Effect of Methadone Combined With Acepromazine or Detomidine on Sedation and Dissociative Anesthesia in Healthy Horses

Abstract

The aim of this study was to compare the effects of methadone combined with detomidine or acepromazine on the quality of sedation and its influence over dissociative anesthesia in healthy horses. In a crossover design, seven horses were administered with 0.1 mg/kg methadone and 0.02 mg/kg detomidine intravenously (group MD) or 0.1 mg/kg methadone and 0.05 mg/kg acepromazine intravenously (group MA). Subsequently, anesthesia was induced with a combination of 2.2 mg/kg ketamine and 0.1 mg/kg midazolam intravenously. Descriptive scales and footages were used to evaluate the quality of sedation, induction, anesthesia maintenance, and recovery. Physiological parameters, arterial blood gas, and electrolytes were assessed from baseline to the recovery of anesthesia. The MA group showed lower arterial blood pressure and higher heart rate compared with the group MD. A slight decrease in arterial blood oxygen levels was observed after recumbency, more prominently in the MA group. There was no difference in the quality or time of induction or maintenance or recovery of anesthesia between groups. The results suggest that both premedication protocols produce good sedation and quality of anesthesia. Methadone combined with detomidine produced a good cardiopulmonary stability compared with methadone combined with acepromazine and might be safer to be used as premedication for dissociative anesthesia compared with methadone combined with acepromazine in healthy horses.

Keywords: Horse; Ketamine; Midazolam; Neuroleptoanalgesia; Opioid; Sedation.