Canadian Journal of Anesthesia, Vol 27, 363-369, Copyright © 1980 by Canadian Anesthesiologists' Society

In Vivo and In Vitro Responses to Magnesium Sulphate in Porcine Malignant Hyperthermia

¹ Department of Anesthesiology, University of Texas Medical Branch, Galveston, Texas, 77550 U.S.A. Supported in part by NIH Grant 23875-01

Magnesium sulphate has previously been shown therapeutic in porcine malignant hyperthermia. It was given intravenously in doses of 99 mg·kg^-1 before and 277 mg·kg^-1 after an episode of malignant hyperthermia had been produced by halothane 1.5 percent, in a group of four malignant hyperthermia susceptible swine. Two groups of four additional MH susceptible and MH resistant swine received a constant infusion of magnesium sulphate 10 mg·kg^-1 until approximately 95 per cent depression of foretoe twitch was produced. Four hyperthermia susceptible controls received saline infusions. All were then immediately challenged with succinylcholine 2 mg·kg^-1 and halothane 1.5 per cent. Muscle strips from three other malignant hyperthermia swine were exposed in vitro to magnesium sulphate with and without halothane, and response of twitch tension and contracture were measured. The malignant hyperthermia response to halothane 1.5 per cent was attenuated but not prevented by pretreatment with magnesium sulphate. It did not appear to be therapeutic in this group. Depression of toe twitch by magnesium sulphate was similar in MH susceptible and MH resistant pigs. Pretreatment with magnesium sulphate markedly attentuated the response to a succinylcholine-halothane challenge in MH susceptible pigs. In vitro magnesium sulphate depressed twitch and halothane contracture responses. We conclude that magnesium sulphate is partially prophylactic for the malignant hyperthermia challenge. The mechanism of this response is likely secondary to calcium ion antagonism at multiple sites. The muscle relaxant reponse to magnesium sulphate cannot be used as a diagnostic test for porcine malignant hyperthermia.