm, and Large 5.8 mm), smaller scopes are generally better tolerated and easier to manipulate while larger scopes allow for passage of endotracheal tubes
Consider subtotal intubation for patients with high likelihood of respiratory failure, a 6.0 endotracheal tube is the smallest that will fit over a Large 5.8 mm endoscope
Prepare the team
Before beginning the procedure, the entire team should be aware of the goal of the procedure, either diagnostic or potentially therapeutic (fiberoptic intubation)
If preparing for potential intubation, induction agents and paralytics should be prepared and ready to administer
While performing nasopharyngoscopy, a number of potential findings may point toward inhalation injury. Common findings in the upper airway include tracheal soot, vocal cord and arytenoid edema, and mucosal injury. There does exist grading criteria for findings from nasopharyngoscopy and bronchoscopy, although the formal criteria is less often used than general clinical gestalt. Pictured here are photos from nasopharyngoscopy and bronchoscopy with varying pathology which can be found in the caption.
Left: nasopharyngoscope image notable for soot throughout posterior oropharynx and on arytenoids and true and false vocal cords with edema of arytenoids and true vocal cords. Right: follow up bronchoscopy of the patient once intubated and admitted to the ICU revealing mild erythema to bronchus mucosal tissue.
To intubate or not…?
Resuscitation of the patient with inhalation injury can be complicated and the emergency physician should be aware of several special considerations unique to the burned airway. Recent literature has called into question the frequency with which patients with inhalation injury are intubated in the emergency department. There are data to suggest that a large proportion of patients transferred to burn centers with inhalation injury are intubated unnecessarily. Despite traditional teaching, patients with facial burns and singed nasal hairs alone do not necessarily require immediate intubation. Several key examination findings can help to delineate those patients that do require intubation:
stridor or new hoarseness
respiratory distress or accessory muscle use
blisters or severe edema in the oropharynx
deep burns to the lower face or neck
The approach to airway management in the patient with inhalation injury is a topic all its own. However, those requiring intubation should be intubated promptly by the most experienced operator available prior to burn center transfer. As mentioned in the nasopharyngoscopy above, the ED physician with a high suspicion of airway injury can prepare for intubation over NP scope when setting up for direct visualization with NP scope, to facilitate quick management of the airway. It is also critical to be prepared for a surgical approach in the event of a “can’t intubate, can’t ventilate” scenario (9).
Supportive Care in the Intubated Patient with Airway Injury
After a secure airway has been established, supportive care in the emergency department should be centered on supporting oxygenation and hemodynamics.
For patients in whom there is any concern for CO toxicity, supplemental oxygenation with an Fi02 of 100% (or as close as possible in the non-intubated patient) should be provided.
While patients with inhalation injury often have coexisting cutaneous burns, fluid resuscitation should be approached with caution as over resuscitation can worsen airway edema and obstruction, as well as pulmonary edema impairing oxygenation.
Bronchoconstriction is common and should be treated aggressively with inhaled ß-agonists
Ventilator management should focus on lung-protective ventilation strategies with low tidal volumes and attempt to limit plateau pressures
For patients with significant airway secretions impairing oxygenation, N-acetylcysteine can be used for airway clearance. (7, 10, 11)
Disposition
Disposition of the patient with inhalation injury depends on a number of factors, namely the severity of injury and requirement for intubation. However, inhalation injury alone is an indication for transfer to a burn center. The majority of patients will typically require admission and observation at the very least (12), even if intubation is not performed.
Summary
Inhalation injury requires expert management and can portend significant morbidity and mortality. Management will often include transfer to a burn center, and emergency department care should occur in conjunction with the burn surgery service, when possible. A large portion of patients need supportive care, oxygenation, and observation. However, when more definitive management of the airway is indicated, this should be done quickly and carefully, often with use of nasopharyngoscopy. Systemic toxicities such as carbon monoxide and cyanide poisoning should also be considered when managing inhalation injuries patients.
POST BY Brett Boggust, MD
Dr. Boggust is a PGY-1 in Emergency Medicine at the University of Cincinnati
EDITING BY Thomas Haffner, MD and Anita Goel, MD
Dr Haffner is a PGY-4 in Emergency Medicine at the University of Cincinnati
Dr. Goel is an Assistant Professor in Emergency Medicine at the University of Cincinnati and assistant editor of TamingtheSRU.com
Cite As: Boggust, B., Haffner, T., Goel, A. Diagnostics and Therapeutics: Inhalation Injuries. TamingtheSRU. www.tamingthesru.com/blog/diagnostics-and-therapeutics/inhalation-injuries. 2/28/2025.
references
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