Assessment of unassisted recovery from repeated general isoflurane anesthesia in horses following post-anesthetic administration of xylazine or acepromazine or a combination of xylazine and ketamine.

Objectives: To compare the effects of sedative doses of acepromazine, xylazine or xylazine/ketamine administered to horses after isoflurane anesthesia on the quality of recovery and anesthesia recovery times. To determine if recovery scores improve after repeated consecutive anesthetic episodes.

Study Design: Prospective, randomized, crossover study.

Animals: Fifteen adult research horses, 6.5±3.4 years old and weighing 499±40 kg.

Methods: Horses undergoing three anesthetic episodes with isoflurane for magnetic resonance of the forelimbs were administered acepromazine (0.02 mg kg(-1) i.v.) or xylazine (0.3 mg kg(-1) i.v.) or xylazine (0.15 mg kg(-1) i.v.) combined with ketamine (0.3 mg kg(-1) i.v.) in random order upon arrival in recovery. The quality of recovery was compared between the three treatments using a composite numerical rating and a general descriptive scoring system.

Results: Horses administered xylazine had better recovery scores than horses administered xylazine/ketamine, associated with better scores during their move to sternal, strength and number of attempts to standing. Horses administered acepromazine had similar recovery scores to horses administered xylazine and to horses administered xylazine/ketamine. Time to sternal recumbency and time to extubation were statistically longer for the xylazine treatment. Time to standing was similar between treatments. Horses had better recovery scores during the third anesthetic episode, regardless of the sedative drug administered, associated with better scores for strength and number of attempts to standing.

Conclusions: Xylazine administration was superior to xylazine/ketamine but similar to acepromazine. This study also indicates that horses improve the quality of recovery during consecutive anesthetics associated with longer time to sternal and to standing, regardless of the sedative used.

Clinical Relevance: All treatments provided good quality recoveries. The experience of the individual horse gained during recent previous anesthetic episodes may have a positive effect in facilitating a better recovery.