Effect of 15° Reverse Trendelenburg Position on Arterial Oxygen Tension during Isoflurane Anesthesia in Horses.
Authors: Tucker Laura, Almeida Daniel, Wendt-Hornickle Erin, Baldo Caroline F, Allweiler Sandra, Guedes Alonso G P
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary Hypoxaemia remains a persistent challenge during equine general anaesthesia, prompting investigation into positional strategies that might improve arterial oxygen tension without altering anaesthetic depth. This randomised, crossover study compared horizontal positioning with 15° reverse Trendelenburg positioning in six dorsally recumbent horses anaesthetised with isoflurane and mechanically ventilated, measuring arterial blood gas parameters and calculating oxygenation indices at 30-minute intervals over two hours. In five horses, reverse Trendelenburg significantly improved PaO₂ (median 502 mmHg versus 437 mmHg, *p* = 0.03), P-F ratio and intrapulmonary shunting compared with horizontal positioning, suggesting that head-up positioning enhances ventilation-perfusion matching during dorsal recumbency. However, one horse with atypical thoracic conformation exhibited worsened oxygenation in reverse Trendelenburg, highlighting inter-individual variation in response that warrants consideration. Whilst these findings are encouraging for clinical application—particularly for lengthy procedures where hypoxaemia poses significant risk—the authors appropriately call for cardiovascular assessment before formal recommendation, as mean arterial pressure support requirements may differ between positions and could influence overall anaesthetic safety and post-operative recovery.
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Practical Takeaways
- •Consider positioning dorsally recumbent anesthetized horses in 15° reverse Trendelenburg to improve oxygen tension during isoflurane anesthesia, though individual response may vary
- •Be aware that horses with certain thoracic conformations may not benefit from or may worsen with reverse Trendelenburg positioning—monitor oxygenation parameters individually
- •Cardiovascular effects of reverse Trendelenburg positioning require further study before routine clinical adoption
Key Findings
- •15° reverse Trendelenburg position significantly improved arterial oxygen tension (PaO2 502 vs 437 mmHg) compared to horizontal position in anesthetized horses
- •P-F ratio (oxygenation index) was significantly better in reverse Trendelenburg position (518 vs 455 mmHg)
- •Pulmonary shunt fraction was significantly reduced in reverse Trendelenburg position (10.1 vs 14.2 mmHg)
- •One horse showed worsened oxygenation in reverse Trendelenburg position, suggesting individual variation based on thoracic conformation