Deliberate mild intraoperative hypothermia for craniotomy

Despite enthusiasm for the use of mild hypothermia during neurosurgical procedures, this therapy has not been evaluated systematically. This study examined the feasibility and safety of deliberate mild hypothermia and rewarming.

Thirty patients scheduled for craniotomy were assigned to either a normothermic or mildly hypothermic group. Tympanic membrane temperature was monitored at anesthetic induction, throughout the isoflurane-fentanyl-N2O-O2 anesthetic, and for 18 h postoperatively. Normothermic patients were warmed to 36.5-37.0 degrees C after an initial temperature decrease, and hypothermic patients were cooled to 35 degrees C. In the hypothermic group temperatures were allowed to drift to 34.5 degrees C before rewarming was initiated. Water blankets and convective heating devices were used to cool and rewarm.

The minimum temperature achieved by the hypothermic group was 34.3 +/- 0.4 degrees C. Cooling occurred at a rate of 1.0 +/- 0.4 degrees C/h. Rewarming took place at a rate of 0.7 +/- 0.6 degrees C/h (range 0.1-1.8) in the hypothermic group. Hypothermia did not delay emergence from anesthesia (20 +/- 15 min) compared with normothermia (15 +/- 15 min, P = .45). Mean temperature upon intensive care unit admission was 35.8 +/- 1.0 degrees C for the hypothermic group and 37.1 +/- 0.5 degrees C for the normothermic group (P < 0.0001). The hypothermic patients had more postoperative shivering. From 8 to 18 h postoperatively the temperatures of the two groups were similar except for a slightly greater temperature in the hypothermic patients at 12 h (37.6 +/- 0.5 vs. 37.3 +/- 0.4 degrees C, P = .029).

Although deliberate mild hypothermia is easily achieved intraoperatively, complete rewarming may be difficult to attain during craniotomy with current methods. In addition to the need for determining whether deliberate mild hypothermia confers cerebral protection in humans, the potential risks of the therapy need to be further characterized.