EFFECTS OF ENFLURANE AND ISOFLURANE IN AIR-OXYGEN ON CHANGES IN THERMAL BALANCE DURING AND AFTER SURGERY

The temperatures in the aural canal (core), skeletal muscleand skin surface were measured during anaesthesia and surgeryin 32 healthy females undergoing total abdominal hysterectomyand for 4 h after operation. The patients were allocated randomlyto one of four groups according to the end-tidal concentrationof volatile anaesthetic: 1 MAC isoflurane, 1 MAC enflurane,1.8 MAC isoflurane and 1.8 MAC enflurane. The lungs were ventilatedwith an air-oxygen mixture. Neuromuscular block was producedwith pancuronium. Room temperature and i.v. fluid administrationwere standardized. Aural canal, muscle and mean skin temperaturesdecreased significantly in all groups during surgery (P <0.001). The decrease in core and muscle temperatures, and meanbody heat was significantly greater in the 1.8 MAC groups thanin the 1 MAC groups for both volatile agents (P < 0.001).However, there was a significantly greater decrease in coretemperature and mean body heat in the isoflurane compared withthe enflurane group (P < 0.026). Body temperature returnedto preoperative values during the recovery period. There wasa significantly greater rate of rewarming during the first 1h of recovery in the 1.8 MAC groups compared with the 1 MACequivalent (P < 0.001), and this was independent of the volatileagent used. The present results are compared with those reportedpreviously in which nitrous oxide was added to the volatileagents. The decrease in body temperature depends upon the concentrationof vapour used. However, it appears that isoflurane, withoutnitrous oxide, caused greater loss of body heat than enflurane.