Duration of thermal support for preventing hypothermia induced by anesthesia with medetomidine-midazolam-butorphanol in mice

Hypothermia during anesthetic events is a common adverse effect of anesthesia in laboratory animals. In particular, small rodents such as mice is susceptible to hypothermia during anesthetic events. Therefore, the animals will need additional thermal support by external heating devices during and after anesthesia. In general, the time of recovery from anesthesia is typically longer in case of injectable anesthesia rather than inhalant anesthesia. However, the durations of thermal support have been almost limited to 1 hr from administration of anesthesia in general. Our study objectives are two-fold: 1) to compare the levels of hypothermia induced by injectable anesthesia with medetomidine-midazolam-butorphanol (MMB) and inhalant anesthesia with isoflurane (ISO); 2) to find the adequate durations of thermal support for preventing hypothermia induced by their anesthesia in mice. Adult male ICR mice were anesthetized during 40 min without and with the thermal support for 1 (both anesthetic groups), 2, 3, and 5 hr (in MMB group). Without thermal support, the decrease of body temperature in MMB group were more severe than that in ISO group. The durations of thermal support completely prevented hypothermia at 5 hr-support in MMB group and that at 1 hr-support in ISO group. However, the other short durations did not prevent hypothermia at 1, 2 and 3 hr-support in MMB group. These results suggest that the mice should be received thermal support over 5 hr after injection of MMB anesthesia to prevent hypothermia.