Influence of a constant rate infusion of dexmedetomidine on cardiopulmonary function and recovery quality in isoflurane anaesthetized horses

Objective To investigate the influence of a dexmedetomidine constant rate infusion (CRI) in horses anaesthetized with isoflurane. Study design Prospective, randomized, blinded, clinical study. Animals Forty adult healthy horses (weight mean 491 +/- SD 102 kg) undergoing elective surgery. Methods After sedation [dexmedetomidine, 3.5 mu g kg(-1) intravenously (IV)] and induction IV (midazolam 0.06 mg kg(-1), ketamine 2.2 mg kg(-1)), anaesthesia was maintained with isoflurane in oxygen/air (FiO(2) 55-60%). Horses were ventilated and dobutamine was administered when hypoventilation [arterial partial pressure of CO(2) > 8.00 kPa (60 mmHg)] and hypotension [arterial pressure 70 mmHg] occurred respectively. During anaesthesia, horses were randomly allocated to receive a CRI of dexmedetomidine (1.75 mu g kg(-1) hour(-1)) (D) or saline (S). Monitoring included end-tidal isoflurane concentration, cardiopulmonary parameters, and need for dobutamine and additional ketamine. All horses received 0.875 mu g kg(-1) dexmedetomidine IV for the recovery period. Age and weight of the horses, duration of anaesthesia, additional ketamine and dobutamine, cardiopulmonary data (ANOVA), recovery scores (Wilcoxon Rank Sum Test), duration of recovery (t-test) and attempts to stand (Mann-Whitney test) were compared between groups. Significance was set at p < 0.05. Results Heart rate and arterial partial pressure of oxygen were significantly lower in group D compared to group S. An interaction between treatment and time was present for cardiac index, oxygen delivery index and systemic vascular resistance. End-tidal isoflurane concentration and heart rate significantly increased over time. Packed cell volume, systolic, diastolic and mean arterial pressure, arterial oxygen content, stroke volume index and systemic vascular resistance significantly decreased over time. Recovery scores were significantly better in group D, with fewer attempts to stand and significantly longer times to sternal position and first attempt to stand. Conclusions and clinical relevance A dexmedetomidine CRI produced limited cardiopulmonary effects, but significantly improved recovery quality