Malignant hyperthermia is a rare, pharmacogenetic complication of general anaesthesia that results from an abnormal increase in muscle metabolism in response to all potent inhalational agents and suxamethonium. There is often a family history of death or major problems associated with anaesthesia. There is excessive metabolic activity in the muscle causing acidosis, heat production and muscle stiffness.

The signs include an abnormal response to suxamethonium (masseter spasm), tachycardia, peripheral cyanosis, muscle stiffness and a high temperature. The patient may develop a mixed acidosis (respiratory and/or metabolic) hyperkalaemia and hyperglycaemia.

Treatment is to discontinue the trigger agent(s), hyperventilate with 100% O2 and administer intravenous dantrolene until the reaction and hyperthermia are controlled. Patient should also require supportive measures such as intravenous fluids, beta blockers, treatment of hyperkalaemia and monitoring in ICU afterwards.