Study tests Trendelenburg and norepinephrine in hypovolemic horses
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A new Equine Veterinary Journal study suggests Trendelenburg positioning, especially when paired with norepinephrine infusion, can temporarily improve cardiovascular parameters in anaesthetised horses experiencing acute blood-loss hypovolemia. In the experimental study, six healthy horses under isoflurane anaesthesia were evaluated during normovolemia, induced haemorrhagic hypovolemia, and hypovolemia with norepinephrine. Trendelenburg positioning at a 30-degree incline produced modest, short-lived haemodynamic gains in normovolemic horses, but the effect was more pronounced during hypovolemia, where cardiac output rose by about 40% and mean arterial pressure by about 67%. When norepinephrine was added, improvements were greater still, with cardiac output increasing by roughly 75% during Trendelenburg positioning. The authors noted the findings are limited by the small sample size and use of healthy experimental horses rather than clinical cases. (madbarn.com)
Why it matters: Intraoperative haemorrhage is uncommon in horses, but when it happens, rapid haemodynamic support is critical. For equine veterinary teams, the study adds evidence that a simple postural maneuver may offer short-term support while fluids, transfusion planning, or vasoactive therapy are being organized. It also reinforces a broader point from equine anaesthesia literature and AAEP educational materials: maintaining arterial pressure is central to reducing anaesthetic complications, and vasoactive support is often part of that response. At the same time, Trendelenburg positioning should be viewed as a temporary adjunct, not a definitive treatment, particularly because positioning changes in horses can also affect respiratory mechanics and oxygenation. (madbarn.com)
What to watch: The next step is whether larger clinical studies in surgical horses confirm that this combined positioning-and-norepinephrine approach improves outcomes beyond short-term haemodynamic measurements. (madbarn.com)
A newly published Equine Veterinary Journal study points to a potentially useful rescue strategy for anaesthetised horses that become hypovolemic during surgery: Trendelenburg positioning, with added benefit when norepinephrine is infused at the same time. In six experimentally anaesthetised horses, investigators found the head-down position produced transient haemodynamic improvement, and that the effect was stronger during acute haemorrhagic hypovolemia than during normovolemia. The combination with norepinephrine delivered the largest gains in cardiac output and blood pressure. (madbarn.com)
The work addresses a familiar challenge in equine anaesthesia. Hypotension is a major concern in anaesthetised horses because inadequate perfusion can contribute to serious perioperative complications. AAEP proceedings have emphasized that maintaining mean arterial pressure above roughly 60 to 70 mm Hg is one of the most important elements of safe equine anaesthetic management, and dobutamine has historically been described as the most consistently useful drug for blood pressure support in this setting. More recent equine research has also examined norepinephrine’s haemodynamic effects under isoflurane anaesthesia, suggesting clinicians are continuing to look for better ways to stabilize circulation when standard support is not enough. (aaep.org)
In the new study, the horses were anaesthetised with isoflurane in dorsal recumbency and assessed under three conditions: normovolemia, acute haemorrhage-induced hypovolemia, and hypovolemia treated with norepinephrine infusion. Investigators measured cardiac output, mean arterial pressure, central venous pressure, systemic vascular resistance, mean pulmonary arterial pressure, and heart rate before, during, and after 30-degree Trendelenburg positioning. Under normovolemia, the maneuver produced modest, temporary increases in cardiac output and arterial pressure. Under hypovolemia, those effects were larger, partially reversing haemodynamic deterioration caused by blood loss. Norepinephrine alone improved cardiac output, mean arterial pressure, and systemic vascular resistance, and pairing it with Trendelenburg positioning yielded the strongest response. (madbarn.com)
The study’s practical appeal is obvious: positioning can be implemented quickly, without waiting for additional drugs or equipment. But the paper also comes with clear caveats. The sample size was small, the horses were healthy research animals, and the outcomes were physiologic rather than clinical. That means the findings support proof of concept more than practice-changing certainty. The authors explicitly caution against overgeneralizing the results to real-world surgical patients, where concurrent disease, anaesthetic depth, respiratory compromise, or ongoing blood loss may alter the response. (madbarn.com)
There’s also a balancing act between cardiovascular support and respiratory consequences. Prior work in anaesthetised horses has shown that body positioning can influence gas exchange and pulmonary mechanics. For example, a randomized clinical study of 5-degree reverse Trendelenburg found no significant improvement in arterial oxygenation compared with horizontal positioning in healthy horses, underscoring that positional effects are not uniformly beneficial and may depend on angle, indication, and patient status. That context matters when considering head-down positioning in a compromised anaesthetic patient. (pubmed.ncbi.nlm.nih.gov)
Why it matters: For veterinary professionals, this study is less about replacing established haemodynamic support than about expanding the emergency toolkit. In a horse with suspected intraoperative blood loss, Trendelenburg positioning may buy a short window to improve venous return and perfusion while the team addresses the underlying cause, adjusts anaesthetic delivery, administers fluids, or prepares blood products and vasoactive drugs. The norepinephrine finding is especially notable because it suggests a synergistic effect, although dobutamine remains deeply embedded in equine anaesthesia practice and comparative clinical data are still limited. In other words, the paper supports a potentially useful bridge strategy, not a new standard of care. (madbarn.com)
What to watch: The key question now is whether larger, clinical studies in horses undergoing actual surgery can show that these short-term haemodynamic improvements translate into better tissue perfusion, fewer anaesthetic complications, or improved recovery outcomes, and whether norepinephrine gains a clearer role alongside or against more established inotropes such as dobutamine. (madbarn.com)