LAUSR

Background During pandemic situations, many guidelines recommend that surgical masks be worn by both healthcare professionals and infected patients in healthcare settings. The purpose of this study was to clarify the levels and changes of oxygen concentration over time while oxygen was administered over a surgical mask. Methods Patients scheduled to undergo general anesthesia ( n  = 99) were enrolled in this study. First, patients were administered oxygen at 6 L/min via an oxygen mask over a surgical mask for 5 min. The patients removed the surgical mask and then took a 3-min break; thereafter, the same amount of oxygen was administered for another 5 min via the oxygen mask. We measured the fraction of inspired oxygen (FiO 2 ), the end-tidal CO 2 (EtCO 2 ), and respiratory frequency every minute for 5 min, both while administering oxygen with and without a surgical mask. The FiO 2 was measured at the beginning of inspiration and the EtCO 2 was measured at the end of expiration. Results The FiO 2 at 5 min was significantly lower when breathing with a surgical mask than that without it (mean difference: 0.08 [95% CI: 0.067–0.10]; p  <  0.001). In contrast, the EtCO 2 at 5 min was significantly higher when breathing with a surgical mask than that without it (mean difference: 11.9 mmHg [95% CI: 10.9–12.9]; p  <  0.001). Conclusion The FiO 2 was lower when oxygen was administered over surgical masks than when patients did not wear surgical masks. Oxygen flow may need to be adjusted in moderately ill patients requiring oxygen administration.