Arterial blood gas tensions during recovery in horses anesthetized with apneustic anesthesia ventilation compared with conventional mechanical ventilation.

The research compared the effects of two types of ventilation, apneustic anesthesia ventilation (AAV) and conventional mechanical ventilation (CMV), on the arterial blood gas tensions in horses recovering from general anesthesia. The study concluded that while horses ventilated with AAV entered recovery with higher arterial oxygen pressure (PaO), this advantage was not maintained during recovery.

Study Design

• The study was a randomized, cross-over design involving 10 healthy adult horses from a university-owned herd.
• The horses, in a dorsally recumbent position (lying on their back), were anesthetized with isoflurane in oxygen, with the oxygen fraction initially set at 0.3. The oxygen fraction was subsequently adjusted to maintain PaO at or above 85 mmHg.
• The horses were ventilated with either AAV or CMV. Parameters for each mode for maintaining the pressure of carbon dioxide in the arteries (PaCO) were defined: 40-45 mmHg during CMV and less than 60 mmHg during AAV.
• A protocol was followed to gradually discontinue ventilation, and the horses were then moved to a stall for recovery without assistance. Blood samples were collected from the horses at predetermined time points throughout the experiment for analysis.

Results

• Data from all 10 horses were analyzed, and it was observed that the PaO in horses immediately after discontinuation of ventilation was significantly higher for those ventilated via AAV than CMV.
• However, when horses were in the sternally recumbent position (lying on their stomach), the PaO was significantly lower for those ventilated via AAV compared to CMV.
• There were no noticeable differences in PaCO between the two ventilation modes.
• All horses ventilated with CMV required additional oxygen, whereas three horses ventilated with AAV did not.
• Time taken for the horse’s first movement after recovery was shorter with AAV ventilation.
• There were no significant differences in time to oxygen insufflation between the two ventilation modes.

Conclusion

• The results suggested that although horses ventilated with AAV entered recovery with higher PaO levels, this advantage was not sustained during the recovery period.
• Also, fewer horses required supplemental oxygen after AAV ventilation. However, the usage of AAV did not eliminate the need for routine supplemental oxygen administration in horses recovering from general anesthesia.