Malignant hyperthermia (MH)
Overview
Malignant hyperthermia is a rare, life‑threatening pharmacogenetic hypermetabolic disorder of skeletal muscle triggered in susceptible individuals by certain anaesthetic agents. In the emergency department an MH crisis is a resuscitation problem: rapid recognition, immediate cessation of triggers, aggressive airway and ventilatory support, active cooling and prompt administration of dantrolene are lifesaving.
Pathophysiology (concise)
Genetic variants (most commonly RYR1; usually autosomal dominant) cause abnormal ryanodine receptor function. Exposure to triggering agents causes uncontrolled release of Ca2+ from the sarcoplasmic reticulum, leading to sustained muscle contraction and hypermetabolism.
The resulting cascade produces rapidly rising CO2 (hypercapnia), metabolic acidosis, lactataemia, rhabdomyolysis with myoglobinuria, hyperkalaemia and risk of acute kidney injury, disseminated intravascular coagulation, compartment syndrome and fatal arrhythmia.
Triggers
- Volatile inhalational anaesthetics such as halothane, isoflurane, sevoflurane and desflurane.
- Depolarising neuromuscular blocker: suxamethonium (succinylcholine).
- Non‑anaesthetic causes (for example heat stroke or exertional rhabdomyolysis) can produce MH‑like pictures but are clinically distinct and are usually not true MH.
Key clinical features
- Earliest and most sensitive sign: unexpected and progressive rise in end‑tidal CO2 (ETCO2) despite increasing minute ventilation; monitor ETCO2 closely in suspected cases.