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Equine veterinary journal2026; doi: 10.1002/evj.70169

Trendelenburg positioning with or without norepinephrine infusion for haemodynamic support in anaesthetised hypovolemic horses.

Abstract: Intraoperative haemorrhage during equine anaesthesia is a rare but potentially fatal complication requiring prompt haemodynamic support. Postural manoeuvres such as Trendelenburg (TL) positioning and vasopressor support augment venous return and improve cardiac output (CO), yet their efficacy in anaesthetised hypovolemic horses remains unstudied. Objective: To evaluate haemodynamic effects of TL positioning during normovolemia and acute haemorrhagic hypovolemia, and to determine whether concurrent norepinephrine (NE) infusion enhances cardiovascular stabilisation. Methods: In vivo experiments. Methods: Six dorsally recumbent isoflurane-anaesthetised horses were studied under normovolemia, acute haemorrhage-induced hypovolemia, and hypovolemia with NE infusion. Haemodynamic variables, including CO, mean arterial pressure (MAP), central venous pressure (CVP), systemic vascular resistance (SVR), mean pulmonary arterial pressure (mPAP), and heart rate (HR), were recorded at multiple timepoints before, during, and after TL positioning (30° incline). Norepinephrine was administered at 0.1 μg/kg/min to restore MAP above 80 mmHg. Results: Trendelenburg positioning during normovolemia resulted in modest, transient increases in CO (~28%), MAP (~22%), CVP, and mPAP (p < 0.05), with no change in HR and SVR. Haemorrhagic hypovolemia significantly reduced all haemodynamic indices (p < 0.01) except HR and SVR. TL positioning partially reversed these effects (increase in CO ~40% and MAP ~67%; p < 0.05). Norepinephrine infusion alone during hypovolemia significantly increased CO, MAP, and SVR, with additional improvement when combined with TL positioning (increase in CO ~75%; p < 0.05), suggesting enhanced effects. Conclusions: Small sample size and use of healthy experimental animals limit translational generalisability of the findings to clinical populations. Conclusions: TL positioning transiently improves haemodynamics in anaesthetised horses, with more pronounced benefits during hypovolemia. The addition of NE infusion enhances this effect, supporting their combination as a potential physiologic rescue strategy in hypovolemic equine patients.
© 2026 The Author(s). Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.
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Publication Date: 2026-04-19 PubMed ID: 42002690DOI: 10.1002/evj.70169Google Scholar: Lookup
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  • Journal Article

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.

Research Overview

  • This study investigates how Trendelenburg (head-down tilt) positioning affects heart and blood circulation functions in anesthetised horses with normal and low blood volume due to bleeding.
  • It also examines whether adding a norepinephrine infusion, a drug that constricts blood vessels and supports blood pressure, improves cardiovascular stability in these horses.

Background

  • Intraoperative hemorrhage (bleeding during surgery) in horses under anesthesia is rare but can be life-threatening.
  • Timely interventions to support blood circulation—such as positioning the horse’s body to improve blood return to the heart or using drugs to increase blood pressure—are critical to manage this condition.
  • Trendelenburg (TL) positioning involves tilting the horse’s body at about a 30° incline with the head down, theoretically promoting venous return, increasing cardiac output (CO), and improving blood pressure.
  • Norepinephrine (NE) is a vasopressor drug that can increase blood vessel constriction, boosting mean arterial pressure (MAP) and potentially improving cardiac function during hypovolemia (low blood volume).
  • Despite these known mechanisms, the effectiveness of TL positioning alone or combined with NE infusion in anesthetised, hypovolemic horses had not been evaluated before this study.

Study Objectives

  • To assess how TL positioning affects haemodynamic (cardiovascular) parameters in horses both with normal blood volume and in acute hemorrhagic hypovolemia during anesthesia.
  • To determine whether co-administration of norepinephrine improves cardiovascular stabilization beyond TL positioning alone.

Methods

  • Subjects: Six healthy horses under isoflurane anesthesia positioned dorsally (on their backs).
  • Conditions studied:
    • Normovolemia (normal blood volume).
    • Acute hemorrhagic hypovolemia induced by blood removal.
    • Hypovolemia with norepinephrine infusion (at 0.1 μg/kg/min).
  • Procedure: TL positioning was applied at a 30° incline.
  • Measurements: Heart rate (HR), cardiac output (CO), mean arterial pressure (MAP), central venous pressure (CVP), systemic vascular resistance (SVR), and mean pulmonary arterial pressure (mPAP) were recorded repeatedly before, during, and after TL positioning.
  • Norepinephrine infusion was used to raise MAP above 80 mmHg during hypovolemia.

Results

  • During normovolemia:
    • Trendelenburg positioning caused modest and temporary increases:
      • Cardiac output increased by approximately 28%.
      • Mean arterial pressure increased by approximately 22%.
      • Central venous pressure and pulmonary arterial pressure also increased significantly.
      • No significant change in heart rate or systemic vascular resistance.
  • During haemorrhagic hypovolemia:
    • All cardiovascular variables except HR and SVR significantly decreased, confirming the effects of blood loss on heart and vessel function.
    • Trendelenburg positioning partially reversed these reductions, increasing:
      • Cardiac output by about 40%.
      • Mean arterial pressure by about 67%.
  • Norepinephrine infusion during hypovolemia:
    • Significantly increased cardiac output, mean arterial pressure, and systemic vascular resistance on its own.
    • The combination of TL positioning plus NE infusion provided further improvement, with cardiac output increasing by about 75%.
    • This suggests an additive or synergistic effect of the two interventions.

Conclusions

  • Trendelenburg positioning transiently improves haemodynamics in anesthetised horses, more so during states of low blood volume caused by hemorrhage.
  • Norepinephrine infusion enhances these positive effects, supporting the combination of postural change and drug therapy as a physiologic rescue approach for hypovolemic equine patients.
  • Limitations:
    • The study had a small sample size (six horses), which affects how broadly the results can be applied.
    • The horses were healthy experimental animals, so findings may differ in clinical populations with different health statuses or co-morbidities.

Summary

  • This research supports the use of Trendelenburg positioning combined with norepinephrine infusion as a potential emergency treatment to stabilize circulation in anesthetised horses experiencing acute blood loss.
  • Further research with larger and more clinically diverse populations is needed to confirm and expand upon these findings.

Cite This Article

APA
Paranjape VV, Hopster K, Lutvikadic I, Driessen B. (2026). Trendelenburg positioning with or without norepinephrine infusion for haemodynamic support in anaesthetised hypovolemic horses. Equine Vet J. https://doi.org/10.1002/evj.70169

Publication

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

Researcher Affiliations

Paranjape, Vaidehi V
  • Department of Small Animal Clinical Sciences, Virginia-Maryland College of Veterinary Medicine, Blacksburg, Virginia, USA.
Hopster, Klaus
  • Department of Clinical Studies-New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, Pennsylvania, USA.
Lutvikadic, Ismar
  • Department of Clinical Studies-New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, Pennsylvania, USA.
  • Department of Clinical Science, University of Sarajevo-Veterinary Faculty, Sarajevo, Bosnia and Herzegovina.
Driessen, Bernd
  • Department of Clinical Studies-New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, Pennsylvania, USA.

Grant Funding

  • 181297 / Virginia-Maryland College of Veterinary Medicine-Equine Research Competition Grants Program

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