Evaluation of cardiovascular, respiratory and biochemical effects, and anesthetic induction and recovery behavior in horses anesthetized with a 5% micellar microemulsion propofol formulation

Objective: To characterize cardiovascular, respiratory and biochemical effects and recovery behavior associated with a 3-hour continuous infusion of a micellar microemulsion propofol formulation in horses. Study design: Prospective experimental trial. Animals: Six healthy adult horses, 9 ± 2 years old and weighing 557 ± 14 kg. Methods: All horses received xylazine (1 mg kg^-1, IV) 5 minutes prior to anesthetic induction. Each horse was anesthetized on two occasions with a 5% micellar microemulsion propofol formulation (2 mg kg^-1, IV); first as a single bolus (phase I) and then as a 3-hour continuous infusion (phase II). Propofol pharmacokinetics were obtained from phase I and used to determine the starting infusion rates in phase II. Anesthetic induction and recovery characteristics were quantitatively and qualitatively assessed. Cardiovascular, respiratory and biochemical parameters were monitored during anesthesia and recovery. Results: Induction quality varied, ranging from good to poor. Standing and overall recovery quality scores were consistently excellent in phase I but more variability was observed among horses in phase II. Heart rate (HR) and mean arterial pressure (MAP) were adequately maintained but marked hypoventilation developed. There were only minimal changes in blood biochemical analytes following anesthesia. Conclusions and clinical relevance: The micellar microemulsion propofol formulation, administered as a 3-hour continuous infusion, showed similar results compared to those previously described with a commercially available propofol preparation. However, based on present findings, use of propofol as a primary anesthetic in horses for prolonged periods of anesthesia requires further study to determine the limits of safety and clinical applicability.