Study of two devices used to maintain normothermia in rats and mice during general anesthesia.

Rodents are very susceptible to hypothermia during anesthetic events because of their high body surface-to-mass ratio. This study examined the effectiveness of 2 heating devices, a heatpad and a circulating hot-water blanket, during 60 min of isoflurane general anesthesia in rats and mice (n = 6 per treatment). In addition, 1 control group of animals for each species was anesthetized with no heat source (n = 6). Both devices carried minimal risk of causing thermal burns or hyperthermia. Rats on the circulating water blanket showed a slight decrease (0.11 +/- 0.19 degrees C) from the initial (time 0) body temperature (mean +/- standard error), whereas the heatpad was associated with a significant increase (0.96 +/- 0.10 degrees C). Mice on the circulating water blanket showed a significant decrease (0.46 +/- 0.05 degrees C) in body temperature. The trend in mice on the heatpad was similar to that in rats, with a significant increase (0.94 +/- 0.13 degrees C) from the body temperature at time 0. Although statistically significant, these deviations from baseline body temperature were not considered physiologically relevant. In comparison, body temperatures decreased significantly in rats and mice (4.42 +/- 0.60 and 9.90 +/- 0.35 degrees C, respectively) with no heat source. Both heating devices were safe and effective, but the low cost, ease of maintenance, and portability of the heatpad may make it a more desirable choice in some facilities.