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A comparison of equine recovery characteristics after isoflurane or isoflurane followed by a xylazine-ketamine infusion

Wagner, Ann E., Mama, Khursheed R., Steffey, Eugene P., Hellyer, Peter W.
Veterinary anaesthesia and analgesia 2008 v.35 no.2 pp. 154-160
isoflurane, ketamine, xylazine, horses, anesthesia, veterinary drugs, general anesthetics, drug evaluation, combination drug therapy, drug synergism, dosage, intranasal administration, pharmacokinetics, hemodynamics, breathing, dose response, anesthesia reversal
To determine whether infusion of xylazine (XYL) and ketamine (KET) for 30 minutes after isoflurane administration in horses would result in improved quality of recovery from anesthesia, without detrimental cardiopulmonary changes. Randomized, blinded experimental trial. Seven healthy adult horses aged 6.4 ± 1.9 years and weighing 506 ± 30 kg. Horses were anesthetized twice, at least 1 week apart. On both occasions, anesthesia was induced by the administration of XYL, diazepam, and KET, and maintained with isoflurane for approximately 90 minutes, the last 60 minutes of which were under steady-state conditions (1.2 times the minimum alveolar concentration isoflurane). On one occasion, horses were allowed to recover from isoflurane anesthesia, while on the other, XYL and KET were infused for 30 minutes after termination of isoflurane administration. Heart rate, respiratory rate, arterial blood pressure, pH, and blood-gases were measured and recorded at set intervals during steady-state isoflurane anesthesia and XYL-KET infusion. Recovery events were timed and subjectively scored by one nonblinded and two blinded observers. Data were analyzed using a restricted maximum likelihood-based mixed effect model repeated measures analysis. Infusion of XYL and KET resulted in longer recovery times, but there was no significant improvement in recovery quality score. Under the conditions of this study, infusion of XYL and KET does not positively influence recovery from isoflurane anesthesia in horses. This study does not support the routine use of XYL and KET infusions in horses during the transition from isoflurane anesthesia to recovery.