Hemodynamic influence of acepromazine or dexmedetomidine premedication in isoflurane-anesthetized dogs

OBJECTIVE: To investigate hemodynamic effects of acepromazine and dexmedetomidine premedication in dogs undergoing general anesthesia induced with propofol and maintained with isoflurane in oxygen and assess the influence of these drugs on oxygen-carrying capacity and PCV. DESIGN: Prospective, randomized crossover study. ANIMALS: 6 healthy adult dogs. PROCEDURES: Dogs received acepromazine (0.05 mg/kg [0.023 mg/lb]) or dexmedetomidine (15.0 μg/kg [6.82 μg/lb]) IM. Fifteen minutes later, anesthesia was induced with propofol and maintained at end-tidal isoflurane concentration of 1.28% (1 minimum alveolar concentration) for 30 minutes. Hemodynamic variables were recorded at predetermined times. The experiment was repeated 48 hours later with the alternate premedication. Results were analyzed by repeated-measures ANOVA with a mixed-models procedure. RESULTS: Bradycardia, hypertension, and significant cardiac output (CO) reduction developed after dexmedetomidine premedication but improved during isoflurane anesthesia. Hypotension developed after acepromazine administration and persisted throughout the isoflurane maintenance period, but CO was maintained throughout the anesthetic period when dogs received this treatment. Oxygen delivery and consumption were not different between treatments at most time points, whereas arterial oxygen content was lower with acepromazine premedication owing to lower PCV during isoflurane anesthesia. CONCLUSIONS AND CLINICAL RELEVANCE: Acepromazine exacerbated hypotension, but CO did not change in dogs anesthetized with propofol and isoflurane. Dexmedetomidine reduced CO but prevented propofol-isoflurane-induced hypotension. In general, oxygen-carrying capacity and PCV were higher in dexmedetomidine-treated than in acepromazine-treated dogs anesthetized with propofol and isoflurane.