Near-field airborne particle concentrations in young children undergoing high-flow nasal cannula therapy: a pilot study

Background: High-flow nasal cannula therapy (HFNC) may increase aerosol generation, putting healthcare workers at risk, including from SARS-CoV-2. Aim: To examine whether use of HFNC increases near-field aerosols and whether there is an association with flow rate. Methods: Subjects aged four weeks to 24 months were recruited. Each child received HFNC therapy at different flow rates. Three stations with particle counters were deployed to measure particle concentrations and dispersion in the room: station 1 within 0.5 m, station 2 at 2 m, and station 3 on the other side of the room. Carbon dioxide (CO₂) and relative humidity were measured. Far-field measurements were used to adjust the near-field measurements. Findings: Ten children were enrolled, aged from 6 to 24 months (median: 9). Elevated CO₂ indicated that the near-field measurements were in the breathing plane. Near-field breathing plane concentrations of aerosols with diameter 0.3–10 μm were elevated by the presence of the patient with no HFNC flow, relative to the room far-field, by 0.45 particles/cm³. Whereas variability between subjects in their emission and dispersion of particles was observed, no association was found between HFNC use, at any flow rate, and near-field particle counts. Conclusion: This method of particle sampling is feasible in hospital settings; correcting the near-patient aerosol and CO₂ levels for the room far-field may provide proxies of exposure risk to pathogens generated. In this pilot, near-patient levels of particles with a diameter between 0.3 and 10 μm and CO₂ were not affected by the use of HFNC.