Dobutamine and ephedrine are commonly administered to anesthetized horses to increase arterial blood pressure. Dobutamine administered at 3 and 5 ug/kg/min has been shown to increase hemoglobin concentration in anesthetized horses. Ephedrine (0.25 mg/kg) significantly increased hemoglobin concentration in anesthetized dogs. The purpose of this study was to determine if dobutamine or ephedrine would increase packed cell volume (PCV) and total plasma protein concentration (TP) in clinical equine cases anesthetized using a variety of anesthetic techniques. Horses were premedicated with xylazine, administered either guaifenesin or diazepam, and induced with either thiopental or ketamine. Anesthetic protocols were not different between treatment groups. The horses were administered intravenous fluids at approximately 10 ml/kg/hr. Following baseline measurement of mean arterial pressure (MAP), heart rate (HR), PCV, and TP, a constant rate infusion of dobutamine or a bolus of ephedrine was administered to hypotensive (MAP < 65 mmHg) anesthetized horses. Dobutamine was administered to 28 horses which were 6.0 ± 4.8 (mean ± SD) years of age and weighed 443 ± 99 kg. Ephedrine was administered to 13 horses which were 3.3 ± 3.9 years of age and weighed 399 ± 128 kg. Dobutamine was administered at a rate of 1-2 ug/kg/min (n = 24) or 2-4 ug/kg/min (n = 4), and ephedrine was administered at a dose of 0.06-0.12 mg/kg (n = 13). MAP, HR, PCV, and TP were measured again at 5 and 15 minutes. The effect of treatment over time was analyzed using a two-way ANOVA for repeated measures. The volume of intravenous fluid administered was not statistically different between the two groups during the study period. Dobutamine significantly (P < 0.05) increased MAP from 49 ± 7 to 63 ± 11 and 71 ± 9 mmHg at 5 and 15 minutes, respectively (mean ± SD). Ephedrine significantly (P < 0.05) increased MAP from 50 ± 5 to 57 ± 6 and 62 ± 7 mmHg at 5 and 15 minutes, respectively. HR did not change in either group. Dobutamine significantly (P < 0.05) increased PCV from 30 ± 6 at baseline to 36 ± 7% at 15 minutes. Baseline PCV (31 ± 4%) was not significantly different from 15 minutes (32 ± 4%) in ephedrine-treated horses. TP (g/dl) did not change significantly in either group. These results suggest that PCV is likely to increase in anesthetized horses administered dobutamine.
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