Effect of reducing inspired oxygen concentration on oxygenation parameters during general anaesthesia in horses in lateral or dorsal recumbency.

This study examines the effect of reducing oxygen concentration on oxygen levels in the body of horses during general anesthesia, particularly paying attention to the horses’ positioning (lateral or dorsal recumbency). The findings suggest that using a concentration of 60% oxygen, instead of 100%, during anaesthesia can maintain adequate oxygenation in the horses, regardless of their position. However, this reduction won’t alleviate the pulmonary function abnormalities brought about by anesthesia and recumbency.

Methods of the Study

• The study involved 24 horses, positioned in either lateral or dorsal recumbency, during the general anesthesia.
• These horses were split into two groups randomly, with one group receiving 100% oxygen, and the other 60% oxygen during anesthesia.
• All the horses were anaesthetised using the same protocol, with intermittent positive pressure ventilation (IPPV) starting immediately after anaesthetic induction and endotracheal intubation.
• The researchers monitored selected respiratory parameters and blood lactate levels before and during Anaesthesia.
• Arterial blood gas analysis was performed several times – before premedication, immediately after induction, at 10 and 45 minutes after the commencement of mechanical ventilation, and in recovery.

Results of the Study

• The findings showed that during anaesthesia, the arterial partial pressure of oxygen was adequate in all horses, regardless of their positioning or the oxygen concentration provided.
• At 10 and 45 minutes after starting IPPV, the arterial partial pressure of oxygen was lower in horses in dorsal recumbency (on their back) compared to those in lateral recumbency (on their side).
• Interestingly, this was the case irrespective of the concentration of oxygen supplied.
• When examining oxygenation indices (a measure of how well oxygen is being distributed to the tissues), it was found that the pulmonary function during general anesthesia in horses placed on their back (dorsal recumbency) was more compromised than those placed on their side (lateral recumbency).

Conclusions of the Study

• The study concludes that during general anesthesia, using a lower concentration of 60% oxygen – instead of 100% – maintains adequate arterial oxygenation in horses, no matter whether they’re positioned on their side or back.
• However, this reduction in oxygen concentration does not appear to reduce abnormalities in lung (pulmonary) function that are induced by the anaesthesia and the horse’s position.