Malignant Hyperthermia (MH)

Clinical Features

Malignant Hyperthermia (MH) is a severe adverse reaction to commonly used anesthetics (halothane, sevoflurane, desflurane, enflurane, isoflurane) or to depolarizing muscle relaxants (succinylcholine) (Nelson and Flewellen N Engl J Med 309:416-418, 1983; Larach et al. Anesth Analg 110:498-507, 2010; Rosenberg et al., 2010). In susceptible patients these agents may trigger uncontrolled muscle hypermetabolism. In almost all cases, the first manifestations of MH occur in the operating room. Death can result unless the patient is promptly treated (Larach et al. Anesthesiology 108:603-611, 2008).


Knowledge of susceptibility is the key factor to avoid the morbidity/mortality associated with MH. Susceptibility may be determined by either a muscle biopsy test (sometimes called the in vitro muscle contraction test) or by DNA testing. The muscle biopsy test is more sensitive than DNA testing, but is expensive, painful, and requires travel to one of a few biopsy centers. DNA testing is not as sensitive, but has the advantages of being relatively low cost and requiring no travel (blood specimens are transported to the testing labs). DNA testing has the further advantage that once the causative mutation is identified in a proband, then other family members can be tested much more easily than with the muscle biopsy test.

Avoidance of Triggering Agents

Avoidance of the triggering agents (listed above) appears to be an almost completely effective means of preventing MH. Although somewhat more expensive and more difficult to administer, alternative anesthetics are available for patients at risk for MH (Wappler Current Opinion in Anesthesiology 23(3): 417-422, 2010). It is recommended that medical alert bracelets or other alert devices be worn by susceptible individuals to aid emergency room personnel (Malignant Hyperthermia Association of the United States, 2013;


Sodium dantrolene has been shown to be an effective antidote to the triggering agents and has dramatically reduced the number of deaths due to MH (Harrison Br J Anaesth 81:626-629, 1998; Anderson and Jones Anesthesiology 44(1):57-61, 1976). These days, most surgical suites in developed nations stock dantrolene. However, since non-fatal MH events are still often accompanied by significant morbidity (Larach et al. Anesth Analg 110:498-507, 2010), they should be avoided through the use of alternative anesthetics. Calcium channel blockers should not be given together with dantrolene because of the risk of life-threatening hyperkalemia (Rosenberg et al., 2010).

Heat and Strenuous Exercise

There have been a few reports of MH events triggered by heat and/or strenuous exercise (Groom et al. Anesthesiology 115:938-945, 2011; Tobin et al. JAMA 286:168-169, 2001). Susceptible individuals may therefore want to avoid excessive exertion in hot weather. For susceptible individuals undergoing cardiac bypass surgery, aggressive rewarming should be avoided, as it may be associated with development of clinical signs of MH (Rosenberg et al., 2010).

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This article is a summary of information that has been reported in the biomedical research literature. It is not medical advice for patients. All disease treatments should be under the direction of a qualified healthcare provider.