Dobutamine improves haemodynamics and oxygen delivery in standing and isoflurane-anaesthetised horses.

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

Objectives: To investigate the effects of dobutamine in escalating dosages on haemodynamic performance in awake and anaesthetised horses.

Study design: Randomised cross-over experimental study.

Methods: Six healthy adult horses were enrolled, including both standing and isoflurane-anaesthetised experiments with 1-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 (O₂ ER), and fShunt were calculated. After confirming normal distribution, variables were compared with baseline and between groups using two-factorial ANOVA (alpha = 5%).

Results: MAP increased significantly during dobutamine infusion in both groups (Standing 92 ± 8 to 119 ± 8 mmHg, p < 0.001; Anaesthetised 58 ± 12 to 91 ± 16 mmHg, p < 0.001), and was significantly higher in awake versus anaesthetised horses at all time points (p < 0.001). CO increased significantly during dobutamine infusion (Standing 39 ± 5 to 68 ± 5 L/min, p < 0.001; Anaesthetised 21 ± 2 to 38 ± 3 L/min, p < 0.001), and was significantly higher in standing horses (p < 0.001). DO₂ (p < 0.001) increased significantly, and O₂ ER (p < 0.001) decreased significantly in both groups with dobutamine infusion. FShunt (p = 0.02) decreased significantly during dobutamine infusion in anaesthetised horses.

Main limitations: Small sample size; study performed in a lateral recumbency.

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