Objective—To quantitate dose- and time-related
anesthetic-sparing effects of xylazine hydrochloride
(XYL) during isoflurane-induced anesthesia in horses
and to characterize selected physiologic responses of
anesthetized horses to administration of XYL.
Animals—6 healthy adult horses.
Procedure—Horses were anesthetized 2 times to
determine the minimum alveolar concentration (MAC)
of isoflurane in O2 and to characterize the anestheticsparing
effect (MAC reduction) after IV administration
of XYL (0.5 and 1 mg/kg of body weight, random
order). Selected measures of cardiopulmonary function,
blood glucose concentrations, and urinary output
also were measured during the anesthetic studies.
Results—Isoflurane MAC (mean ± SEM) was
reduced by 24.8 ± 0.5 and 34.2 ± 1.9% at 42 ± 7 and
67 ± 10 minutes, respectively, after administration of
XYL at 0.5 and 1 mg/kg. Amount of MAC reduction by
XYL was dose- and time-dependent. Overall, cardiovascular
and respiratory values varied little among
treatments. Administration of XYL increased blood
glucose concentration; the magnitude of change was
dose- and time-dependent. Urine volume increased
but not significantly.
Conclusions and Clinical Relevance—Administration
of XYL reduced the anesthetic requirement
for isoflurane in horses. The magnitude of the
decrease is dose- and time-dependent. Administration
of XYL increases blood glucose concentration
in anesthetized horses in a dose-related manner.
(Am J Vet Res 2000;61:1225–1231)