Malignant hyperthermia.

Abstract

Malignant Hyperthermia (MH) has been a recognized complication of general anesthesia after the first case reports in the 1940's. Since then a great deal has been discovered about the genetics, pathophysiology and treatment of this once fatal syndrome. MH is the only clinical entity specifically related to and caused by anesthetic agents. MH once triggered during anesthesia results in a profound hyper metabolic state with rise in the core temperature, increased carbon dioxide production and oxygen consumption. Death will ensue if specific treatment is not started. The incidence of fulminant MH ranges from 1:62,000 to 1: 84,000 of general anesthesia cases if succinylcholine and inhalation agents are used. Massseter muscle spasm on induction of anesthesia, with an incidence of between 1:16,000 and 1:4,000, may be a predromal indication of the development of MH. Anesthetic agents, which may trigger MH in susceptible individuals, are the depolarizing muscle relaxant, succinyl choline and all the volatile anesthetic gasses. Nitrous oxide, intravenous induction agents, benzodiazepines, opioids, and the non-depolarizing relaxants do not trigger MH. MH susceptibility is associated with certain disorders, such as Duchene muscular dystrophy, and triggering agent should not be used in these patients. Inheritance is an autosomal dominant trait with variable penetrance. The pathogenesis of MH involves the loss of control of intracellular calcium ions in skeletal muscle with resultant protracted spasm and hyper metabolism. Clinically this will progress to hypercarbia, hypoxia, hyperthermia, hyperkalemia and death will result if specific treatment is not started. Management involves immediate discontinuation of the triggering anesthetics, hyperventilation with 100% oxygen and most importantly the definitive treatment with intravenous dantrolene.The importance of instigating the use of dantrolene in cases of MH cannot be overemphasized. MH is now treatable when once it would be fatal before the availability of dantrolene. Unless of an emergent nature, surgery should be canceled following the acute phase of MH. The patient should be admitted to intensive care for at least 24 hours and dantrolene continued as recurrence has been described. It is imperative that the patient and their family are counseled, Medalert bracelets provided and registration with the Malignant Hyperthermia Association of the United States (MHAUS), encouraged. The caffeine/halothane testing of muscle biopsies is currently the most definitive test for malignant hyperthermia susceptibility. The routine use in suspected cases or the immediate family of known cases remains a matter of contention.