Background: Dobutamine is a first-line therapy for hypotension in anesthetized horses, but effects on hemodynamic parameters in standing and anesthetized horse are not well studied.

Objectives: To investigate effects of dobutamine in escalating dosages on hemodynamic performance in awake and anesthetized horses.

Study Design: Randomized cross-over experimental study.

Methods: Six healthy adult horses were enrolled including both standing and isoflurane-anesthetized experiments with one week washout. Heart rate, mean arterial pressure (MAP), central venous pressure, pulmonary arterial pressure, and thermodilution cardiac output (CO) were measured at baseline and at dobutamine infusion rates of 0.5, 1, and 2 mcg/kg/min. Arterial and mixed-venous blood was sampled and oxygen delivery (DO₂), oxygen extraction ratio (O₂ER), and fShunt were calculated. After confirming normal distribution variables were compared to baseline and between groups using two-factorial ANOVA (alpha = 5%).

Results: MAP increased significantly during dobutamine infusion in both groups (Standing 90 ± 8 to 115 ± 7 mmHg, p < 0.001; Anesthetized 59 ± 12 to 90 ± 16 mmHg, p < 0.001), and was significantly higher in awake vs anesthetized horses at all time points (p < 0.001). CO increased significantly during dobutamine infusion (Standing 38 ± 4 to 66 ± 5 L, p < 0.001; Anesthetized 21 ± 3 to 39 ± 3 mmHg, p < 0.001), and was significantly higher in standing horses. DO₂ (p < 0.01) increased significantly and O₂ER (p < 0.001) and fShunt (p = 0.016) decreased significantly during dobutamine infusion.

Main Limitations: Small sample size; direct arterial blood pressure measurements were not feasible in awake horses.

Conclusions: Dobutamine produces a dose-dependent increase in CO and MAP and improves DO₂ under isoflurane anesthesia. Dobutamine dosages of 2 mcg/kg/min reached standing baseline MAP and CO.