Influence of acepromazine on the cardiovascular effects of dobutamine in isoflurane-anaesthetised horses premedicated with romifidine.

Objective: To explore the influence of acepromazine on the cardiovascular effects of dobutamine in isoflurane-anaesthetised horses premedicated with romifidine.

Study Design: Prospective randomised clinical trial.

Animals: A total of 18 horses undergoing elective arthroscopy were enrolled, of which 12 horses requiring dobutamine were included.

Methods: Horses were randomised to receive acepromazine 0.02 mg kg (Group A+) intravenously (IV) or none (Group A-), 35 minutes before anaesthesia. Horses received xylazine 0.2 mg kg concurrently to facilitate IV access. Horses were premedicated with romifidine 0.08 mg kg, induced with ketamine 2.2 mg kg and diazepam 0.08 mg kg IV, and maintained with isoflurane in oxygen. Dobutamine infusion was commenced when mean arterial pressure (MAP) was < 60 mmHg. Cardiovascular data were collected prior to dobutamine, and at a target MAP of ≥ 70 mmHg. Dobutamine start time from induction, duration and dose to reach target MAP were compared using Mann-Whitney U test. Cardiovascular variables were compared using repeated measures ANOVA and post-hoc Fisher's least significant difference test.

Results: Cardiac index (CI) and its percentage change from baseline were significantly higher at target MAP in group A+ [62.0 (49.9-74.2) mL minute kg; 42.8 (17.0-68.7) %] than in A- [49.5 (39.6-59.5) mL minute kg; -4.05 (-21.2-13.0) %] (p = 0.049; p = 0.003). Group A+ required significantly earlier dobutamine [20 (18-25) minutes] than group A- [36 (27-60) minutes] (p = 0.02). Group A+ required significantly higher dobutamine dose [1.5 (1-2.5) μg kg minute] to reach target MAP than group A- [0.5 (0.5-1) μg kg minute] (p = 0.009).

Conclusion And Clinical Relevance: Dobutamine significantly increased MAP and CI following pre-anaesthetic acepromazine sedation, in isoflurane-anaesthetised horses premedicated with romifidine. Without acepromazine, dobutamine increased MAP but not CI. Interactions between acepromazine, romifidine and dobutamine on the cardiovascular system should be considered.