Anesthesia of North American River Otters (Lutra canadensis) with Medetomidine-Ketamine and Reversal by Atipamezole

North American river otters (Lutra canadensis) were anesthetized in cooperation with an otter restoration program administered by the North Carolina Wildlife Resources Commission during winter 1993. Five doses of medetomidine (10, 25, 50, 75, and 100 μg/kg, i.m.) in combination with ketamine (2.5 mg/kg, i.m.) were evaluated in 41 river otters. Heart rate and rhythm, respiratory rate, rectal temperature, relative oxyhemoglobin saturation, systolic, diastolic, and mean arterial blood pressures were monitored at 5-min intervals for 30 min. Otters were anesthetized at all but the lowest dose (medetomidine 10 μg/kg--ketamine 2.5 mg/kg), which produced heavy sedation of short duration. We recommend medetomidine 25 μg/kg combined with ketamine 2.5 mg/kg, i.m., in river otters for anesthetic induction prior to inhalation anesthesia or for short procedures, including minor surgery. A higher dose of medetomidine (50 μg/kg) in combination with ketamine (2.5 mg/kg) is required for procedures of 25 min or longer, but respiratory depression may occur. Atipamezole (50-200 μg/kg, i.m.) reversed the effects of medetomidine--ketamine in otters. Total recovery time was shorter with higher doses of atipamezole relative to the medetomidine dose, and a ratio of 4:1 (atipamezole: medetomidine) worked best in these trials.