The effect of single-prong high-flow nasal cannula therapy on CO 2 clearance

Background High-flow nasal cannula therapy has multiple proposed benefits, one of which is the clearance of exhaled CO 2 from the upper airway. The removal of exhaled CO 2 is made more difficult when the patient has a closed or partially closed mouth, as this removes or restricts the primary escape route for CO 2 -laden exhaled flow. It is proposed that this increased flush difficulty could be partially alleviated by using a single-prong cannula design, therefore allowing exhaled flow to be evacuated out of the open naris. Methods Unsteady simulations were run to investigate the effect that the proposed single-prong high-flow therapy has on CO 2 flush at intermediate and high flush difficulty scenarios. Single- and dual-prong geometries were tested under identical conditions including simulated mouth opening, respiratory cycle, airway geometry, and therapy flow setting. Therapy flows tested with both cannula geometries ranged from 12 to 45 L/min. All data discussed in this study was collected from computational models. Results The single-prong geometry resulted in less CO 2 inhalation when all other factors were equal. The distinction between cannula geometries grew as therapy flow was decreased and as the mouth opening was decreased. Pathlines, colored by residence time in the upper airway, were released from the trachea. The pathlines showed longer expiratory flow residence times in the airway for the dual-prong cannula, reinforcing the notion that that the single-prong cannula improves the efficiency of expiratory flow removal. Conclusions The results can be used to provide a framework for clinical studies investigating the potential benefits of single-prong cannulas. This would be particularly important in difficult-to-flush scenarios such as when the patient’s mouth is fully closed.