Pre-warming following premedication limits hypothermia before and during anesthesia in Sprague-Dawley rats (Rattus norvegicus).

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.