Succinylcholine-Induced Bradycardia

Succinylcholine induced bradycardia is sinus bradycardia, junctional rhythm, or asystole following succinylcholine, caused by stimulation of cardiac muscarinic receptors.

Epidemiology. It occurs most often in children after the first dose and in adults after a second dose given 3 to 8 minutes after the first. Asystole is rare but reported, particularly in young children and with high vagal tone.

Risk factors. Repeat dosing, children under 5 years, high vagal tone, concurrent opioid, beta blockade, dexmedetomidine, neostigmine, halothane, laryngoscopy stimulation, hypoxia and hypercarbia, and traction on the peritoneum or eye.

Pathophysiology.

Succinylcholine acts as an agonist at muscarinic receptors in the sinoatrial node. Its metabolite succinylmonocholine sensitises these receptors, so a second dose causes greater effect.

Hyperkalaemia, hypoxia and vagal reflexes add to the bradycardia.

Fall in heart rate within 1 to 3 minutes of injection, sinus pauses, nodal rhythm, hypotension and, rarely, asystole. Signs of hypoxia may coexist.

Clinical and by ECG, with confirmation of rhythm and exclusion of other causes: hypoxia, hypercarbia, vagal stimulation, high spinal, drug interaction, hyperkalaemia and raised intracranial pressure. Check oxygenation and end tidal carbon dioxide, and consider blood gas.

Differential diagnosis.

• Hypoxia.
• Vagal reflex from laryngoscopy, traction or peritoneal insufflation.
• Hyperkalaemia.
• Drug effect from dexmedetomidine, opioids or neostigmine.
• Anaphylaxis.
• Raised intracranial pressure.
• Conduction disease.

Treatment. Stop stimulation, ensure oxygenation and ventilation, and give an anticholinergic.

• Atropine: 500 microgram IV in adults, repeated every 3 to 5 minutes; maximum 3 mg; in children 20 microgram/kg IV (minimum 100 microgram, maximum 500 microgram in a single dose); monitor heart rate and rhythm; use caution in glaucoma and tachyarrhythmia.
• Glycopyrronium: 200 to 400 microgram IV in adults or 5 to 10 microgram/kg in children; repeat once if needed; maximum 800 microgram in adults; monitor heart rate; less crosses the blood brain barrier; reduce in renal impairment.
• Adrenaline (refractory): 10 to 20 microgram IV boluses (1 to 2 microgram/kg in children) or infusion 0.02 to 0.1 microgram/kg/min; titrate to heart rate; monitor blood pressure and ECG; avoid excess in ischaemia.

If asystole occurs, start cardiopulmonary resuscitation and give adrenaline 1 mg IV (10 microgram/kg in children). Consider hyperkalaemia and give calcium if ECG suggests it.

Prevention.

• Give atropine 10 to 20 microgram/kg before the first dose in young children, and before any repeat dose in all ages.
• Avoid repeat succinylcholine within 5 minutes without atropine.
• Use rocuronium where suitable.
• Ensure good oxygenation before laryngoscopy.

Monitoring. Continuous ECG, pulse oximetry, blood pressure and capnography until heart rate returns to baseline.

Referral and escalation. Senior anaesthetic help for asystole, recurrent bradycardia or suspected conduction disease. Cardiology review if bradycardia persists after the drug has worn off.

Special groups. In heart transplant recipients atropine is ineffective, so use adrenaline or isoprenaline.