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High-flow nasal cannula for COVID-19 patients: risk of bio-aerosol dispersion

Jie Li, James B. Fink, Stephan Ehrmann
European Respiratory Journal 2020 56: 2003136; DOI: 10.1183/13993003.03136-2020
Jie Li
1Dept of Cardiopulmonary Sciences, Division of Respiratory Care, Rush University Medical Center, Chicago, IL, USA
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James B. Fink
1Dept of Cardiopulmonary Sciences, Division of Respiratory Care, Rush University Medical Center, Chicago, IL, USA
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Stephan Ehrmann
2CHRU Tours, Médecine Intensive Réanimation, CIC INSERM 1415, CRICS-TriggerSep network, Tours, France
3INSERM, Centre d’étude des pathologies respiratoires, U1100, Université de Tours, Tours, France
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Abstract

High-flow nasal cannula does not generate higher risk of bio-aerosol dispersion than conventional oxygen masks https://bit.ly/2Yn0RQn

From the authors:

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.

In a recent clinical study of aerosol particle concentrations and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus detection in the vicinity of patients with coronavirus disease 2019 (COVID-19), aerosol particle size and concentrations were measured before and after HFNC was applied to patients. No difference was observed between conventional nasal cannula applied prior to HFNC, and HFNC. More importantly, no SARS-CoV-2 virus was detected in the room air with the sampling cassette placed at 30 cm from the patients’ airways for an hour (unpublished data).

It should also be noted that oxygen masks, including Venturi masks, non-rebreather masks, simple masks and aerosol masks, do not enable placement of a filter, except for some oxygen masks with special design [3, 4]. Bio-aerosols generated by patients might be exhaled via the holes or the one-way valve on the masks, and the high gas flow from the masks helps carry those bio-aerosols to a further distance. In contrast, patients using HFNC can wear a surgical mask over the HFNC, in order to reduce the dispersion of bio-aerosols that they generate [4, 5].

In all, compared to conventional oxygen devices, HFNC has been proven to improve oxygenation and reduce intubation rate in hypoxaemic patients [6]. Abandoning HFNC to use other oxygen devices for the uncertain risks of virus transmission is unnecessary and ill advised. Special caution taken to protect personnel during “aerosol-generating procedures” is more important than avoidance of “aerosol-dispersing procedures” [3]. Studying the production of aerosols by breathing support devices using laboratory models (e.g. smoke dispersion) is interesting but has important limitations, because they are just simulations. What is really important, and still lacking in the literature, is a real-life study assessing the actual virus cargo within the patient's generated aerosols and, more importantly, how infective such a viral cargo is, which would probably depend on the physical and chemical characteristics of the aerosol particles.

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Footnotes

  • Author contributions: J. Li conceived of the idea and drafted the manuscript. J.B. Fink and S. Ehrmann provided critical revision on the manuscript. All authors reviewed and revised the manuscript and approved the final draft.

  • Conflict of interest: J. Li reports grants from Fisher and Paykel Healthcare Ltd, during the conduct of the study, and grants from the Rice Foundation, outside the submitted work.

  • Conflict of interest: J.B. Fink is the Chief Science Officer of Aerogen Pharma Corp.

  • Conflict of interest: S. Ehrmann reports grants, personal fees and non-financial support from Fisher and Paykel, during the conduct of the study, as well as grants, personal fees and non-financial support from Aerogen Ltd, personal fees and non-financial support from La diffusion technique française, and grants from Hamilton medical, outside the submitted work.

  • Received August 13, 2020.
  • Accepted August 17, 2020.
  • Copyright ©ERS 2020
http://creativecommons.org/licenses/by-nc/4.0/

This version is distributed under the terms of the Creative Commons Attribution Non-Commercial Licence 4.0.

References

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    1. Li J,
    2. Fink JB,
    3. Ehrmann S
    . High-flow nasal cannula for COVID-19 patients: low risk of bio-aerosol dispersion. Eur Respir J 2020; 55: 2000892. doi:10.1183/13993003.00892-2020
    OpenUrlAbstract/FREE Full Text
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    1. Hui DS,
    2. Chow BK,
    3. Lo T, et al.
    Exhaled air dispersion during high-flow nasal cannula therapy versus CPAP via different masks. Eur Respir J 2019; 53: 1802339. doi:10.1183/13993003.02339-2018
    OpenUrlAbstract/FREE Full Text
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    1. Dhand R,
    2. Li J
    . Coughs and sneezes: their role in transmission of respiratory viral infections, including SARS-CoV-2. Am J Respir Crit Care Med 2020; 202: 651–659. doi:10.1164/rccm.202004-1263PP
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    1. Kaur R,
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    Practical strategies to reduce nosocomial transmission to healthcare professionals providing respiratory care to patients with COVID-19. Crit Care 2020; in press [https://doi.org/10.1186/s13054-020-03231-8].
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    1. Leonard S,
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    3. Walsh BK, et al.
    Preliminary findings on control of dispersion of aerosols and droplets during high-velocity nasal insufflation therapy using a simple surgical mask: implications for the high-flow nasal cannula. Chest 2020; 158: 1046–1049. doi:10.1016/j.chest.2020.03.043
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    1. Li J,
    2. Jing G,
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    . Year in review 2019: high-flow nasal cannula oxygen therapy for adult subjects. Respir Care 2020; 65: 545–557. doi:10.4187/respcare.07663
    OpenUrlAbstract/FREE Full Text
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High-flow nasal cannula for COVID-19 patients: risk of bio-aerosol dispersion
Jie Li, James B. Fink, Stephan Ehrmann
European Respiratory Journal Oct 2020, 56 (4) 2003136; DOI: 10.1183/13993003.03136-2020

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High-flow nasal cannula for COVID-19 patients: risk of bio-aerosol dispersion
Jie Li, James B. Fink, Stephan Ehrmann
European Respiratory Journal Oct 2020, 56 (4) 2003136; DOI: 10.1183/13993003.03136-2020
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