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Equine veterinary journal2026; doi: 10.1002/evj.70313

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

Abstract: Perianaesthetic fluid therapy can influence oxygen delivery and tissue oxygenation, yet the optimal fluid rate in horses remains undefined. Objective: To compare two fluid strategies on peripheral tissue oxygenation (StO) and cardiorespiratory variables in isoflurane-anaesthetised horses. Methods: Randomised, controlled, experimental design with two independent groups. Methods: Sixteen euvolemic adult horses undergoing coeliotomy were anaesthetised with xylazine, ketamine, and midazolam, maintained on isoflurane with lidocaine infusion, and randomised to lactated Ringer's solution at 2.5 mL/kg/h (maintenance; MNT) or 40 mL/kg/h (high fluids; HF) for 120 min. StO was measured at the extensor carpi radialis muscle using near-infrared spectroscopy. Heart rate, mean arterial pressure (MAP), central venous pressure (CVP), cardiac output (CO), serum lactate, and urine output were recorded at baseline, 60, and 120 min and analysed using mixed-effects linear regression and Bland-Altman repeated-measures correlation. Results: StO increased over time in both groups (p ≤ 0.018) and weakly correlated with MAP (ρ = 0.36, p = 0.0498) and lactate (ρ = 0.36, p = 0.05), but not with ScvO or PvO (p > 0.88). HF had significantly higher median MAP (80 vs. 76 and 79 vs. 72 mmHg), CVP (7.5 vs. 2.7 and 17.0 vs. 4.0 mmHg), serum lactate concentrations at 60 and 120 min, respectively (3.0 vs. 1.4; 2.8 vs. 1.3 mmol/L) and total urine output (0.72 vs. 0.37; mL/kg/h) than MNT (all p < 0.001). CO increased over time in MNT but not HF. No differences were detected in StO, CO, ScvO, or PvO between groups. Conclusions: Small sample size and short observation window. Conclusions: High-rate fluid therapy increased MAP, CVP, and urine output not StO or CO, and was associated with higher serum lactate. Tissue oxygenation improved over time regardless of fluid rate, suggesting limited benefit of aggressive crystalloid administration in anaesthetised euvolemic horses.
© 2026 EVJ Ltd.
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Publication Date: 2026-09-02 PubMed ID: 42686675DOI: 10.1002/evj.70313Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

  • This study compared the effects of two intravenous fluid administration rates on tissue oxygenation and cardiovascular stability in horses under anesthesia.
  • It aimed to determine if high fluid rates improve tissue oxygen delivery or cardiovascular function compared to more moderate rates.

Background

  • During anesthesia, maintaining adequate tissue oxygenation is critical to prevent organ dysfunction.
  • Fluid therapy influences blood volume and flow, which can affect oxygen delivery to tissues.
  • In horses, the optimal fluid administration rate during anesthesia remains unclear.

Study Design and Methods

  • Sixteen adult horses undergoing abdominal surgery (coeliotomy) under anesthesia were studied.
  • All horses were anesthetized with xylazine, ketamine, and midazolam, maintained with isoflurane and lidocaine infusion.
  • Horses were randomly assigned to one of two fluid therapy groups:
    • Maintenance group (MNT): lactated Ringer’s solution at 2.5 mL/kg/h
    • High fluid group (HF): lactated Ringer’s solution at 40 mL/kg/h
  • Fluids were administered for 120 minutes during anesthesia.
  • Peripheral tissue oxygenation (StO) was measured noninvasively on the extensor carpi radialis muscle using near-infrared spectroscopy.
  • Other measurements at baseline, 60 and 120 minutes included:
    • Heart rate
    • Mean arterial pressure (MAP)
    • Central venous pressure (CVP)
    • Cardiac output (CO)
    • Serum lactate concentration
    • Urine output
  • Data were analyzed using mixed-effects linear regression and correlations between variables were assessed.

Key Findings

  • Tissue oxygenation (StO):
    • Increased over time in both fluid rate groups, indicating improved oxygen delivery during anesthesia.
    • No significant difference in StO between high fluid and maintenance fluid groups.
  • Cardiovascular parameters:
    • MAP and CVP were significantly higher in the high fluid group at 60 and 120 minutes compared to maintenance.
    • Cardiac output increased over time only in the maintenance group; no increase was seen in the high fluid group.
  • Serum lactate:
    • Higher lactate levels observed in the high fluid group at both 60 and 120 minutes, suggestive of altered metabolism or tissue perfusion.
  • Urine output:
    • Higher total urine output was found in the high fluid group, consistent with greater fluid administration.
  • Correlations:
    • StO showed weak positive correlations with MAP and serum lactate but was not correlated with central or peripheral venous oxygen content (ScvO or PvO).

Conclusions and Implications

  • High-rate fluid administration increased blood pressure, venous pressure, and urine production but did not improve cardiac output or tissue oxygenation compared to maintenance fluid rates in anesthetized horses.
  • The increase in serum lactate with high fluid rates may indicate metabolic stress or inadequate tissue perfusion despite higher pressures.
  • Tissue oxygenation improved over time regardless of fluid rate, suggesting that aggressive crystalloid fluid therapy offers limited benefit in otherwise euvolemic (normal blood volume) anesthetized horses.
  • The findings argue for cautious use of large fluid volumes during equine anesthesia and highlight the need to individualize fluid therapy rather than rely on high-volume infusion to optimize oxygen delivery.
  • Limitations include small sample size and short duration of observation, warranting further research for definitive recommendations.

Cite This Article

APA
Moura RA, Bisiau A, Freeman D, Grosche A, Azevedo TMBPR, Vettorato E, Portela DA, Chiavaccini L. (2026). Effects of two different fluid rates on tissue oxygenation and haemodynamic stability in anaesthetised horses. Equine Vet J. https://doi.org/10.1002/evj.70313

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English

Researcher Affiliations

Moura, Raiane A
  • Department of Large Animal Clinical Sciences, University of Florida, College of Veterinary Medicine, Gainesville, Florida, USA.
Bisiau, Amber
  • Department of Large Animal Clinical Sciences, University of Florida, College of Veterinary Medicine, Gainesville, Florida, USA.
Freeman, David
  • Department of Large Animal Clinical Sciences, University of Florida, College of Veterinary Medicine, Gainesville, Florida, USA.
Grosche, Astrid
  • Department of Large Animal Clinical Sciences, University of Florida, College of Veterinary Medicine, Gainesville, Florida, USA.
Azevedo, Tatiana Moreira B P R
  • Department of Comparative, Diagnostic and Population Medicine, University of Florida, College of Veterinary Medicine, Gainesville, Florida, USA.
Vettorato, Enzo
  • Department of Comparative, Diagnostic and Population Medicine, University of Florida, College of Veterinary Medicine, Gainesville, Florida, USA.
Portela, Diego A
  • Department of Comparative, Diagnostic and Population Medicine, University of Florida, College of Veterinary Medicine, Gainesville, Florida, USA.
Chiavaccini, Ludovica
  • Department of Comparative, Diagnostic and Population Medicine, University of Florida, College of Veterinary Medicine, Gainesville, Florida, USA.

Grant Funding

  • Arden and Claudia Sims

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