Effects of two different intraoperative fluid rates on tissue oxygenation and haemodynamic stability in anaesthetised horses

Abstract

<p><strong>Background:</strong><br> Perianaesthetic fluid therapy influences tissue perfusion and oxygen delivery, but its effects in horses remain unclear.</p> <p><strong>Objectives:</strong><br> To evaluate the impact of two intraoperative fluid administration rates on peripheral tissue oxygenation (StO₂) and cardiorespiratory parameters in isoflurane-anaesthetised horses.</p> <p><strong>Study design:</strong><br> In vivo, randomised experimental study.</p> <p><strong>Methods:</strong><br> Sixteen adult horses undergoing experimental coeliotomy were anaesthetised with xylazine, ketamine and midazolam, and maintained on isoflurane with a lidocaine constant rate infusion. Horses were randomly assigned to receive lactated Ringer’s solution at either 2.5 mL kg⁻¹ h⁻¹ (MNT) or 40 mL kg⁻¹ h⁻¹ (OHD) for 120 minutes. Peripheral StO₂ was measured at the extensor carpi radialis muscle using near-infrared spectroscopy. Heart rate, respiratory rate, mean arterial pressure (MAP), central venous pressure (CVP), cardiac output (CO) and serum lactate were recorded at baseline, and at 60 and 120 minutes after fluid administration. Data were analysed using mixed-effects linear regression. Correlations between StO₂ and physiological variables were assessed using Bland–Altman repeated-measures correlation. Significance was set at p ≤ 0.05.</p> <p><strong>Results:</strong><br> StO₂ increased over time in both groups (p = 0.019), with no significant interaction between time and fluid rate (LR χ² = 1.49, p = 0.47). MAP, CVP and lactate concentrations were significantly higher in the OHD group at 60 and 120 minutes (p &lt; 0.01). CO increased over time in the MNT group and slightly declined in the OHD group, indicating a significant interaction (LR χ² = 8.27, p = 0.016). StO₂ was weakly but significantly correlated with MAP and lactate (ρ = 0.36, p = 0.05).</p> <p><strong>Main limitations:</strong><br> Limited sample size and short observation window may have influenced results.</p> <p><strong>Conclusions:</strong><br> StO₂ increased over time regardless of fluid rate. OHD improved MAP and CVP but did not enhance StO₂ or CO.</p>

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