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GENERAL anaesthesia presents a particularly high mortality and morbidity risk in horses (Johnston and others 2002). Several sedative protocols have been proposed for standing surgery in horses, all involving α2-adrenoreceptor agonists with or without opioids (Bettschart-Wolfensberger and others 1999, Sellon and others 2001, 2004).
Opioids (μ or κ agonists) act synergistically to α2-adrenoceptor agonists and improve analgesia and balance sedation. By reducing the required dose of α2-adrenoceptor agonists, deleterious cardiopulmonary side effects can be reduced (England and Clark 1996). Butorphanol has been used as a constant rate infusion (CRI) and its efficacy has been proven in combination with xylazine or as a sole agent in horses (Robertson and Muir 1983, Sellon and others 2001). Ketamine has analgesic properties in horses when administered at subanaesthetic doses (Fielding and others 2006, Lankveld and others 2006, Peterbauer and others 2008) but it does not provide sedation at plasma concentrations that result in an analgesic effect (Lankveld and others 2006). In horses, xylazine is the shortest-acting α2-adrenoceptor agonist and its cardiovascular side effects are also of shorter duration (England and others 1992).
The purpose of this study was to compare the dose of xylazine necessary to maintain sufficient sedation and analgesia to perform common carotid translocation in standing horses and to compare the influence of butorphanol CRI with morphine-ketamine CRI on the rate of infusion of xylazine.
Eight horses classified …