Malignant hyperthermia

Also known as Malignant hyperthermia (MH) · MH crisis · Dantrolene · Ryanodine receptor mutation

Malignant hyperthermia is a pharmacogenetic emergency triggered by volatile anaesthetic agents (sevoflurane, isoflurane, desflurane, halothane) or suxamethonium (succinylcholine). Mutated ryanodine receptor (RYR1) causes uncontrolled calcium release from skeletal muscle sarcoplasmic reticulum → sustained muscle contraction → massive heat production, rhabdomyolysis, hyperkalaemia, acidosis. Presents during or after anaesthesia: rapid rise in end-tidal CO2 (unexplained), tachycardia, masseter spasm, hyperthermia (late sign), rigidity, dark urine (myoglobinuria). Treatment: STOP TRIGGER, hyperventilate with 100% O2, DANTROLENE 2.5 mg/kg IV (repeat to 10 mg/kg), cooling, treat hyperkalaemia/acidosis. Mortality <5% with prompt dantrolene (was over 80% before dantrolene).

low13 referencesUpdated 19 Aug 202621 min readSource-verified · Oct 2026

Checked against its sources on 1 Oct 2026

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12 MCQs

Meet the patient

A fit 24-year-old builder comes in for an elective inguinal hernia repair. Suxamethonium is given for intubation and his jaw clamps shut — masseter spasm the trainee blames on a light dose. Ten minutes later the end-tidal CO2 is climbing despite tripling the minute volume, the heart rate races past 130, and the temperature jumps a degree. That triad is malignant hyperthermia until you prove otherwise.^[5]

The classic trap: waiting for the temperature. Fever is the late sign and the end-tidal CO2 is the early one; dantrolene given before the temperature peaks is the whole game. Hold that rule and the protocol below writes itself.^[1]

References13Show

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