Expansion
Uncontrolled calcium release causes sustained contraction and hypermetabolism
Expansion
Mechanism: an inherited defect of the ryanodine receptor (RYR1), inherited autosomal dominantly. Triggering agents cause uncontrolled calcium release from the sarcoplasmic reticulum, producing:
- Sustained muscle contraction and rigidity, classically masseter spasm
- Massive ATP consumption and heat generation
- Hypermetabolism: rising carbon dioxide, oxygen consumption and lactate
- Rhabdomyolysis with hyperkalaemia and myoglobinuria
Triggers: all volatile anaesthetic agents and suxamethonium. Safe agents include propofol, nitrous oxide, opioids and non-depolarising blockers.
Signs in order: rising end-tidal carbon dioxide (earliest and most sensitive), tachycardia, rigidity, arrhythmia, then hyperthermia, which is a late sign despite the name.
Treatment
- Stop the trigger, use a clean circuit, 100 per cent oxygen and hyperventilate
- Dantrolene 2.5 mg/kg, repeated as needed. It blocks the ryanodine receptor
- Active cooling, treat hyperkalaemia, arrhythmias and acidosis, maintain urine output
Family members require counselling and testing, historically by in vitro contracture testing and increasingly by genetic analysis.