Malignant Hyperthermia

Malignant hyperthermia (MH) is an inherited susceptibility of skeletal muscle. In a susceptible patient, exposure to a triggering anaesthetic causes uncontrolled calcium release from the sarcoplasmic reticulum through the type 1 ryanodine receptor, RyR1. Muscle contracture then drives extraordinary aerobic and anaerobic metabolism: oxygen and ATP are consumed, carbon dioxide and acid accumulate, and heat is generated. Muscle-cell injury releases potassium, myoglobin and creatine kinase, creating the later threats of hyperkalaemia, rhabdomyolysis, acute kidney injury, disseminated intravascular coagulation and dysrhythmia. This is a hypermetabolic crisis, not a primary fever. The experienced nurse notices the physiology before the temperature: an unexplained rise in end-tidal CO2 that persists despite increased minute ventilation, with tachycardia, tachypnoea or muscle rigidity. A normal temperature early in the event is not reassuring. If MH is suspected, treatment begins while the team is still confirming the pattern: call for help, stop the triggers, provide 100% oxygen and obtain dantrolene.