Modified N95 Mask Delivers High Inspired Oxygen Concentrations While Effectively Filtering Aerosolized Microparticles

STUDY OBJECTIVE: In a pandemic, hypoxic patients will require an effective oxygen (O(2)) delivery mask that protects them from inhaling aerosolized particles produced by others, as well as protecting the health care provider from exposure from the patient. We modified an existing N95 mask to optimize O(2) supplementation while maintaining respiratory isolation. METHODS: An N95 mask was modified to deliver O(2) by inserting a plastic manifold consisting of a 1-way inspiratory valve, an O(2) inlet and a gas reservoir. In a prospective repeated-measures study, we studied 10 healthy volunteers in each of 3 phases, investigating (1) the fractional inspiratory concentrations of O(2) (F(I)O(2)) delivered by the N95 O(2) mask, the Hi-Ox(80) O(2) mask, and the nonrebreathing mask during resting ventilation and hyperventilation, each at 3 O(2) flow rates; (2) the ability of the N95 mask, the N95 O(2) mask, and the nonrebreathing mask to filter microparticles from ambient air; and (3) to contain microparticles generated inside the mask. RESULTS: The F(I)O(2)s (median [range]) delivered by the Hi-Ox(80) O(2) mask, the N95 O(2) mask, and the nonrebreathing mask during resting ventilation, at 8 L/minute O(2) flow, were 0.90 (0.79 to 0.96), 0.68 (0.60 to 0.85), and 0.59 (0.52 to 0.68), respectively. During hyperventilation, the FiO(2)s of all 3 masks were clinically equivalent. The N95 O(2) mask, but not the nonrebreathing mask, provided the same efficiency of filtration of internal and external particles as the original N95, regardless of O(2) flow into the mask. CONCLUSION: An N95 mask can be modified to administer a clinically equivalent FiO(2) to a nonrebreathing mask while maintaining its filtration and isolation capabilities.