Malignant hyperthermia

Learning objectives

Malignant hyperthermia (MH) is caused by genetic defects, most commonly in the RYR1 gene (more rarely affected genes include CACNA1S and STAC3)
Caused by an increase in metabolic rate driven by an increase in intracellular calcium levels in muscle tissue
Can be triggered when exposed to potent inhalation anesthetics and/or succinylcholine

Patients that have a higher risk of MH when exposed to triggering agents:

Any close relative has a confirmed susceptibility to MH
The patient or a close relative has a history of an event that is suspected to be MH during anesthesia
The patient or a close relative has a history of rhabdomyolysis, which can be triggered by exercise in extreme heat and humidity or when taking a statin drug
Patients with another genetic muscle disorder (e.g. Duchenne muscular dystrophy)
Patients with idiopathic hyperCKemia
Patients with otherwise unexplained exertional heat illness

Hyperkalemia may require administration of calcium chloride, sodium bicarbonate, and/ or insulin with glucose
Treat arrhythmias with magnesium, amiodarone or beta-blockers. Avoid calcium channel blockers as they interact with dantrolene, potentiating myocardial depression
Disseminated intravascular coagulation may require blood product transfusion
Rhabdomyolysis may result in acute kidney injury; measure creatine kinase and institute forced alkaline diuresis
Transfer the patient to the ICU once sufficiently stable

The diagnosis of MH is confirmed by muscle biopsy and in vivo contracture testing at specialist centers
The patient and their family members must be followed-up and counseled regarding future anesthetics
An alert should be documented in the patient notes and the patient should consider wearing an alert bracelet or carrying an alert card to notify medical staff of their condition in case of future emergencies

Taking a personal and family history of anesthetic problems is a mandatory part of the preoperative assessment for all patients requiring general or regional anesthesia
Activated charcoal filters should be available at all anesthetizing locations
Patients at increased risk of developing malignant hyperthermia must not be exposed to potent inhalation anesthetics or succinylcholine