Aerosol Generation from the Respiratory Tract with Various Modes of Oxygen Delivery

Abstract

Rationale: Aerosol generation with modes of oxygen therapy such as high-flow nasal cannula and noninvasive positive-pressure ventilation is a concern for healthcare workers during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. The amount of aerosol generation from the respiratory tract with these various oxygen modalities is unknown.Objectives: To measure the size and number concentration of particles and droplets generated from the respiratory tract of humans exposed to various oxygen delivery modalities.Methods: Ten healthy participants with no active pulmonary disease were enrolled. Oxygen modalities tested included nonhumidified nasal cannula, face mask, heated and humidified high-flow nasal cannula, and noninvasive positive-pressure ventilation. Aerosol generation was measured with each oxygen mode while participants performed maneuvers of normal breathing, talking, deep breathing, and coughing. Testing was conducted in a negative-pressure room. Particles with a diameter between 0.37 and 20 μm were measured using an aerodynamic particle spectrometer.Measurements and Main Results: Median particle concentration ranged from 0.041 to 0.168 particles/cm³. Median diameter ranged from 1.01 to 1.53 μm. Cough significantly increased the number of particles measured. Measured aerosol concentration did not significantly increase with the use of either humidified high-flow nasal cannula or noninvasive positive-pressure ventilation. This was the case during normal breathing, talking, deep breathing, and coughing.Conclusions: Oxygen delivery modalities of humidified high-flow nasal cannula and noninvasive positive-pressure ventilation do not increase aerosol generation from the respiratory tract in healthy human participants with no active pulmonary disease measured in a negative-pressure room.

Keywords: SARS-CoV-2; droplet; particle.

Figure 1.

Particle number concentration with various modes of oxygen delivery. Box-and-whisker plots demonstrate the median and interquartile ranges. Note the change in scale of the y-axis in coughing. The horizontal dashed line represents the average baseline particle number concentration of the room (0.060 particles/cm³). FM = face mask; HFNC = heated and humidified high-flow nasal cannula; NC = nasal cannula; NIPPV = noninvasive positive-pressure ventilation.

Figure 2.

Geometric mean diameter of particles with different modes of oxygen delivery. Box-and-whisker plots demonstrate the median and interquartile ranges. The horizontal dashed line represents the average geometric mean diameter of the particles in the baseline measurements of the room (1.80 μm). For definition of abbreviations, see Figure 1.

Figure 3.

Particle concentration (aerodynamic diameter 0.52–20 μm) exhaled from the respiratory tract during coughing, deep breathing, normal breathing, and talking and divided into particles with an aerodynamic diameter greater than 1 μm (top chart) and less than 1 μm (bottom chart). There appears to be a difference in the number and diameter of particles with different respiratory maneuvers, when stratified by particle size. Coughing and deep breathing appear to generate a larger number of particles less than 1 μm than normal breathing or talking. FM = 15 L/min face mask; HNC 10 = humidified high-flow nasal cannula 10 L/min; HNC 30 = humidified high-flow nasal cannula 30 L/min; HNC 50 = humidified high-flow nasal cannula 50 L/min; NC = 4 L/min nasal cannula; NV 12/5 = noninvasive positive-pressure ventilation 12/5; NV 20/10 = noninvasive positive pressure ventilation 20/10; P1–P10 = participants 1–10; RA = room air.

Figure 4.

Representative samples of three participants (P5, P7, and P8). Particle number concentration exhaled over time on a logarithmic scale with the various oxygen modalities and respiratory maneuvers are shown. White colored rectangles denote background room measurements. C = coughing; D = deep breathing; FM = face mask; HFNC = heated and humidified high-flow nasal cannula; N = normal breathing; NC = nasal cannula; NIPPV = noninvasive positive-pressure ventilation; T = talking.