MYOPLASMIC CALCIUM CHANGES PRECEDE METABOLIC AND CLINICAL SIGNS OF PORCINE MALIGNANT HYPERTHERMIA

This study examines the chronologic relationship of the biochemical an d clinical development of malignant hyperthermia (MH) in susceptible s wine. Four pigs previously established by challenge to be susceptible to MH were studied. Monitors included end-tidal CO2 (ETco(2)), transcu taneous oxygen saturation (Spo(2)), intraarterial blood pressure, rect al temperature, electrocardiogram (ECG), and train-of-four twitch meas urements. Calcium-selective microelectrodes were used to monitor chang es in the concentration of free myoplasmic calcium ([Ca2+](i)). The an imals were studied in the resting state, during the development of the syndrome, and after treatment with dantrolene sodium. The increase in [Ca2+](i) preceded the increase in ETco(2) that preceded a decrease i n Spo(2) that preceded the classic first sign, tachycardia, and all pr eceded the increase in rectal temperature. Dantrolene reversed all of these physiologic changes in the same order of precedence as the incre ase.