Impact of surgical masks on fraction of inspired oxygen during oxygen therapy depends on the type of oxygen masks and respiratory conditions: volunteer- and simulation-based studies

Purpose We investigated the impact of surgical masks (SM) during oxygen therapy using oxygen masks in volunteer- and simulation-based studies. Methods Fifteen volunteers wore the Hudson RCI ® or Open-Face Mask ® with/without an SM. The fraction of inspired oxygen concentration (FIO 2 ), end-tidal CO 2 (EtCO 2 ), partial pressure of inspired CO 2 (PICO 2 ), and respiratory rate (RR) were measured. The oxygen flow rate increased from 0 to 10 L/min. In the simulation-based study, FIO 2 was measured using a simulator that reproduced spontaneous breathing. RR was 12 or 24 bpm, and the tidal volume (Tv) was 300, 500, or 700 mL. The effect of oxygen mask fitting conditions was also examined. The primary outcome measure was FIO 2 at 6 L/min. Results In the volunteer-based study, FIO 2 was reduced when the SM was used with the Hudson RCI ® or Open-Face Mask ® . The FIO 2 drop was larger with the Open-Face Mask ® than with the Hudson RCI ® . The RR, EtCO 2 , and PICO 2 significantly changed with the SM, but the differences were not clinically meaningful. In the simulation-based study, the SM with the Hudson RCI ® did not reduce FIO 2 , but the SM with the Open-Face Mask ® significantly decreased FIO 2 under several conditions. However, the SM with the Hudson Mask ® reduced FIO 2 when the fit of the mask was inadequate. With the Open-Face Mask ® , lower RR and Tv resulted in larger differences in FIO 2 . Conclusions The SM decreased FIO 2 during oxygen therapy with oxygen masks. The impact of SM depended on the type of the oxygen mask, mask fitting, and respiratory condition.