Effects of breathing pattern on oxygen delivery via a nasal or pharyngeal cannula

Abstract

BACKGROUND: During sedation for upper gastrointestinal endoscopy, oxygen delivery via a nasal cannula is often necessary. However, the influences of the oxygen delivery route and breathing pattern on the FIO2 have not been thoroughly investigated. The aim of this simulation study was to investigate the difference in the FIO2 with a pharyngeal cannula versus nasal cannula during high-or low-tidal volume (VT) ventilation and openor closed-mouth breathing. METHODS: Six healthy volunteers were asked to breathe using 2 patterns of ventilation (high or low VT) via a sealed face mask connected to an endotracheal tube that was retrogradely inserted into the trachea of a mannequin. The mannequin also had a pharyngeal or nasal cannula inserted into the pharynx or attached to the nose, through which oxygen (2 or 5 L/min) was delivered. The mouth of the mannequin was kept open or closed by packing. We measured the FIO2 of every breath for 1 min at each setting. RESULTS: During low- and high-VT ventilation, the FIO2was highest at a flow of 5 L/min with a pharyngeal cannula. Oxygen delivery was higher with the pharyngeal cannula compared with the nasal cannula at all settings. Differences in flow did not result in significant differences in the FIO2 with high- and low-VT ventilation. At a flow of 5 L/min via a pharyngeal cannula, open-mouth breathing resulted in a significantly higher FIO2 compared with closed-mouth breathing. Conclusions: A pharyngeal cannula provided a higher FIO2 compared with a nasal cannula at the same oxygen flow. Open-mouth breathing resulted in a higher FIO2 compared with closed-mouth breathing when 5 L/min oxygen was delivered via a pharyngeal cannula. The breathing pattern did not affect the FIO 2 in this study.