Clinical effects of two doses of butorphanol with detomidine for intravenous premedication of healthy warmblood horses

Abstract

Objective: To compare the effects of two different doses of butorphanol combined with detomidine administered intravenously (IV) on quality of sedation, degree of ataxia and anaesthetic induction in horses.

Study design: Randomized, blinded, clinical study.

Animals: A total of 40 client-owned healthy warmblood horses scheduled for elective surgery under general anaesthesia.

Methods: Horses were randomly allocated to be administered 8 μg kg^-1 detomidine IV plus either 20 or 50 μg kg^-1 butorphanol IV, with the principal investigator blinded to group allocation. Head height was measured before drug injection and 2 minutes thereafter. Data were compared using unpaired t test. Horses were filmed and scored using Simple Descriptive Scales for sedation (2 and 15 minutes after IV injection), ataxia (at walk, immediately after the 2 minute time point) and quality of swing-door induction following diazepam and ketamine administration. Data are shown as median (and range where appropriate). Scores were compared using chi-square tests (p < 0.05).

Results: There were 14 and 17 horses in high-dose (HD) and low-dose (LD) groups respectively. Data from nine horses were excluded. Mean head height reduction did not differ between groups (p = 0.86), nor did sedation scores at 2 minutes (median = 3 in both groups; p = 0.09) or 15 minutes (median = 2 in both groups; p = 0.63). There was no significant difference in the requirement for additional detomidine (p = 0.73) or in induction quality between groups (p = 0.99), but initial ataxia was significantly greater in the HD group 2 (1-3) versus 2.5 (1-3) in the LD group (p = 0.017).

Conclusions and clinical relevance: In healthy warmblood horses, simultaneous administration of 50 rather than 20 μg kg^-1 butorphanol with 8 μg kg^-1 detomidine does not provide greater sedation or affect induction, but it causes more pronounced ataxia shortly after IV injection.

Keywords: ataxia; butorphanol; detomidine; premedication; sedation.