Comparison of thermoregulatory devices during rodent anesthesia and the effects of body temperature on physiologic parameters

General anesthesia is a complex physiologic process affecting several body systems, including thermoregulation. Decreased body temperature during anesthesia can affect heart and respiratory rates, blood pressure, cardiac output, and depth of anesthesia, along with adverse effects on the immune system. Thermoregulatory support devices have been proposed to prevent the decrease of body temperature in anesthetized rodents. We tested 2 novel devices, thermogenic gel packs and reflective foils, to compare their effectiveness in maintaining temperatures, as compared with a standard circulating warm water blanket (CCWB) in female C57BL/6 mice. We hypothesized that these novel devices would maintain temperature and limit changes in physiologic parameters. Mice were randomly assigned to experimental groups (n = 7 groups, mice per group): control (no thermal support), reflective foil, gel pack, gel pack and reflective foil, CWWB medium setting, CWWB high setting, CWWB high setting plus reflective foil. Mice were anesthetized for 30 min with 2% isoflurane and provided with warming devices. Body temperature was monitored via rectal probe and subcutaneous transponder every 5 min during anesthesia. Heart rates were recorded with ECG and respiratory rates were assessed visually. Time to regain consciousness after discontinuation of isoflurane also was recorded. Results showed that reflective foil alone was not significantly different than the control group (start temp: 36.2 ± 0.38 °C, end temp: 28.8 ± 0.78 °C) but inclusion of the foil increased the thermogenic properties when combined with other devices. Gel packs and the CWWB on high setting (start temp: 36.0 ± 0.4 °C, end temp: 38.2 ± 0.7 °C) caused a significant increase (P < 0.0001) in body temperatures of mice, whereas the CWWB on the medium setting maintained the body temperature within 1° of 36.1 °C over the 30-min anesthetic time course. We also found a strong, positive correlation between body temperature, physiologic parameters, and recovery times (heart rate compared with body temp: r = 0.94). This information will provide the research community with guidance in the use of thermoregulatory devices for rodents and demonstrates the impact of body temperature during anesthesia on physiologic parameters.