Optimization of intraperitoneal injection anesthesia in mice: drugs, dosages, adverse effects, and anesthesia depth.

PURPOSE: The goals of the study were to find a safe intraperitoneal injection anesthesia protocol for medium-duration surgery in mice (e.g., embryo transfer/vasectomy) coupled with a simple method to assess anesthesia depth under routine laboratory conditions. METHODS: Eight anesthetic protocols consisting of combinations of dissociative anesthetics (ketamine, tiletamine), alpha2-agonists (xylazine, medetomidine), and/or sedatives (acepromazine, azaperone, zolazepam) were compared for their safety and efficacy (death rate, surgical tolerance), using observations and reflex tests. The four best protocols were further evaluated during vasectomy: physiologic measurements (respiratory rate, electrocardiogram, arterial blood pressure, body temperature, blood gas tensions, and acid-base balance) were used to characterize the quality of anesthesia. The reactions of physiologic parameters to surgical stimuli were used to determine anesthesia depth, and were correlated with reflex test results. RESULTS: The protocol with the highest safety margin and the longest time of surgical tolerance (54 min) was ketamine/ xylazine/acepromazine. Three further anesthetic combinations were associated with surgical tolerance: ketamine/ xylazine, ketamine/xylazinelazaperone, and tiletamine/xylazine/zolazepam (Telazol/xylazine). The protocols consisting of ketamine/medetomidine and ketamine/azaperone were not associated with clearly detectable surgical tolerance. The most reliable parameter of surgical tolerance under routine laboratory conditions was the pedal withdrawal reflex. CONCLUSIONS: The best intraperitoneal injection anesthesia regimen consisted of ketamine/xylazine/acepromazine. The dose must be adapted to the particulars of each experimental design (mouse strain, sex, age, mutation). This is best done by measuring surgical tolerance, using the pedal withdrawal reflex.