Hypothermia and electromagnetic rewarming in the rhesus monkey

Five male rhesus monkeys (Macaca mulatta) were subjected, under ketamine anesthesia, to repeated hypothermia treatments that produced an average rectal temperature of 28.3 degrees C. Following hypothermia induction, the subjects were rewarmed using either a ventrally applied surgical heating pad supplied with 35 degrees C water or a radio-frequency (RF) induction coil operating at 13.56 MHz with an average specific absorption rate (SAR) calculated to be approximately 5.5 W X kg-1. A special temperature probe, nonperturbing to RF, was used in the RF rewarming experiments. Control experiments were also conducted in which only ketamine was administered over a 3-h period. RF rewarming to 35 degrees C typically required only 50 min; whereas, an average of 137 min was required for heating-pad rewarming. Analyses of blood serum collected during and up to 48 h after hypothermia treatments showed elevations at 24 h in creatine phosphokinase (CPK), lactic dehydrogenase (LDH), and glutamic oxaloacetic transaminase (GOT), and these elevations were highest for the ketamine controls and lowest for the RF rewarming experiments. The subjects have been periodically examined since these experiments, and all appear to be in good health. It is concluded that the careful application of RF energy to the central core of the body can successfully be used for rewarming purposes, is more effective than externally applied rewarming techniques, and is potentially useful in remote locations.