Sources of Variability in Recovery Time from Methohexital Sodium Anesthesia in Snakes

Variability in anesthetic effect is frequently observed in individuals within a species, yet few studies have investigated its causes in reptiles. To evaluate potential sources of variability in reptile anesthesia, we conducted experiments to test for effects of body temperature, body condition, gravidity, and time post-feeding on the recovery time of Red-sided Garter Snakes (Thamnophis sirtalis parietals) anesthetized with methohexital sodium (Brevital Sodium). The mean recovery time of snakes anesthetized at 21 degrees C was 125 min, at 26 degrees C it was 86 min, and at 31 degrees C it was 64 min. There was a significant correlation between body condition and recovery time, with thinner snakes experiencing longer recovery times. Gravid snakes anesthetized within five weeks of parturition had a mean recovery time that was twice as long as nongravid snakes of a similar mass. Time post-feeding did not have a statistically significant effect on the recovery time in snakes that were anesthetized one, three, and ten days after consuming 30% of their body mass in food. Based on our findings, we provide recommendations for producing more predictable results when using methohexital sodium in reptiles.