Bronchospasm During Anaesthesia

Bronchospasm during anaesthesia is acute narrowing of the lower airways from bronchial smooth muscle contraction, causing wheeze, high airway pressure and falling tidal volume.

Epidemiology. It occurs in about 0.2% to 4% of general anaesthetics, more often in children, smokers and patients with asthma, chronic obstructive pulmonary disease or a recent respiratory infection.

Causes. Airway stimulation by laryngoscopy, tube or secretions at light anaesthesia; aspiration; anaphylaxis; histamine releasing drugs (atracurium, mivacurium, morphine); beta blocker use; desflurane; endobronchial intubation; and pulmonary oedema.

Pathophysiology.

Vagal reflex activation, inflammatory mediator release and direct irritation contract airway smooth muscle. Air trapping causes hyperinflation, raised intrathoracic pressure, reduced venous return and hypotension.

Expiratory wheeze (silent chest when severe), prolonged expiratory phase, shark fin capnography trace, rising peak pressure with a smaller rise in plateau pressure, incomplete expiration with rising end expiratory pressure, desaturation, tachycardia and hypotension.

Red flags.

• Silent chest with falling saturation.
• Hypotension with air trapping.
• Rash, flushing or angioedema (anaphylaxis).
• Sudden unilateral signs (pneumothorax).

Clinical. Exclude tube kink, blockage, endobronchial position and circuit problems by disconnecting the circuit and ventilating by hand with a self-inflating bag. Check blood pressure, rash and tryptase if anaphylaxis is possible.

Differential diagnosis.

• Tube obstruction or kink.
• Endobronchial intubation.
• Tension pneumothorax.
• Pulmonary oedema.
• Aspiration.
• Anaphylaxis.
• Pulmonary embolism.
• Laryngospasm.

Give 100% oxygen, deepen anaesthesia with a volatile agent or propofol, stop the triggering stimulus, and allow time for full expiration (lower rate, longer expiratory time). Disconnect the circuit briefly if hyperinflation causes hypotension.

• Salbutamol: 5 mg nebulised via the circuit, or 4 to 8 puffs (100 microgram each) by metered dose inhaler with spacer, repeated every 20 minutes; IV 250 microgram slowly if inhalation fails, then 5 to 20 microgram/min; maximum 20 mg nebulised in the first hour; monitor heart rate, potassium and lactate; reduce in tachyarrhythmia and ischaemia.
• Ipratropium bromide: 500 microgram nebulised, repeated every 4 to 6 hours; maximum 2 mg daily; monitor for dry mouth and urinary retention; use caution in glaucoma and prostatic enlargement.
• Magnesium sulphate: 2 g (8 mmol) IV over 20 minutes, single dose; maximum 2 g for this indication; monitor reflexes, blood pressure and respiratory rate; reduce in renal impairment (creatinine clearance under 30 mL/min) and avoid in heart block.
• Ketamine: 0.5 to 1 mg/kg IV bolus, then 0.5 to 2 mg/kg/h if needed; maximum 2 mg/kg/h; monitor blood pressure and heart rate; avoid in uncontrolled hypertension; reduce in hepatic impairment.
• Hydrocortisone: 100 mg IV once, repeated every 6 hours for 24 hours if asthma is the cause; maximum 400 mg daily; monitor glucose; benefit is delayed by several hours.
• Adrenaline (severe or refractory): 10 to 20 microgram IV, repeated every 2 to 3 minutes, or infusion 0.02 to 0.1 microgram/kg/min; maximum titrated to effect; monitor ECG and blood pressure; avoid excess in ischaemia. For anaphylaxis give 0.5 mg IM (adults) or 50 to 100 microgram IV in monitored shock.

Consider extracorporeal support in refractory life threatening cases.

Prevention. Optimise asthma before elective surgery, avoid histamine releasing drugs and desflurane in reactive airways, and extubate awake or with lidocaine cover.

Monitoring. Capnography shape, airway pressures, saturation, ECG and blood gas.

Referral and escalation. Senior anaesthetic help and critical care for refractory spasm. Allergy referral if anaphylaxis is suspected.

Special groups. Children need weight based dosing (salbutamol 2.5 mg nebulised under 5 years; magnesium 40 mg/kg IV, maximum 2 g).