Project description:Carbon dioxide and isoflurane are widely used for killing rats, yet may not truly achieve "euthanasia", because they elicit aversion. The inhalant anesthetic desflurane is faster acting than isoflurane, representing a potential refinement. Using an aversion-avoidance paradigm, 24 rats were exposed to isoflurane or desflurane (n = 12 per group) at initial exposure. Fourteen rats were then re-exposed to isoflurane or desflurane (n = 7 per group), after a 7 days washout period. Initial exposure: time to recumbency was faster for desflurane than isoflurane (p = 0.0008, 95% CI [-12.9 to 32.6 s]), with 9/12 and 6/12 rats becoming recumbent, respectively. At initial exposure, there was no difference between groups in time to withdrawal (p = 0.714). At re-exposure, all rats withdrew and no rats became recumbent. Time to withdrawal at re-exposure did not differ between treatment groups (p = 0.083). Compared to initial exposure, time to withdrawal during re-exposure was similar for isoflurane (p = 0.228) and faster with desflurane (p = 0.012, 95% CI [19.1 to 49.5 s]). Isoflurane and desflurane are similarly aversive, with aversion increasing at re-exposure. The shorter time from exposure to recumbency with desflurane indicates that any distress is of a shorter duration when compared with isoflurane.
Project description:In humans and other mammals, general anesthesia impairs thermoregulation, leading to warm core blood redistributing to the periphery. This redistribution is an important contributor to hypothermia that can be reduced with pre-warming before anesthesia. Additionally, sedation following premedication has been associated with hypothermia in dogs. In a prospective, randomized, cross-over study, 8 adult male and female rats (weighing 388 to 755 g) were sedated with intramuscular ketamine-midazolam-hydromorphone, then placed in an unwarmed cage or warmed box for 14 minutes, followed by 30 minutes of isoflurane anesthesia with active warming. Core body temperature was monitored throughout. After sedation, warmed rats gained 0.28°C ± 0.13°C and unwarmed rats lost 0.19°C ± 0.43°C, a significant difference between groups (P = 0.004). After anesthesia, warmed rats maintained higher core temperatures (P < 0.0001) with 2/8 and 6/8 of warmed and unwarmed rats becoming hypothermic, respectively. Pre-warming during sedation and active warming during general anesthesia is effective in minimizing hypothermia.
Project description: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.