Inhalation injury

Inhalation injury refers to damage to the respiratory tract and lungs caused by the inhalation of harmful substances such as smoke, gases, vapors, fumes, chemicals, dusts, mists, aerosols, or airborne particles.

Thermal injuries typically affect the upper airway due to heat dissipation and protective reflexes, while chemical irritants in smoke damage both the upper and lower airways. This damage leads to mucosal sloughing, inflammatory mediator release, impaired mucociliary clearance, airway obstruction, and pulmonary edema. Systemic toxicity from inhaled CO and cyanide exacerbates hypoxia by impairing oxygen transport and metabolism, potentially resulting in early mortality. Within 12-48 hours, necrotizing bronchitis, airway swelling, and pulmonary edema may cause respiratory failure, with increased susceptibility to infections due to epithelial necrosis. Chemical inhalation injury involves damage to the respiratory system through direct cellular interactions or alterations in the cellular microenvironment. Respiratory irritants, depending on their water solubility, liberate acids, alkali, and oxidants, triggering inflammatory cascades and damaging mucous membranes. Exposure to specific agents like metal fumes, hard metal dusts, and fluorocarbon breakdown products induces immunological and inflammatory responses through antigen-antibody complex formation, cytokine release, and neutrophil activation. Asphyxiant agents exacerbate hypoxia, with systemic asphyxiants interfering with oxygen transport and utilization, causing metabolic acidosis and hyperlactatemia. Vesicants, including sulfur mustard and lewisite, inflict irreversible tissue damage through cytotoxic mechanisms, oxidative stress, and enzyme inhibition, potentially leading to severe lung inflammation, respiratory failure, and systemic toxicity.

Inhalation injury is present in 10-20% of patients with burn injuries.

Risk factors for inhalation injury include pediatric or advanced age, history of smoking, cardiac and respiratory comorbidities, loss of consciousness, and prolonged exposure.

Patients often present after exposure to fire and smoke in an enclosed space, frequently accompanied by cutaneous burn injuries. Symptoms of supraglottic thermal injury include facial or neck burns, singed facial or nasal hair, stridor, and oropharyngeal erythema, edema, or blistering. Subglottic and alveolar chemical injuries may present with cough, wheezing, dyspnea, hoarseness, carbonaceous sputum, increased secretions, altered consciousness, and accessory respiratory muscle use. Signs of CO or cyanide poisoning may also be present following exposure. Respiratory complications can include progressive airway edema, mucopurulent membrane production, membranous tracheobronchitis, hemorrhage, bronchoconstriction, atelectasis, pneumonia, and ARDS.

The mortality rate in patients with burn inhalation injury is reported at 10-30%.