Arterial oxygenation in anesthetized horses placed in a 5-degree reverse Trendelenburg position.

The research assesses the impact of the reverse Trendelenburg position versus a horizontal position on the levels of oxygen in the blood (arterial partial pressure of oxygen) in anesthetized horses, with the result showing no notable difference between the two positions.

Research Methodology

• 60 client-owned healthy horses undergoing elective surgeries were included in the study and randomized into two groups: those placed in a 5-degree Reverse Trendelenburg (RT) position and those in a horizontal (H) position. Each group contains 30 horses divided among three recumbency (lying down) positions: dorsal (on the back), right lateral (on the right side), and left lateral (on the left side).
• The horses were first sedated with butorphanol, an α-adrenoceptor agonist, in combination with acepromazine (or not), before being induced with ketamine combined with a benzodiazepine, propofol, or guaifenesin. Anesthesia was maintained via isoflurane in oxygen and controlled ventilation.
• An arterial blood gas analysis was conducted as soon as an arterial catheter was placed, and then performed on an hourly basis.

Key Evaluation Metrics

• The time from the first to the last arterial blood gas (aBG) analysis
• Changes in arterial partial pressure of oxygen (Pa0)
• Dynamic compliance (C), a measure of the lung’s ease of expansion
• Estimated pulmonary shunt fraction (F-shunt), which is the portion of blood that bypasses the lungs’ oxygenation process.
• Alveolar dead space to tidal volume ratio (V/V), a measure of non-functional circulation within the lung.

Findings of the Study

• The levels of oxygen in the blood (PaO) of all tested horses increased irrespective of the position they were placed in (RT or H).
• There was no significant statistical difference in changes over time between the two positions (RT and H) in relation to any of the key evaluation metrics: arterial oxygen pressure (PaO), dynamic compliance (C), estimated pulmonary shunt fraction (F-shunt) or alveolar dead space to tidal volume ratio (V/V).
• The study concludes that the 5-degree reverse Trendelenburg positioning does not affect changes in arterial oxygen pressure in healthy anesthetized horses compared to a horizontal position.