Comparison of three α2-antagonists, yohimbine, tolazoline, or atipamezole for reversing the anesthetic effects of medetomidine and ketamine in dairy calves

Abstract

Yohimbine (0.25 mg/kg i.v.), tolazoline (2.2 μg/kg i.v.) or atipamezole (60 μg/kg i.v.) were given to 6 healthy, Holstein calves (156.8-241.1 kg) 30 min after anaesthesia with a combination (MK) of medetomidine (20 μg/kg i.v.) and ketamine (2.2 mg/kg i.v.) with an interval of 1 week between treatments. Heart and respiratory rates, indirect arterial blood pressures (systolic (SAP), mean (MAP), diastolic (DAP)), and arterial blood gases were measured. Calves became sternally recumbent in 2±14 s for a duration of 94±25 min after administration of MK. Respiratory rate, PaCO2 and arterial blood pressure were significantly increased while PaO2, pHa and SaO2 were significantly decreased during anaesthesia. The values for most of the blood gas variables returned to normal after administration of tolazoline and atipamezole. The duration of recumbency following administration of yohimbine, tolazoline, or atipamezole was 80±22, 46±9 and 34±3 min, respectively. Calves stood in 48±20, 16±9 and 4±3 min, respectively, after the injection of yohimbine, tolazoline and atipamezole. It was concluded that medetomidine and ketamine combination can be used effectively to induce anaesthesia in dairy calves. Either tolazoline or atipamezole can be administered to antagonize the anaesthetic effects and induce rapid recovery.