Effects of a constant rate infusion of detomidine on cardiovascular function, isoflurane requirements and recovery quality in horses

Objective To examine the influence of a detomidine constant rate infusion (CRI) on cardiovascular function, isoflurane requirements and recovery quality in horses undergoing elective surgery. Study design Prospective, randomized, blinded, clinical trial. Animals Twenty adult healthy horses. Methods After sedation (detomidine, 10 mu g kg(-1) intravenously [IV]) and induction of anaesthesia (midazolam 0.06 mg kg(-1), ketamine 2.2 mg kg(-1) IV), anaesthesia was maintained with isoflurane in oxygen/air (inspiratory oxygen fraction 55%). When indicated, the lungs were mechanically ventilated. Dobutamine was administered when MAP < 70 mmHg. The horses were randomly allocated to one of two groups and throughout anaesthesia, received either a detomidine (5 mu g kg(-1) hour(-1)) (D) or saline (S) CRI, with the anaesthetist unaware of the treatment. Monitoring included end-tidal isoflurane concentration, arterial pH, PaCO(2), PaO(2), dobutamine administration rate, heart rate (HR), arterial pressure, cardiac index (CI), systemic vascular resistance (SVR), stroke index and oxygen delivery index ((D) over dotO(2)I). For recovery from anaesthesia, all horses received 2.5 mu g kg(-1) detomidine IV. Recovery quality and duration were recorded in each horse. For statistical analysis, ANOVA, Pearson chi-square and Wilcoxon rank sum tests were used as relevant. Results Heart rate (p = 0.0176) and (D) over dotO(2)I (p = 0.0084) were lower and SVR higher (p = 0.0126) in group D, compared to group S. Heart rate (p = 0.0011) and pH (p = 0.0187) increased over time. Significant differences in isoflurane requirements were not detected. Recovery quality and duration were comparable between treatments. Conclusions and clinical relevance A detomidine CRI produced cardiovascular effects typical for alpha(2)-agonists, without affecting isoflurane requirements, recovery duration or recovery quality