The N95 or higher-level respirator is an essential element of personal protective equipment to be worn when in contact with patients with known or suspected coronavirus disease 2019 (COVID-19) infection. Three varieties are commonly available: preformed/cup, flat fold/duck bill, and elastomeric. Wearing an N95 mask invokes a number of physiologic implications, particularly with prolonged use (greater than 1 h), higher workloads, or an overlying surgical mask (table 1).2,3  Concomitant surgical mask use augments the impact of a cup mask due to further resistance to airflow, but diminishes the impact of a flat fold mask due to a reduction in deadspace.

At 2 metabolic equivalents (e.g., walking slowly during rounds), N95 mask use noticeably increases inhaled carbon dioxide, reduces inspired oxygen, and increases the work of breathing. The resulting...

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