THERMAL RESPONSE IN ACUTE PORCINE MALIGNANT HYPERTHERMIA

This study was designed to evaluate how vital organ and skin-surface t emperatures correlate with other clinical signs of a malignant hyperth ermia (MH) episode. Six susceptible swine were anesthetized with thiop ental and nitrous oxide and kept normothermic (approximate to 38 degre es C). After a 30-min control period, halothane (1 minimum alveolar an esthetic concentration) was administered, followed in 5 min by a bolus of succinylcholine (2 mg/kg intravenously). Monitoring included: 1) E Tco(2); 2) Pao(2), Paco(2), pH(a); 3) cardiovascular function; 4) core temperatures (esophagus, pulmonary artery, and rectum); 5) organ temp eratures (brain, kidney, liver, and four skeletal muscles); and 6) ski n temperatures (forehead, neck, and axilla). Within 10 min after expos ure to halothane and succinylcholine, all animals developed fulminant MH. Kidney, liver, and brain temperatures increased more rapidly than pulmonary artery temperature with the onset of MH. Temperatures signif icantly increased in the visceral organs prior to the detection of con tractures within skeletal muscles. The masseter, longissimus dorsi, qu adriceps, deltoid, and extensor digiti II intramuscular temperatures w ere 1-2 degrees C less than pulmonary artery and esophageal temperatur es during the episodes, whereas those of the kidney, liver, and brain were the same or slightly greater. When it occurs, core hyperthermia d uring acute MI-I results largely from heat produced in central organs, not in skeletal muscle per se. In these swine, changes in axilla skin surface temperatures correlated well with core temperature trends, wh ereas those of the neck and forehead did not. Unless a skin-surface pr obe can be placed in close proximity to a major vessel, cutaneous temp eratures should not be substituted for measurements at an appropriate core site.