Myoplasmic Calcium Changes Precede Metabolic and Clinical Signs of Porcine Malignant Hyperthermia

This study examines the chronologic relationship of the biochemical and clinical development of malignant hyperthermia (MH) in susceptible swine. Four pigs previously established by challenge to be susceptible to MH were studied. Monitors included end-tidal CO2 (ETco2), transcutaneous oxygen saturation (Spo2), intraarterial blood pressure, rectal temperature, electrocardiogram (ECG), and train-of-four twitch measurements. Calcium-selective micro-electrodes were used to monitor changes in the concentration of free myoplasmic calcium ([Ca]i). The animals were studied in the resting state, during the development of the syndrome, and after treatment with dantrolene sodium. The increase in [Ca]i preceded the increase in ETco2 that preceded a decrease in Spo2 that preceded the classic first sign, tachycardia, and all preceded the increase in rectal temperature. Dantrolene reversed all of these physiologic changes in the same order of precedence as the increase.