evidence: The study sample size was calculated with PASS 11 (NCSS, LLC Kaysville, UT, USA). Before the release of the electronic questionnaire, we conducted a small-scale preliminary survey. The incidence of wearing SMs continuously for morethan 4 h was 55%. We assumed that the incidence was 50%, with α of 5%, absolute deviation of 5%, and the sample size of 402. Previous studies have shown that masks can reduce the blood oxygen saturation of medical staff by 1–3.5% (20, 21). We determined whether wearing an SM was associated with an SpO2 decrease of 2% or more. For a 2% decrease in SpO2, a standard deviation of 3%, α of 5%, and power of 90%, a sample size of at least 24 participants was required. Considering the 10% shedding rate, at least 27 participants were required. According to the inclusion and exclusion criteria, we included 39 anesthesiologists. One participant whose resting oxygen saturation reading was lower than 96% and 3 participants who did not complete the test due to removing their masks were excluded, and a total of 35 subjects were included.