Smoke Inhalation Injury

Smoke inhalation injury is airway and lung damage from breathing the products of combustion in a fire. It accompanies 20 to 30 percent of major burns and is the major cause of death in fire victims.

Three mechanisms act together:

• thermal injury to the upper airway (the lower airway is protected by reflex closure and heat exchange unless steam is inhaled)
• chemical injury to the tracheobronchial tree and alveoli from irritant gases (aldehydes, acids, ammonia, hydrogen chloride, sulphur dioxide)
• systemic asphyxiation from carbon monoxide and hydrogen cyanide

Domestic charcoal stoves, informal settlement fires, and enclosed space fires are the common settings in Kenya. Injury evolves over 24 to 72 hours with mucosal oedema, sloughing, bronchorrhoea, cast formation, and atelectasis, followed by bronchopneumonia in the second week. Mortality for burns with inhalation injury is roughly twice that of burns without.

• History of enclosed space exposure, loss of consciousness, or facial burns.
• Singed nasal hairs, facial burns, carbonaceous sputum, soot around mouth and nares, hoarseness, stridor, cough, wheeze, drooling.
• Hypoxaemia with a normal SpO2 reading in carbon monoxide poisoning (pulse oximeters read carboxyhaemoglobin as oxyhaemoglobin).
• Headache, confusion, seizures, coma (carbon monoxide, cyanide); cherry red skin is a late and unreliable sign.
• Hypotension, lactic acidosis, and cardiac ischaemia suggest cyanide toxicity.
• Red flags: stridor, voice change, deep neck or facial burns, carboxyhaemoglobin over 25 percent, lactate over 10 mmol/L, SpO2 falling, burns over 20 percent of body surface.

• Clinical diagnosis at presentation; investigations follow resuscitation.
• Co-oximetry on arterial blood: carboxyhaemoglobin (normal below 3 percent, below 10 percent in smokers), methaemoglobin.
• Lactate over 8 to 10 mmol/L with smoke exposure in a fire victim is strong evidence of cyanide poisoning; blood cyanide levels do not return in time to guide treatment.
• Arterial blood gas: metabolic acidosis; PaO2/FiO2 ratio.
• Flexible bronchoscopy: erythema, mucosal oedema, soot, ulceration, necrosis, confirming and grading injury; performed within 24 hours.
• Chest radiograph: usually normal initially; later infiltrates or oedema.
• ECG and troponin for myocardial ischaemia.
• Exclude pneumothorax, other trauma, and the toxic ingestions in a confused patient.

• Airway first: early intubation with the largest tube that fits (8.0 mm or larger in adults to allow bronchoscopy) for stridor, voice change, deep oropharyngeal burns, progressive oedema, or facial burns with soot in airway. Do not wait for stridor.
• Oxygen: 100 percent through a non-rebreather mask or ventilator for at least 6 hours and until carboxyhaemoglobin is below 5 percent; this shortens the carboxyhaemoglobin half life from 4 to 5 hours to 60 to 90 minutes.
• Hyperbaric oxygen at 2.5 to 3 atmospheres for 90 minutes is advised for carboxyhaemoglobin over 25 percent, loss of consciousness, neurological signs, pregnancy with carboxyhaemoglobin over 15 percent, or cardiac ischaemia, if accessible and the patient is stable.
• Cyanide: hydroxocobalamin 5 g intravenously over 15 minutes (children 70 mg/kg, maximum 5 g), repeat 5 g once if shock or severe acidosis persists; give for suspected cyanide toxicity (coma, shock, lactate over 8 mmol/L). Sodium thiosulfate 12.5 g intravenously over 10 minutes (children 400 mg/kg) is the alternative or adjunct; avoid sodium nitrite in the presence of carbon monoxide.
• Bronchospasm: salbutamol 2.5 to 5 mg nebulised every 2 to 4 hours as needed.
• Nebulised therapy for airway cast and bronchorrhoea: heparin 5000 to 10 000 units in 3 mL of normal saline alternating with acetylcysteine 20 percent 3 mL, plus salbutamol 2.5 mg, each every 4 hours for 7 days in intubated patients.
• Ventilation: tidal volume 6 mL/kg predicted body weight, plateau pressure 30 cmH2O or less, therapeutic bronchoscopy for cast removal.
• Fluids: resuscitate for the burn using 2 to 4 mL/kg per percent of total body surface area burn over 24 hours of Ringer's lactate (half in the first 8 hours), titrate to urine output of 0.5 mL/kg per hour; inhalation injury raises requirements.
• Do not give prophylactic antibiotics or steroids; treat pneumonia on culture (ventilator associated pneumonia typically days 3 to 7).
• Follow up: spirometry at 3 months; screen for subglottic and tracheal stenosis, bronchiectasis, chronic cough, and neuropsychiatric sequelae of carbon monoxide up to 3 weeks later.