Hemodynamic, respiratory and sedative effects of progressively increasing doses of acepromazine in conscious dogs

Abstract

Objective: To evaluate the effects of progressively increasing doses of acepromazine on cardiopulmonary variables and sedation in conscious dogs.

Study design: Prospective, experimental study.

Animals: A group of six healthy, adult, mixed-breed dogs weighing 16.5 ± 5.0 kg (mean ± standard deviation).

Methods: Dogs were instrumented with thermodilution and arterial catheters for evaluation of hemodynamics and arterial blood gases. On a single occasion, acepromazine was administered intravenously to each dog at 10, 15, 25 and 50 μg kg^-1 at 20 minute intervals, resulting in cumulative acepromazine doses of 10 μg kg^-1 (ACP₁₀), 25 μg kg^-1 (ACP₂₅), 50 μg kg^-1 (ACP₅₀) and 100 μg kg^-1 (ACP₁₀₀). Hemodynamic data and sedation scores were recorded before (baseline) and 20 minutes after each acepromazine dose.

Results: Compared with baseline, all acepromazine doses significantly decreased stroke index (SI), mean arterial pressure (MAP) and arterial oxygen content (CaO₂) with maximum decreases of 16%, 17% and 21%, respectively. Cardiac index (CI) decreased by up to 19% but not significantly. Decreases of 26-38% were recorded for oxygen delivery index (DO₂I), with significant differences for ACP₅₀ and ACP₁₀₀. Systemic vascular resistance index (SVRI) and heart rate did not change significantly. No significant difference was found among acepromazine doses for hemodynamic data. After ACP₁₀, mild sedation was observed in five/six dogs and moderate sedation in one/six dogs, whereas after ACP₂₅, ACP₅₀ and ACP₁₀₀, moderate sedation was observed in five/six or six/six dogs.

Conclusions and clinical relevance: In conscious dogs, acepromazine decreased MAP, SI, CaO₂ and DO₂I, but no significant dose effect was detected. SVRI was not significantly changed, suggesting that the reduction in MAP resulted from decreased CI. The ACP₂₅, ACP₅₀ and ACP₁₀₀ doses resulted in moderate sedation in most dogs; ACP₁₀ resulted in only mild sedation.

Keywords: canine; cardiovascular; phenothiazine derivatives; sedation; tranquilization.