Comparison of the effects of xylazine bolus versus medetomidine constant rate infusion in horses anesthetised with isoflurane

Inhalant anesthesia in horses carries a high rate of complications and mortality, despite its common use (1-4).

Medetomidine, a selective alpha2 agonist, is approved in North America for use in dogs only (5). However, it is often used in horses as part of a balanced anesthetic protocol by using a constant rate infusion (CRI) of medetomidine and a reduced concentration of isoflurane (6). The premise behind this technique is that the lower concentration of isoflurane may result in less cardiovascular depression, while the addition of medetomidine provides supplemental analgesia and muscle relaxation, and smoothes recoveries (6, 7). Although a medetomidine CRI during isoflurane anesthesia has been evaluated in horses, no studies exist which compare a CRI of medetomidine to conventional xylazine bolus therapy using the same group of horses, breathing spontaneously in dorsal recumbency, without the influence of surgery.

This thesis has three principle sections. The first presents background information and a literature review relevant to the study as a whole. The second section describes the cardiopulmonary and anesthetic effects of medetomidine CRI compared to conventional therapy with xylazine. Finally, the third section describes the stress responses and recovery characteristics of medetomidine CRI compared to conventional therapy with xylazine.