Airway Fire

An airway fire is combustion of the tracheal tube, drapes or airway tissue in the presence of oxygen or nitrous oxide. It needs three elements: an oxidiser (oxygen, nitrous oxide), a fuel (tube, swabs, drapes, alcohol preparation) and an ignition source (laser, diathermy, fibreoptic light source).

Epidemiology. Rare but devastating. Estimates of several hundred operating theatre fires each year in the United States are imprecise. Most involve the head, neck and upper chest, and open oxygen during sedation. Laser surgery of the airway, tonsillectomy and tracheostomy carry the highest risk.

Risk factors. Oxygen over 30% or nitrous oxide, uncuffed or unprotected plastic tubes, laser use, diathermy near the airway, wet preparation not yet dry, dry swabs and drapes.

Pathophysiology.

Oxygen enriched gas lowers the ignition temperature of plastics. Combustion produces flame, toxic smoke and heat, causing thermal and chemical injury to the airway and lungs, with carbon monoxide and sometimes cyanide poisoning.

A flash, flame or burning smell, popping sound, smoke from the tube, discoloured drapes, sudden loss of ventilation and ventilator alarms. Later: hoarseness, stridor, soot, cough, wheeze, hypoxaemia, facial burns and pulmonary oedema.

Red flags.

• Visible flame in or near the airway.
• Stridor or airway oedema.
• Carboxyhaemoglobin over 10%.
• Lactate over 8 mmol/L (cyanide).
• Haemodynamic instability.

Clinical at the time. Afterwards: bronchoscopy to grade injury and remove debris, chest radiograph, blood gas with co-oximetry (carboxyhaemoglobin), lactate, and CT if deep injury is suspected.

Differential diagnosis.

• Burn from diathermy without airway ignition.
• Chemical pneumonitis.
• Aspiration.
• Laryngospasm.
• Bronchospasm.

Immediate actions (airway fire).

• Stop all gas flow to the airway (oxygen and nitrous oxide), disconnect the circuit and remove the tube.
• Pour saline into the airway if flame persists, and extinguish burning drapes and swabs with saline, water or a carbon dioxide extinguisher.
• Examine the tube for missing fragments and remove debris.
• Ventilate by mask with the lowest oxygen needed for saturation, then reintubate carefully.
• Call for the fire team and evacuate if the fire spreads.

Subsequent care. Bronchoscopy to assess burns and clear debris. Early intubation for oedema or burns. Give 100% oxygen if carboxyhaemoglobin is raised.

• Adrenaline (nebulised, for airway oedema): 5 mg (5 mL of 1 mg/mL) nebulised, repeated once after 20 minutes if needed; maximum 10 mg in this use; monitor heart rate and rhythm; use caution in ischaemic heart disease and tachyarrhythmia.
• Hydroxocobalamin (suspected cyanide toxicity): 5 g IV over 15 minutes, then a second 5 g over 15 minutes to 2 hours by response; maximum 10 g; monitor blood pressure, ECG and urine colour (red); it interferes with co-oximetry and some laboratory tests; children 70 mg/kg (maximum 5 g).

Steroids have no proven benefit. Antibiotics are used only for infection.

Prevention. Use a laser resistant tube with a saline filled cuff, keep inspired oxygen at 30% or less and avoid nitrous oxide near the airway, allow alcohol based preparation to dry for at least 3 minutes, moisten swabs, keep the diathermy tip away from the airway, and brief the team on a fire drill.

Monitoring. Respiratory rate, saturation, carboxyhaemoglobin and lactate, airway oedema, and renal function.

Referral and escalation. Critical care, ENT and burns teams. Report the incident.

Special groups. Children are at high risk of airway oedema. Patients with smoke inhalation need carbon monoxide and cyanide checks.