The effect of dobutamine and bolus crystalloid fluids on the cardiovascular function of isoflurane-anaesthetised horses.
Authors: Loughran C M, Raisis A L, Hosgood G, Secombe C J, Lester G D
Journal: Equine veterinary journal
Summary
# Editorial Summary During isoflurane anaesthesia, maintaining adequate cardiovascular support in hypotensive horses presents a clinical challenge, particularly regarding whether inotropic support alone achieves meaningful peripheral perfusion. This randomised cross-over study compared dobutamine infusion (0.5–adjusted μg/kg bwt/min to target MAP 80 mmHg) against the same dobutamine protocol combined with a 20 mL/kg bolus of Hartmann's solution in six anaesthetised horses, measuring cardiac index, oxygen delivery, haemoglobin concentration and bilateral femoral arterial blood flow at baseline, 30 minutes post-treatment and 15 minutes post-cessation. Dobutamine alone significantly improved oxygen delivery index and arterial oxygen content through haemoconcentration, though cardiac output remained unchanged—a finding consistent with clinical concern about dobutamine's variable efficacy in anaesthetised horses. The addition of crystalloid fluids produced a markedly different response, with significant increases in upper and lower limb femoral blood flow at the 30-minute mark, despite similar haemoglobin and oxygen content profiles to dobutamine monotherapy. Haemoglobin and arterial oxygen content remained significantly elevated 15 minutes after dobutamine cessation regardless of fluid administration. For equine anaesthetists, these results suggest that combining crystalloid bolus with dobutamine may better support peripheral tissue perfusion—particularly to limb musculature—than inotropic support alone, warranting consideration during prolonged procedures or in horses at high risk of postoperative myopathy.
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Practical Takeaways
- •When using dobutamine to support blood pressure in anaesthetised horses, adding a crystalloid bolus may improve peripheral muscle perfusion via increased femoral blood flow, potentially reducing tissue ischaemia despite lower haemoglobin levels
- •Dobutamine alone improves oxygen carrying capacity but does not increase cardiac output—expect maintained rather than improved heart pumping function
- •Choose combination therapy (dobutamine + fluids) if peripheral tissue perfusion is a clinical concern; use dobutamine alone if maintaining oxygen content is the priority
Key Findings
- •Dobutamine alone increased oxygen delivery index (DO2I), arterial oxygen content (CaO2), and haemoglobin concentration but did not increase cardiac index in hypotensive anaesthetised horses
- •Combined dobutamine and crystalloid fluid bolus (20 mL/kg) significantly increased femoral blood flow in both upper (P=0.005) and lower limbs (P=0.042) compared to dobutamine alone
- •Haemoglobin concentration and arterial oxygen content were significantly higher during dobutamine-only treatment at T1 and T2, suggesting fluid dilution effect in combination treatment
- •Cardiac index did not change with either dobutamine alone or combined dobutamine plus crystalloid fluid therapy