Effects of continuous positive airway pressure (CPAP) on respiratory function in sedated foals

Objective

To characterize the effects of continuous positive airway pressure (CPAP) delivered by a commercial human CPAP device on respiratory function in foals with pharmacologically induced respiratory suppression.

Design

Prospective randomized, cross-over study comparing CPAP with spontaneous respiration and oxygen insufflation.

Setting

University veterinary teaching hospital.

Animals

Twelve foals born in consecutive seasons from a university teaching herd.

Interventions

Foals were randomized to receive 10 minutes of respiratory support by mask oxygen supplementation or CPAP as a first treatment after induction of respiratory depression by intravenous administration of xylazine and fentanyl. Each foal received the alternate treatment after 10 minutes of breathing ambient air, and the procedure was repeated after 48 hours with treatment order reversed.

Measurements and main results

The administration of xylazine and fentanyl by bolus or continuous infusion reliably induced reversible respiratory suppression and recumbency. CPAP was associated with comparable increase in PaO₂ relative to mask oxygen supplementation, but with lower respiratory rate, increased oxygen extraction and increased carbon dioxide elimination. Mild increase in PaCO₂ was observed during CPAP and O₂ supplementation. Expiratory time increased and peak expiratory flow decreased during CPAP.

Conclusions

Findings of the study suggest that CPAP might represent a method for improved respiratory support compared to O₂ insufflation due to increased respiratory efficiency. Care must be taken in extrapolation of these findings from foals with pharmacologically induced respiratory compromise to foals with clinical respiratory disease, and further investigation is required to better characterize the cause and impact of marginal hypercapnia observed in these studies.