Comparison of 6 Injectable Anesthetic Regimens and Isoflurane in Gray Short-tailed Opossums (Monodelphis domestica).

Gray short-tailed opossums are used in a wide variety of research in the areas of developmental biology, oncology, immunology, and comparative biology. Despite many frequent experimental manipulations of these animals under anesthesia, few studies to date have characterized the effects of anesthesia in this species. Our aim was to identify safe and effective injectable anesthetic combinations using ketamine and xylazine or ketamine and dexmedetomidine at doses of 40 mg/kg to 100 mg/kg for ketamine, 5 mg/kg to 10 mg/kg for xylazine, and 0.05 mg/kg to 0.1 mg/kg for dexmedetomidine. Effects of the proposed regimens ranged from light sedation to surgical anesthesia, but only 100 mg/kg ketamine + 0.1 mg/kg dexmedetomidine induced surgical anesthesia in all opossums, with a mean duration of 25.4 min. The 2 lowest doses of ketamine and xylazine (40 mg/kg ketamine + 5 mg/kg xylazine and 40 mg/kg ketamine + 10 mg/kg xylazine) achieved sedation to light anesthesia in all animals but did not produce a surgical plane of anesthesia in any animal. All regimens that induced a surgical plane of anesthesia caused bradycardia and bradypnea, and 75 mg/kg ketamine + 10 mg/kg xylazine and 100 mg/kg ketamine + 0.1 mg/kg dexmedetomidine caused the greatest decreases in SpO2. Except for one opossum that died of unknown causes, all animals remained healthy and apparently free of anesthetic complications. Among all treatments, isoflurane delivered by a precision vaporizer provided the most consistent and reliable anesthesia; therefore, we recommend inhalant anesthesia over the injectable combinations used in this study.