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Comparative Study
. 2006 Oct;48(4):391-9, 399.e1-2.
doi: 10.1016/j.annemergmed.2006.06.039.

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

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Free PMC article
Comparative Study

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

Alexandra Mardimae et al. Ann Emerg Med. .
Free PMC article

Abstract

Study objective: In a pandemic, hypoxic patients will require an effective oxygen (O2) 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 O2 supplementation while maintaining respiratory isolation.

Methods: An N95 mask was modified to deliver O2 by inserting a plastic manifold consisting of a 1-way inspiratory valve, an O2 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 O2 (F(I)O2) delivered by the N95 O2 mask, the Hi-Ox80 O2 mask, and the nonrebreathing mask during resting ventilation and hyperventilation, each at 3 O2 flow rates; (2) the ability of the N95 mask, the N95 O2 mask, and the nonrebreathing mask to filter microparticles from ambient air; and (3) to contain microparticles generated inside the mask.

Results: The F(I)O2s (median [range]) delivered by the Hi-Ox80 O2 mask, the N95 O2 mask, and the nonrebreathing mask during resting ventilation, at 8 L/minute O2 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 FiO2s of all 3 masks were clinically equivalent. The N95 O2 mask, but not the nonrebreathing mask, provided the same efficiency of filtration of internal and external particles as the original N95, regardless of O2 flow into the mask.

Conclusion: An N95 mask can be modified to administer a clinically equivalent FiO2 to a nonrebreathing mask while maintaining its filtration and isolation capabilities.

Figures

Figure E1
Figure E1
A, Modified Hi-Ox80 mask. B, N95 O2 mask. C, Nonrebreathing mask.
Figure 1
Figure 1
Schematic of an N95 mask modified by the addition of an oxygen manifold consisting of a 1-way inspiratory valve, an oxygen inlet and an oxygen reservoir.
Figure 2
Figure 2
Particle testing setup. The N95 oxygen mask contains an internal gas sampling port and a separate port used for microparticle infusion.
Figure 3
Figure 3
Median inspired fractional concentrations of oxygen (FiO2) under all experimental conditions. Bar extensions show range of data.
Figure 4
Figure 4
Protective function. Internal particle concentrations expressed as a percentage of external concentrations. Median values for the N95 mask and the N95 O2 mask at 2 and 10 L/min of O2 flow were all <1%. Median values for the nonrebreathing mask at 2 and 10 L/min of O2 flow were 53% and 17%, respectively. The boxes outline the 25th and 75th percentiles, the bars indicate the 10th and 90th percentiles, and the dots indicate the outlying values. For quantitative data regarding the protection function of each mask, see Table E1 (available online at http://www.annemergmed.com).
Figure 5
Figure 5
A, Isolation function at 6 cm. External particle concentrations measured at 6 cm from the mask, expressed as a percentage of change from background concentrations. Median values for the N95 mask and the N95 O2 mask at 2 and 10 L/min of O2 flow were indistinguishable from one another. Median values for the nonrebreathing mask at 2 and 10 L/min of O2 flow were 800% and 330%, respectively. The boxes outline the 25th and 75th percentiles, the bars indicate the 10th and 90th percentiles, and the dots indicate the outlying values. B, Isolation function at 50 cm. External particle concentrations measured at 50 cm from the mask, expressed as a percentage of change from background concentrations. Median values for the N95 mask and the N95 O2 mask at 2 and 10 L/min of O2 flow were indistinguishable from one another. Median values for the nonrebreathing mask at 2 and 10 L/min of O2 flow were 450% and 95%, respectively. The boxes outline the 25th and 75th percentiles, the bars indicate the 10th and 90th percentiles, and the dots indicate the outlying values. For quantitative data regarding the isolation function of each mask, see Table E2, Table E3 (available online at http://www.annemergmed.com). NRM, Nonbreathing mask.

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