A pilot study of near-field airborne particle concentrations in young children undergoing high flow nasal cannula therapy.

Gall, Elliott T; Laguerre, Aurélie; Noelck, Michelle; Van Meurs, Annalise; Austin, Jared A; Foster, Byron A

BACKGROUND High flow nasal cannula therapy (HFNC) may increase aerosol generation, putting healthcare workers at risk, including from SARS-CoV-2. AIM This study examined whether use of HFNC increases near-field aerosols and if there is a relationship 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 one within 0.5 m, station two at 2 m, and station three on the other side of the room. We measured carbon dioxide (CO2) and relative humidity. Far-field measurements were used to adjust the near-field measurements. FINDINGS We enrolled ten children ranging from 6-23 months (median 9 months). Elevated CO2 indicated the near-field measurements were in the breathing plane. Near-field breathing plane concentrations of aerosols with diameter 0.3 - 10 μm are elevated by the presence of the patient with no HFNC flow, relative to the room far-field, by 0.45 #/cm3. While we observed variability between subjects in their emission and dispersion of particles, we did not find an association between HFNC use, at any flowrate, 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 0.3-10 μm and CO2 were not affected by the use of HFNC.