Effect of Postoperative Xylazine Administration on Cardiopulmonary Function and Recovery Quality After Isoflurane Anesthesia in Horses

ObjectiveTo evaluate equine cardiopulmonary function and recovery quality after administration of 0.25 or 0.50mg/kg xylazine intravenously (IV) during recovery. Study DesignRandomized, blinded, prospective, clinical study. AnimalsHorses (n=20). MethodsDuring recovery after 3hours of isoflurane anesthesia for arthroscopic surgery, horses were administered either 0.25mg/kg (G25, n=10) or 0.50mg/kg (G50, n=10) xylazine intravenously. Vital signs and arterial blood samples were obtained during recovery before sedation (baseline), 5, 10, 20, 30, and 45minutes after xylazine and 30minutes after standing. The quality of recovery scores ranged from 10 to 72 (10=best, 72=worst). ResultsG25 horses recovered faster (meanSD, 33 +/- 5min) than G50 horses (50 +/- 7min, P<.0001). Mean maximal decrease in arterial oxygen tension was 55 +/- 11mmHg in G25 (at 10minutes; P<.05) and 54 +/- 7mmHg in G50 (at 20minutes; P<.01). G25 group had a total recovery score (23 [range 18-29]) and number of attempts to stand (4 +/- 2) greater than the G50 group (18 [10-23] and 1 +/- 1, respectively; P<.001). ConclusionsBoth doses of xylazine promoted a moderate and transient hypoxemia during recovery; however, the 0.5mg/kg dose produced a longer and improved quality of recovery from anesthesia.