Continuous positive airway pressure (CPAP) decreases pulmonary shunt in anaesthetized horses.

The research assessed the influence of continuous positive airway pressure (CPAP) on intrapulmonary shunt, cardiac output, and oxygen delivery in horses that are anaesthetised for a long duration. The result of this study found that CPAP effectively reduced the pulmonary shunt fraction in these horses without any noticeable decrease in their cardiac output.

Methods and Procedures

• The study involved ten adult horses that were healthy. It was a crossover type experiment with randomization.
• The horses were anesthetized using a combination of medetomidine, diazepam, and ketamine, after which an orotracheal intubation procedure was performed.
• They were then laid on their backs (in dorsal recumbency). The anaesthesia was maintained with isoflurane, which was carried in a mixture of air and oxygen, along with a medetomidine infusion.
• The horses were subjected to a 6-hour period of general anaesthesia twice. In these sessions, either CPAP of 8cmH O or physiological airway pressure (NO CPAP) was applied to their lungs. The order of treatments was randomly assigned.
• Arterial blood gas analysis, along with other cardiovascular and respiratory variable monitoring was done every 30 minutes after inducing the anesthesia. Cardiac output was also measured every hour using the lithium dilution technique.
• If the partial pressure of carbon dioxide in their arterial blood (PaCO) exceeded 100 mmHg, controlled ventilation was initiated. Horses that reached this threshold were omitted from further data collection.
• A comparison between the CPAP group and the NO CPAP group was made using a general linear model.

Results and Conclusion

• Results obtained from eight horses were analysed. It was noted that the partial pressure of oxygen in their blood (PaO) was 2.00-7.45 kPa (15-56 mmHg) higher in the CPAP group as compared to the NO CPAP group. The shunt fraction was also 6-14% lower in this group.
• No significant variations were noticed in cardiac output and oxygen delivery between the two groups.
• The lack of difference in oxygen delivery is ascribed to the lower levels of haemoglobin in the group that was administered CPAP in comparison to the NON-CPAP group.
• From the collected data, the researchers concluded that CPAP with a pressure of 8 cmH O is effective in reducing the pulmonary shunt fraction in horses laid on their backs. This reduction was seen without any noticeable decrease in their cardiac output when the horses were subjected to long-term anaesthesia.