OBJECTIVES: Nasal high-flow (NHF) therapy provides continuous positive airway pressure (CPAP), flushes the anatomical dead space, and improves mucociliary clearance. CPAP is usually applied at a flow rate at or above an established threshold value with the mouth closed because it is hard to maintain it with an open mouth. We conducted a prospective study to validate our hypothesis that CPAP can be applied with the mouth open through a surgical face mask. METHODS: We inserted 12-Fr nasogastric tubes through the noses of 18 healthy individuals and fixed each tube within the pharynx to monitor the intrapharyngeal pressure. We monitored the pressure during the following two conditions: NHF oxygen with the mouth open (condition O) and NHF oxygen with the mouth open and wearing a surgical face mask (condition OM). We set the NHF rate at 40 L/min and the oxygen concentration at 21%, under all conditions. We measured the intrapharyngeal pressure five times during each inspiration and expiration, and calculated mean values. RESULTS: The mean expiratory intrapharyngeal pressure (median [interquartile range]) increased significantly from the baseline during conditions O (2.08 [1.58–4.02] cm H(2)O) and OM (3.35 [2.72–3.79] cm H(2)O). In addition, there was a significant difference in pressure between conditions O and OM (p=0.0263, Wilcoxon signed-rank test). CONCLUSIONS: In our healthy volunteers, the intrapharyngeal pressures increased during expiration with an open mouth while wearing a surgical face mask
