Heating Pad Performance and Efficacy of 2 Durations of Warming after Isoflurane Anesthesia of Sprague-Dawley Rats (

Anesthetic agents depress thermoregulatory mechanisms, causing hypothermia within minutes of induction of general anesthesia. The consequences of hypothermia include delayed recovery and increased experimental variability. Even when normothermia is maintained during anesthesia, hypothermia may occur during recovery. The primary aim of this study was to identify an effective warming period for maintaining normothermia during recovery. Adult male (n = 8) and female (n = 9) Sprague-Dawley rats were randomized to 30 min (post30) or 60 min (post60) of warming after recovery from anesthesia. During a 40-min anesthetic period, normothermia (target, 37.5 ± 1.1 °C) was maintained by manual adjustment of an electric heating pad in response to measured rectal temperatures (corrected to estimate core body temperature). Warming was continued in a recovery cage according to treatment group. Rectal temperature was measured for a total of 120 min after anesthesia. Heating pad performance was assessed by measuring temperatures at various sites over its surface. One female rat in the post30 group was excluded from analysis. Normothermia was effectively maintained during and after anesthesia without significant differences between groups. In the post60 group, core temperature was slightly but significantly increased at 90 and 100 min compared with baseline. One rat in each treatment group became hyperthermic (>38.6 °C) during recovery. During recovery, the cage floor temperature required approximately 30 min to stabilize. The heating pad produced heat unevenly over its surface, and measured temperatures frequently exceeded the programmed temperature. Providing 30 min of warming immediately after anesthesia effectively prevented hypothermia in rats. Shorter warming periods may be useful when recovery cages are preheated.