Etiology
Inhalation injury typically results from an obvious exposure to harmful inhaled substances produced by combustion. While the exposure and presence of injury may be clear, many multiple toxic inhalations may occur simultaneously, and are more difficult to discern. Individuals who seem to be similarly exposed may have quite different injuries, owing to the rapidly changing nature of conditions within the site of exposure. Common causative factors in residential fires are heat, inert gases that displace oxygen (e.g., nitrogen, hydrogen, methane), toxic gases (e.g., carbon monoxide, hydrogen cyanide, ammonia, sulfur dioxides), and particulate matter (dust and smoke).[9][10][11] Workplace exposures vary greatly by industry, underlying the importance of a detailed history and acquisition of safety data monitoring sheets for specific substances present at the location of the exposure. The duration and intensity of exposure are also critical factors in determining the severity of the inhalation injury.
Pathophysiology
The pathophysiology of inhalation injury reflects the heterogeneity of inhalation exposures. Broad categories of injury include direct thermal injury, asphyxiation, systemic toxic effects, and direct injury to the airway.[12] Despite extreme temperatures, the dry air present in a fire holds little heat, which is dissipated rapidly in the upper airway. Thus, thermal injury typically occurs only in the uppermost airway, causing edema and airway compromise.[13][14] Steam injuries are the exception, where the tremendous heat capacity of steam overwhelms the ability of the airway to dissipate heat.[15] Simple asphyxia occurs when high concentrations of inert gases displace oxygen. Absorbed tissue asphyxiants such as carbon monoxide and hydrogen cyanide are more pertinent to individuals removed from the exposure, and cause prolonged metabolic effects by disrupting cellular oxygen transport.[12][16] Many other absorbed gases cause systemic toxicity and inflammation. In burn patients, this effect is often compounded by a similar effect from cutaneous burns, leading to high rates of acute respiratory distress syndrome.[17] Additionally, gaseous and particulate matter can cause direct injury to airway cells, leading to bronchoconstriction, edema, epithelial cell death with sloughing, diminished airway clearance, and airway obstruction.[1][12]
Classification
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