TY - JOUR T1 - High-flow nasal cannula for COVID-19 patients: risk of bio-aerosol dispersion JF - European Respiratory Journal JO - Eur Respir J DO - 10.1183/13993003.03136-2020 VL - 56 IS - 4 SP - 2003136 AU - Jie Li AU - James B. Fink AU - Stephan Ehrmann Y1 - 2020/10/01 UR - http://erj.ersjournals.com/content/56/4/2003136.abstract N2 - We appreciate the comments of J. Elshof and co-workers on our article “High-flow nasal cannula for COVID-19 patients: low risk of bio-aerosol dispersion” [1] and agree that further research is warranted to reduce the risk of virus transmission from infected patients. The presented in vitro data of J. Elshof and co-workers from a model using light detection of smoke dispersion distance and velocity, suggesting that high-flow nasal cannula (HFNC) generates a larger dispersion distance than non-rebreather masks and Venturi masks, is in contrast to reports from Hui et al. [2] using a similar model. Presumably, because the smoke used by J. Elshof and co-workers was larger (0.3–2.5 µm) than that used by Hui et al. [2] (≤1 µm), the larger particles dispersed differently. It should be noted that smoke in both models represents only a small fraction of the range of bio-aerosols generated by patients during breathing, speaking, coughing or sneezing [3]. Using the same size airway model, J. Elshof and co-workers observed that the dispersion distance decreased from 71 cm to 25 cm by changing the nasal cannula size from small to large when HFNC flow was set at 30 L·min−1; however, when HFNC flow was set at 60 L·min−1, the medium-size nasal cannula generated a shorter distance than both small and large nasal cannulas. This raises the role of proper fit of prongs to nares and highlights the limitations of modelling. Regardless of the sizes of nasal cannula, the dispersion distance was farther with 60 L·min−1 than 30 L·min−1, which is in line with the results of Hui et al. [2] and may be expected, as higher velocity of the gas will carry exhaled smoke to a further distance. However, this effect of total flow did not occur when testing the Venturi mask. Surprisingly, the Venturi mask with large open holes and a total gas flow of 40 L·min−1 generated a shorter dispersion distance than normal breathing. These inconsistencies are difficult to interpret without comprehensive peer review of extensive methods and results. Whether smoke imaging models truly reflect the natural features of the transportation and dispersion of bio-aerosols generated by patients has not been established and results from these studies should be interpreted cautiously.High-flow nasal cannula does not generate higher risk of bio-aerosol dispersion than conventional oxygen masks https://bit.ly/2Yn0RQn ER -