Hemodynamic effects of incremental doses of acepromazine in isoflurane-anesthetized dogs

Abstract

Objective: To evaluate the effects of incremental doses of acepromazine on hemodynamics in isoflurane-anesthetized dogs.

Study design: Prospective, experimental study.

Animals: Healthy, adult, mixed-breed dogs (two male and four female) weighing 16.8 ± 5.1 kg (mean ± standard deviation).

Methods: Dogs were anesthetized with propofol (7 mg kg^-1) intravenously (IV) and isoflurane. Thermodilution and arterial catheters were placed for hemodynamic monitoring and arterial blood sampling for blood gas analysis. Baseline measurements were performed with stable expired concentration of isoflurane (Fe'Iso) at 1.8%. Each dog was then administered four incremental acepromazine injections (10, 15, 25 and 50 μg kg^-1) IV, and measurements were repeated 20 minutes after each acepromazine injection with Fe'Iso decreased to 1.2%. The four acepromazine injections resulted in cumulative doses of 10, 25, 50 and 100 μg kg^-1 (time points ACP₁₀, ACP₂₅, ACP₅₀ and ACP₁₀₀, respectively).

Results: Compared with baseline, cardiac index (CI) increased significantly by 34%, whereas systemic vascular resistance index (SVRI) decreased by 25% at ACP₅₀ and ACP₁₀₀. Arterial oxygen content (CaO₂) was significantly lower than baseline after all acepromazine injections (maximum decreases of 11%) and was lower at ACP₅₀ and ACP₁₀₀ than at ACP₁₀. No significant change was found in heart rate, stroke index, oxygen delivery index and systolic, mean and diastolic blood pressures. Hypotension (mean arterial pressure < 60 mmHg) was observed in one dog at baseline, ACP₁₀, ACP₂₅ and ACP₁₀₀, and in two dogs at ACP₅₀.

Conclusions and clinical relevance: Compared with isoflurane alone, anesthesia with acepromazine-isoflurane resulted in increased CI and decreased SVRI and CaO₂ values. These effects were dose-related, being more pronounced at ACP₅₀ and ACP₁₀₀. Under the conditions of this study, acepromazine administration did not change blood pressure.

Keywords: canine; cardiovascular; inhalation anesthesia; neuroleptics; phenothiazine derivatives.