Effects of xylazine hydrochloride during isoflurane-induced anesthesia in horses

Objective-To quantitate dose- and time-related anesthetic-sparing effects o f xylazine hydrochloride (XYL) during isoflurane-induced anesthesia in hors es and to characterize selected physiologic responses of anesthetized horse s to administration of XYL. Animals-6 healthy adult horses. Procedure-Horses were anesthetized 2 times to determine the minimum alveola r concentration (MAC) of isoflurane in O-2 and to characterize the anesthet ic-sparing 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 measur ed 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 administrat ion 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 litt le among treatments. Administration of XYL increased blood glucose concentr ation; the magnitude of change was dose- and time-dependent. Urine volume i ncreased but not significantly. Conclusions and Clinical Relevance-Administration of XYL reduced the anesth etic requirement for isoflurane in horses. The magnitude of the decrease is dose- and time-dependent. Administration of XYL increases blood glucose co ncentration in anesthetized horses in a dose-related manner.