[Calcium inhibitors and anesthesia]

[Screening tests for malignant hyperthermia susceptibility]

The ideal screening test for malignant hyperthermia susceptibility (MHS) has yet to be discovered. It should be simple noninvasive, yet totally specific and sensitive. Until such an ideal test becomes available, allowing simple routine preoperative screening, tests should only be used in certain specific situations. These include: patients in whom a clinical crisis was suspected; the members of the family of a subject labeled MHS because of a fatal, or otherwise, crisis, or in whom tests were positive; patients with other pathological conditions which could be linked to malignant hyperthermia (MH) (some myopathies, effort or stress MH, neuroleptic malignant syndrome). The various tests proposed in the literature aim at revealing MHN subjects, using or not a triggering agent, halothane most often. However, detecting these abnormalities sometimes gives greater insight into the physiopathology of MH than in the detection of an individual patient's susceptibility. The tests have been classified as in vivo, electrophysiological, blood, and in vitro muscle biochemical, morphological, and pharmacological tests. The discovery of new tests gives renewed hope: CPK levels, platelet tests, calcium sarcoplasmic reticular reuptake, lymphocyte Quin 2 test, nuclear magnetic resonance spectroscopy. However, experts worldwide agree that the only reference test to this day remains the in vitro halothane caffeine contracture tests. These tests have shown their reliability; they must be performed on muscle strips obtained from surgically removed muscle biopsies, by laboratories used to this technique and who have at their disposal a sufficiently large group of MHS subjects with a clear-cut clinical crisis, as well as controls. The patients must therefore travel to these laboratories. The design of common protocols for European laboratories on one hand, and the North American laboratories on the other, is a good guarantee of the reliability of these tests.

[Treatment of malignant hyperthermia crisis during anesthesia]

Malignant hyperthermia (MH), triggered by anaesthesia, is a rare and potentially fatal condition. It requires immediate and specific treatment. This review focuses on anticipation and organisation of treatment. Anticipation means that dantrolene should be available, that an anaesthetic machine should be kept free from all vapours of halogenated anaesthetics, and methods of cooling should be planned. A prompt availability in all operating theatres of dantrolene and the required machines is emphasized. Treatment of a MH episode includes stopping the administration of triggering agents, administering dantrolene, correcting metabolic and respiratory acidosis, and cooling. Different aspects of the cardiovascular pharmacology of dantrolene are discussed. Other drugs are seldom required if proper treatment is started soon enough after the crisis. Complications may arise during a fulminant episode. They are difficult to treat, and may lead to sequelae. A rational approach to the treatment of hyperkalaemia, circulatory and renal failure is discussed. After the crisis, dantrolene should be continued for a short time. Finally, the nonspecific signs which can give the earliest diagnosis possible of MH are discussed: an early diagnosis and early treatment with dantrolene are essential in reducing the mortality of malignant hyperthermia.