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Malignant hyperthermia
Malignant hyperthermia is a genetic reaction of skeletal muscle to halogenated agents and succinylcholine: calcium is released without control, and the early sign is a rise in EtCO2 — not the fever.
Why it matters in the exam
This is a fixed exam topic: what the first sign is, which drugs trigger it and which are safe, the dantrolene dose, how to prepare the anaesthetic machine for a susceptible patient, and what the diagnostic test is. Differential-diagnosis questions also appear — neuroleptic malignant syndrome, thyroid storm, sepsis, phaeochromocytoma and CO2 rise from laparoscopic insufflation.
The disease is inherited as an autosomal dominant trait, most often through a mutation in the ryanodine receptor (RYR1). After exposure there is hypermetabolism: a rise in EtCO2 despite increased ventilation, tachycardia, muscle rigidity or jaw spasm, and then a mixed acidosis, hyperkalaemia, rhabdomyolysis, myoglobinuria, arrhythmias and fever — which sometimes comes late. Without dantrolene the mortality is very high.
Before every anaesthetic the patient is asked about unusual reactions to anaesthesia in himself and in the family, because inheritance is dominant and a first-degree relative of a patient is considered susceptible until proven otherwise. Wherever halogenated agents or succinylcholine are given, a stock of dantrolene and a written protocol must be available. In exam questions a common distractor is to wait for a high fever before starting treatment, or to give a calcium channel blocker for the arrhythmia — two mistakes that can cost a life.
Key points
- Genetic (RYR1), autosomal dominant; triggers: halogenated agents and succinylcholine.
- The early sign: a rise in EtCO2 despite increased ventilation; fever is late.
- Dantrolene 2.5 mg/kg, repeated until settled.
- Hyperkalaemia, acidosis and rhabdomyolysis — supportive and intensive care.
- Diagnosis afterwards by a muscle contracture test and genetic testing.
Summary table
| Step | What is done | Details |
|---|---|---|
| Stop the trigger | Turn off halogenated agents, give no succinylcholine, switch to intravenous anaesthesia | Continue surgery only if it must go on |
| Ventilation | 100% oxygen at high flow (10 L/min or more), increase minute ventilation | Activated charcoal filters on the machine |
| Dantrolene | 2.5 mg/kg IV, repeat until signs settle | Up to 10 mg/kg and even more; then 1 mg/kg every 4–6 hours |
| Supportive care | Cool when the temperature is above 39 degrees, treat hyperkalaemia, maintain urine output | Stop cooling at 38 degrees |
| After the event | Intensive care for at least 24 hours; refer for susceptibility testing | Muscle contracture test (caffeine-halothane) and genetic testing |
In the full version for subscribers
- A simple algorithm
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Sources
- European Malignant Hyperthermia Group, 2015 review; 2021 consensus on peri-operative management of susceptible patients — Management of an acute crisis
- Miller's Anesthesia, 9th edition (2020) — Malignant Hyperthermia and Muscle-Related Disorders
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.