Quantification of aerosol dispersal from suspected aerosol-generating procedures

Abstract

Background: Oxygen-delivering modalities like humidified high-flow nasal cannula (HFNC) and noninvasive positive-pressure ventilation (NIV) are suspected of generating aerosols that may contribute to transmission of disease such as coronavirus disease 2019. We sought to assess if these modalities lead to increased aerosol dispersal compared to the use of non-humidified low-flow nasal cannula oxygen treatment (LFNC).

Methods: Aerosol dispersal from 20 healthy volunteers using HFNC, LFNC and NIV oxygen treatment was measured in a controlled chamber. We investigated effects related to coughing and using a surgical face mask in combination with the oxygen delivering modalities. An aerodynamic particle sizer measured aerosol particles (APS3321, 0.3-20 µm) directly in front of the subjects, while a mesh of smaller particle sensors (SPS30, 0.3-10 µm) was distributed in the test chamber.

Results: Non-productive coughing led to significant increases in particle dispersal close to the face when using LFNC and HFNC but not when using NIV. HFNC or NIV did not lead to a statistically significant increase in aerosol dispersal compared to LFNC. With non-productive cough in a room without air changes, there was a significant drop in particle levels between 100 cm and 180 cm from the subjects.

Conclusions: Our results indicate that using HFNC and NIV does not lead to increased aerosol dispersal compared to low-flow oxygen treatment, except in rare cases. For a subject with non-productive cough, NIV with double-limb circuit and non-vented mask may be a favourable choice to reduce the risk for aerosol spread.

FIGURE 1

a) Overview of the test chamber, sensor locations (Sensirion, SPS30: mesh sensors: A-I, three sensors at 30 cm, three at 100 cm, two at 180 cm and one at 285 cm) (TSI, APS 3321: “breathing zone single sensor”: sample point 20 cm from participant face) and other equipment. The test person was seated on a chair, with an approximate breathing zone elevation of 120 cm above the floor. The sensors were positioned 120 cm above the floor. b) Protocol structure with oxygen modalities and event elements and details. Before and between each 10-min event a 15-min period of filtering out the particles of the test chamber was performed. LFNC: low-flow nasal cannula; HFNC: high-flow nasal cannula; NIV: noninvasive positive-pressure ventilation. HF: high flow; IPAP: inspiratory positive airway pressure; EPAP: expiratory positive airway pressure

FIGURE 2

Average particles per litre of air (PPL) concentration over 10 min (red dot) between each of the eight events in each experiment, grouped according to participant (violin plots with two segment y-axes). a) Breathing-zone single sensor (particle size range 0.3–20 μm). b) average over nine mesh sensors (particle size range 0.3–10 μm). Categorical comparisons of average concentration of particles per litres of air, during the eight events of each experiment, with each red dot representing the results from 1 of 20 participants, measured by the breathing-zone single sensor (APS 3321) (c) and the average over all nine mesh sensors (d). The median is indicated with a thin black dashed line. LF: low-flow; C: cough; HF: high-flow; M: mask. e) Particle size distribution measured with the breathing-zone sensor; NIV: noninvasive positive-pressure ventilation.

FIGURE 3

Mean and median particles per litre of air, from 20 participants, for three particle size groups, measured with the breathing-zone single sensor (APS 3321), during the eight events of the experiment. The median and means show smoothed time series (moving mean with a 3-s window). The smoothing was used to increase readability and instead of a series of spikes, a smoothed square-like step response is shown for the periods with large spikes. LFNC: low-flow nasal cannula; HFNC: high-flow nasal cannula; NIV: noninvasive positive-pressure ventilation.

FIGURE 4

Mean particle concentration in particles per litre of air (y-axes) within each episode, for all mesh sensors. The particle concentration number includes particle sizes (0.3–10 μm). The placement of the plots within the graph is similar to the sensor position during the experiments, with the distance to each sensor shown in the subfigure headings. The distribution of measurements between participants is presented as violin plots, where the median is indicated with a thin black dashed line, and the quartiles with thinner dashed lines. LF: low-flow; C: cough; HF: high-flow; M: mask; NIV: noninvasive positive-pressure ventilation.