Succinylcholine-Induced Hyperkalaemia

Succinylcholine induced hyperkalaemia is an abnormal potassium rise after depolarising block. Normal patients show a rise of 0.3 to 0.5 mmol/L. In susceptible patients, potassium can rise by 5 to 10 mmol/L within minutes, causing arrhythmia and cardiac arrest.

Epidemiology. Rare but potentially fatal. The classic cases include undiagnosed muscular dystrophy in boys (especially Duchenne), where rhabdomyolysis and hyperkalaemic arrest occurs.

At risk conditions.

• Burns, crush injury and major trauma, from about 24 to 72 hours after injury and for months.
• Denervation: spinal cord injury, stroke with hemiplegia, motor neuron disease, Guillain-Barre syndrome, prolonged neuropathy.
• Prolonged immobilisation or critical illness myopathy.
• Muscular dystrophies and myopathies.
• Severe intra-abdominal infection and tetanus.
• Pre-existing hyperkalaemia, acidosis and renal failure.

Pathophysiology.

Prolonged denervation or injury causes proliferation of extrajunctional acetylcholine receptors (including the fetal alpha-7 type) across the muscle membrane. Succinylcholine opens these channels, producing massive potassium efflux.

In dystrophy, the fragile membrane allows rhabdomyolysis, which adds release of intracellular potassium.

Peaked T waves, widened QRS, loss of P waves, sine wave pattern, bradycardia, ventricular fibrillation or asystole, usually within 1 to 5 minutes of injection. Arrest in a child after succinylcholine should be assumed to be hyperkalaemia until proven otherwise.

Red flags.

• Abrupt ECG change or arrhythmia after injection.
• Arrest in a child or adolescent after succinylcholine.
• Dark urine and rising creatine kinase.

Blood gas with potassium urgently. ECG shows peaked T waves, flattened P waves, widened QRS or sine wave. Measure creatine kinase, creatinine, urea and calcium. Review history for burns, immobilisation, neuromuscular disease or recent trauma. Consider dystrophin testing or neurology review after recovery in children.

Differential diagnosis.

• Malignant hyperthermia.
• Anaphylaxis.
• Air embolism.
• Hypoxic arrest.
• Local anaesthetic toxicity.
• Pre-existing hyperkalaemia.
• Tension pneumothorax.
• Dilutional or transfusion related hyperkalaemia.

Arrest. Start cardiopulmonary resuscitation and use the advanced life support algorithm. Give calcium early, hyperventilate with 100% oxygen, and prolonged resuscitation is justified because recovery is common.

Drug treatment.

• Calcium chloride 10%: 10 mL (1 g) IV over 2 to 5 minutes; repeat every 5 minutes while ECG changes persist; maximum 3 doses before reassessment and in arrest as clinically needed; monitor ECG and ionised calcium; extravasation risk so use a large vein or central line; use caution with digoxin.
• Soluble insulin with glucose: 10 units IV with 25 g glucose (50 mL of 50% glucose) over 15 minutes; repeat if potassium remains high; monitor glucose hourly for 6 hours; use 5 units in renal impairment.
• Salbutamol: 10 to 20 mg nebulised over 10 to 15 minutes, or 0.5 mg IV slowly; repeat as needed; monitor heart rate and potassium; avoid in tachyarrhythmia and use caution in ischaemia.
• Sodium bicarbonate 8.4%: 50 mmol (50 mL) IV over 5 minutes if pH under 7.2 or with prolonged arrest; repeat once; maximum 100 mmol in this setting without blood gas; monitor sodium, pH and potassium; caution with fluid overload.
• Furosemide: 40 to 80 mg IV; once, repeated by response; maximum 200 mg daily; monitor urine output and electrolytes; use caution in hypovolaemia and anuria.

Definitive. Haemodialysis or haemofiltration for refractory hyperkalaemia, renal failure or rhabdomyolysis. Cardiopulmonary bypass or extracorporeal support for prolonged arrest where available. Stop volatile agents in suspected dystrophy and use total intravenous anaesthesia.

Prevention.

• Avoid succinylcholine in at risk conditions.
• Use rocuronium 1.0 to 1.2 mg/kg IV for rapid sequence induction with sugammadex 16 mg/kg available; maximum sugammadex 16 mg/kg; confirm train-of-four ratio 0.9 or more; avoid sugammadex if creatinine clearance is under 30 mL/min.
• Avoid succinylcholine in boys under 8 to 10 years unless airway emergency.

Monitoring. Continuous ECG, potassium every 15 to 30 minutes until stable, creatine kinase, creatinine, urine output and urine myoglobin.

Referral and escalation. Critical care and nephrology for refractory hyperkalaemia or rhabdomyolysis. Neurology and genetics for suspected dystrophy, and counselling of the family.