Objective: To evaluate the effects of a constant rate infusion (CRI) of romifidine on the requirement of isoflurane, cardiovascular performance and recovery in anaesthetized horses undergoing arthroscopic surgery.
Study design: Randomized blinded prospective clinical trial.
Animals: Thirty horses scheduled for routine arthroscopy.
Methods: After premedication (acepromazine 0.02 mg kg(-1), romifidine 80 microg kg(-1), methadone 0.1 mg kg(-1)) and induction (midazolam 0.06 mg kg(-1) ketamine 2.2 mg kg(-1)), anaesthesia was maintained with isoflurane in oxygen. Horses were assigned randomly to receive a CRI of saline (group S) or 40 microg kg(-1) hour(-1) romifidine (group R). The influences of time and treatment on anaesthetic and cardiovascular parameters were evaluated using an analysis of variance. Body weight (t-test), duration of anaesthesia (t-test) and recovery score (Wilcoxon Rank Sum Test) were compared between groups. Significance was set at p < 0.05.
Results: All but one horse were positioned in the dorsal recumbent position and ventilated from the start of anaesthesia. End tidal isoflurane concentrations were similar in both groups at similar time points and over the whole anaesthetic period. Cardiac output was significantly lower in horses of the R group, but there were no significant differences between groups in cardiac index, body weight or age. All other cardiovascular parameters were similar in both groups. Quality of recovery did not differ significantly between groups, but more horses in group R stood without ataxia at the first attempt. One horse from group S had a problematic recovery.
Conclusions and clinical relevance: No inhalation anaesthetic sparing effect or side effects were observed by using a 40 microg kg(-1) hour(-1) romifidine CRI in isoflurane anaesthetized horses under clinical conditions. Cardiovascular performance remained acceptable. Further studies are needed to identify the effective dose of romifidine that will induce an inhalation anaesthetic sparing effect in anaesthetized horses.