Effect of Postoperative Xylazine Administration on Cardiopulmonary Function and Recovery Quality After Isoflurane Anesthesia in Horses Keila K. Ida 1 , DVM, Msc, Denise T. Fantoni 1 , DVM, PhD, Bruna T. Ibiapina 2 , DVM, Maria‐Teresa M. R. Souto 3 , DVM, Msc, André L. V. Zoppa 3 , DVM, PhD, Luis Claudio L. C. Silva 3 , DVM, PhD, and Aline M. Ambrósio 3 , DVM, PhD 1 Laboratório de Investigação Médica LIM‐08, Anestesiologia, Faculdade de Medicina, Universidade de São Paulo (USP), São Paulo, Brazil , 2 Hospital Veterinário, Faculdade de Medicina Veterinária e Zootecnia (FMVZ), USP, São Paulo, Brazil and 3 Departamento de Cirurgia, FMVZ, USP, São Paulo, Brazil Corresponding Author Dr. Keila K. Ida, DVM, Msc, Faculdade de Medicina, Laboratório de Investigação Médica LIM‐08, Anestesiologia, Universidade de São Paulo, Av. Doutor Arnaldo, 455, 2° andar, sala 2120, Cerqueira César, 01246‐903, São Paulo, SP, Brazil. E‐mail: keilaida@usp.br Submitted July 2011 Accepted December 2011 DOI:10.1111/j.1532-950X.2013.12050.x Objective: To evaluate equine cardiopulmonary function and recovery quality after administration of 0.25 or 0.50 mg/kg xylazine intravenously (IV) during recovery. Study Design: Randomized, blinded, prospective, clinical study. Animals: Horses (n ¼ 20). Methods: During recovery after 3 hours of isoflurane anesthesia for arthroscopic surgery, horses were administered either 0.25 mg/kg (G25, n ¼ 10) or 0.50 mg/kg (G50, n ¼ 10) xylazine intravenously. Vital signs and arterial blood samples were obtained during recovery before sedation (baseline), 5, 10, 20, 30, and 45 minutes after xylazine and 30 minutes after standing. The quality of recovery scores ranged from 10 to 72 (10 ¼ best, 72 ¼ worst). Results: G25 horses recovered faster (mean  SD, 33  5 min) than G50 horses (50  7 min, P < .0001). Mean maximal decrease in arterial oxygen tension was 55  11 mmHg in G25 (at 10 minutes; P < .05) and 54  7 mmHg in G50 (at 20 minutes; 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). Conclusions: Both doses of xylazine promoted a moderate and transient hypoxemia during recovery; however, the 0.5 mg/kg dose produced a longer and improved quality of recovery from anesthesia. INTRODUCTION Isoflurane is an inhalant anesthetic with a low blood‐gas solubility coefficient that is often associated with a rapid recovery from nonsurgical procedures in horses. 1 Recovery from surgical procedures is described as ataxic and agitated with multiple attempts to stand. 2–4 A short recovery time from anesthesia in horses is associated with poor recovery quality and numerous attempts to stand, which may increase complications. 1–6 Excitement is a major consideration during recovery from anesthesia in horses. 5 Horses may attempt to stand as consciousness is regained despite inappropriate muscle strength or incoordination. 7 Generally, these early attempts to stand are not successful, and they are associated with complications, including fractures, joint dislocations, lacer- ations and wound dehiscence. 4,8–11 Administration of alpha‐2 agonists during recovery from anesthesia improves recovery quality. 5 The appropriate sedative and analgesic effects reduce anxiety, increase recumbency times, and prevent early attempts to stand. 9 Xylazine is the most commonly used alpha‐2 agonist for this purpose because a low dose induces shorter recoveries and less cardiovascular and respiratory depression than romifidine and detomidine at equipotent doses. 5,12,13 At lower doses, additional sedation may be required because a single low dose may not prevent early attempts to stand. 14 However, the safety of larger doses of xylazine during recovery from isoflurane anesthesia in horses is unknown. Our purpose was to evaluate recovery quality and cardiopulmo- nary function after administration of 0.25 and 0.50 mg/kg xylazine during recovery from isoflurane anesthesia in horses. MATERIALS AND METHODS Horses The Bioethical Committee (Protocol number 1774/09) approved this study. After obtaining client consent, mixed‐ Presented in part as an abstract at the 9th Brazilian Meeting of Veterinary Anesthesiology, Goiânia, Brazil, November 4–6, 2009. Veterinary Surgery 9999 (2013) 1–8 © Copyright 2013 by The American College of Veterinary Surgeons 1