Effects of surgical masks on droplet and aerosol dispersion under various oxygen delivery modalities

Takazono, T.; Yamamoto, K.; Okamoto, R.; Tashiro, M.; Morimoto, S.; Hosogaya, N.; Miyazaki, T.; Yanagihara, K.; Izumikawa, K.; Mukae, H.

Rationale Aerosol dispersion under various oxygen delivery modalities, including high flow nasal cannula, is a critical concern for healthcare workers who treat acute hypoxemic respiratory failure during the coronavirus disease 2019 pandemic. Effects of surgical masks on droplet and aerosol dispersion under oxygen delivery modalities are not yet clarified. Objectives To visualize and quantify dispersion particles under various oxygen delivery modalities and examine the protective effect of surgical masks on particle dispersion. Methods Three and five healthy men were enrolled for video recording and quantification of particles, respectively. Various oxygen delivery modalities including high flow nasal cannula were used in this study. Particle dispersions during rest breathing, speaking, and coughing were recorded and automatically counted in each condition and were evaluated with or without surgical masks. Measurements and Main Results Coughing led to the maximum amount and distance of particle dispersion, regardless of modalities. Droplet dispersion was not visually increased by oxygen delivery modalities compared to breathing at room air. With surgical masks over the nasal cannula or high-flow nasal cannula, droplet dispersion was barely visible. Oxygen modalities did not increase the particle dispersion counts regardless of breathing pattens. Wearing surgical masks significantly decreased particle dispersion in all modalities while speaking and coughing, regardless of particle sizes, and reduction rates were approximately 95 and 80-90 % for larger (> 5 m) and smaller (> 0.5 m) particles, respectively. Conclusions Surgical mask over high flow nasal canula may be safely used for acute hypoxemic respiratory failure including coronavirus disease 2019 patients.