EFFECT OF LOW-DOSE ATROPINE ADMINISTRATION ON DOBUTAMINE DOSE REQUIREMENT IN HORSES ANESTHETIZED WITH DETOMIDINE AND HALOTHANE

Objective-To determine whether a low dose of atropine is associated wi th decreased requirement for cardiovascular supportive treatment in ho rses given detomidine prior to maintenance of general anesthesia with halothane. Animals-a groups of 10 healthy horses, Procedure-Detomidine (20 mu g/kg of body weight, IM) was administered to ail 30 horses. Th en, 10 horses received atropine (0.006 mg/kg, IV) ? hour after detomid ine administration, 10 horses received atropine (0.012 mg/kg, IM) al t he rime of detomidine administration, and 10 horses served as a contro l group. Heart rate was measured prior to detomidine administration an d at fixed intervals throughout anesthesia. The dobutamine infusion ra te necessary to maintain mean arterial blood pressure between 70 and 8 0 mm of Hg was recorded. Systemic blood pressures, end-tidal halothane , end-tidal CO2, and arterial blood gas tensions were measured at fixe d intervals, Results-Mean heart rate was higher among horses receiving atropine IV or IM, compared with that in control horses. Horses that received atropine IV had higher systemic arterial blood pressure and r equired a lower dobutamine infusion rate than did horses of the other groups. Conclusion-Detomidine-treated, halothane-anesthetized horses g iven atropine IV required less dobutamine, compared with horses receiv ing or not receiving atropine IM. Complications, such as colic and dys rhythmias, from use of higher doses of atropine, were not observed at this lower dose of atropine. Clinical Relevance-IV administration of a low dose of atropine prior to induction of general anesthesia may res ult in improved blood pressure in horses ?hat have received detomidine before anesthesia with halothane.