The impact of acepromazine on the efficacy of crystalloid, dextran or ephedrine treatment in hypotensive dogs under isoflurane anesthesia

To determine the impact of acepromazine on the cardiovascular responses to three treatments for hypotension in dogs during deep isoflurane anesthesia. Prospective blinded randomized cross-over experimental design. Six adult (2.5 ± 0.5 year old) healthy mixed breed dogs (24.2 ± 7.6 kg). Anesthesia was induced with propofol (4–6 mg kg−1, IV) and maintained with isoflurane. Each dog received six treatments separated by at least 5 days. Once instrumented, dogs randomly received acepromazine (0.05 mg kg−1) (Ace) or saline (equal volume) (Sal) IV and end-tidal isoflurane (e′Iso) was adjusted to achieve hypotension, defined as a mean blood pressure between 45 and 50 mmHg. Dogs randomly received dextran (D) (7 mL kg−1) or lactated Ringer's (LR) (20 mL kg−1) over 14 minutes, or ephedrine (Eph) (0.1 mg kg−1 followed by 10 μg kg−1 minute−1) throughout the study. Measurements were taken at baseline, 5, 10, 15, 20, 30, and 40 minutes. Data were analyzed with a Latin Square in two factors (Ace/Sal and treatment) for repeated measures, with further comparisons if appropriate (p < 0.05). e′Iso producing hypotension was significantly less following Ace (2.07 ± 0.23%) than Sal (2.43 ± 0.23%). No improvement in cardiac output (CO) was observed with D or LR. LR initially intensified hypotension with a significant reduction in SVR, while D caused a minor improvement in ABP. Eph produced a significant increase in ABP, CO, hemoglobin, oxygen content and delivery. Pre-treatment with Ace minimized ABP improvements with all treatments. Acepromazine (0.05 mg kg−1 IV) enhanced the hypotensive effect of isoflurane, although it maintained CO. Administration of LR significantly worsens ABP initially by further vasodilation. D caused minimal improvement in ABP. At the infusion studied, Eph effectively countered the cardiovascular depression produced by deep isoflurane anesthesia, but extremes in ABP associated with initial vasoconstriction prevent our recommendation at this dose.