Use of Ketamine or Xylazine to Provide Balanced Anesthesia with Isoflurane in C57BL/6J Mice
Balanced anesthesia—the use of a combination of drugs to achieve a desired anesthetic plane—offers many benefits, including smoother induction and recovery and fewer adverse effects than occur with individual drugs. Although premedication prior to inhalant anesthesia is
routine in other species, mice are commonly induced with gas anesthesia alone. The hypothesis of this study was that premedication with ketamine or xylazine would safely reduce the stress of isoflurane induction and lower the minimum alveolar concentration (MAC) of isoflurane. Young adult
male and female C57BL/6J mice were premedicated with ketamine (100 mg/kg), xylazine (4 mg/kg), or isotonic crystalloid (0.1 mL) and were used in 4 experiments. First, isoflurane induction was video recorded under all test conditions, and the videos were scored according to a behavioral ethogram
to identify signs of distress. Mice in the ketamine group experienced tremors and ataxia before and dur- ing induction. Therefore, ketamine was given after induction with isoflurane in subsequent experiments. Second, the MAC value for each anesthetic protocol was determined by using quantal
and bracketing analysis. Third, mice were anesthetized according to the 3 protocols, and vital parameters were monitored for 60 min. Finally, anesthetized mice were challenged with hypoxia and hypovolemia, and vital parameters were monitored. Premedication with xylazine significantly reduced
the stress scores for isoflurane induction (control, 7.3 ± 1.5; ketamine, 6.0 ± 3.0; xylazine, 3.1 ± 1.0). Ketamine and xylazine both reduced the MAC of isoflurane (control, 1.89%; ketamine, 0.96%; xylazine, 1.20%). All mice survived 60 min of anesthesia and the hypoxia-hypovolemia
challenge. Premedication with xylazine reduced the stress of induction and lowered the necessary dose of isoflurane in C57BL/6J mice to maintain a surgical plane of anesthesia. We recommend administering xylazine before isoflurane induction and anesthesia of healthy mice that are undergoing
procedures in which 100% oxygen is provided and anticipated blood loss is less than 10% to 15% of the total blood volume.