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Original research
Aerosol emission from the respiratory tract: an analysis of aerosol generation from oxygen delivery systems
  1. Fergus W Hamilton1,2,
  2. Florence K A Gregson3,
  3. David T Arnold4,
  4. Sadiyah Sheikh3,
  5. Kirsty Ward5,
  6. Jules Brown6,
  7. Ed Moran7,
  8. Carrie White8,
  9. Anna J Morley4,
  10. AERATOR Group,
  11. Bryan R Bzdek3,
  12. Jonathan P Reid3,
  13. Nicholas A Maskell4,
  14. James William Dodd2,4
    1. 1 Infection Science, North Bristol NHS Trust, Westbury on Trym, UK
    2. 2 MRC Integrative Epidemiology Unit, Bristol, UK
    3. 3 Bristol Aerosol Research Centre, School of Chemistry, University of Bristol, Bristol, UK
    4. 4 Academic Respiratory Unit, North Bristol NHS Trust, Westbury on Trym, UK
    5. 5 Physiotherapy Department, North Bristol NHS Trust, Westbury on Trym, UK
    6. 6 Anaesthetics and Intensive Care Department, North Bristol NHS Trust, Westbury on Trym, UK
    7. 7 Infectious Diseases, North Bristol NHS Trust, Bristol, UK
    8. 8 Research and Development, North Bristol NHS Trust, Westbury on Trym, UK
    1. Correspondence to Dr Fergus W Hamilton, MRC-IEY, University of Bristol, Bristol BS10 5NB, UK; fergus.hamilton{at}bristol.ac.uk

    Abstract

    Introduction continuous positive airway pressure (CPAP) and high-flow nasal oxygen (HFNO) provide enhanced oxygen delivery and respiratory support for patients with severe COVID-19. CPAP and HFNO are currently designated as aerosol-generating procedures despite limited high-quality experimental data. We aimed to characterise aerosol emission from HFNO and CPAP and compare with breathing, speaking and coughing.

    Materials and methods Healthy volunteers were recruited to breathe, speak and cough in ultra-clean, laminar flow theatres followed by using CPAP and HFNO. Aerosol emission was measured using two discrete methodologies, simultaneously. Hospitalised patients with COVID-19 had cough recorded using the same methodology on the infectious diseases ward.

    Results In healthy volunteers (n=25 subjects; 531 measures), CPAP (with exhalation port filter) produced less aerosol than breathing, speaking and coughing (even with large >50 L/min face mask leaks). Coughing was associated with the highest aerosol emissions of any recorded activity. HFNO was associated with aerosol emission, however, this was from the machine. Generated particles were small (<1 µm), passing from the machine through the patient and to the detector without coalescence with respiratory aerosol, thereby unlikely to carry viral particles. More aerosol was generated in cough from patients with COVID-19 (n=8) than volunteers.

    Conclusions In healthy volunteers, standard non-humidified CPAP is associated with less aerosol emission than breathing, speaking or coughing. Aerosol emission from the respiratory tract does not appear to be increased by HFNO. Although direct comparisons are complex, cough appears to be the main aerosol-generating risk out of all measured activities.

    • non invasive ventilation
    • infection control
    • respiratory infection
    • viral infection

    Data availability statement

    All data relevant to the study are included in the article or uploaded as supplemental information. Anonymised aerosol data from the AERATOR Study will be submitted to the Bristol data repository (data.bris.ac.uk) on completion of the full study.

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    Data availability statement

    All data relevant to the study are included in the article or uploaded as supplemental information. Anonymised aerosol data from the AERATOR Study will be submitted to the Bristol data repository (data.bris.ac.uk) on completion of the full study.

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    Footnotes

    • Twitter @gushamilton, @theotherdodd

    • FWH and FKAG contributed equally.

    • NAM and JWD contributed equally.

    • Collaborators The AERATOR group: Arnold D; Brown J; Bzdek BR; Davidson A; Dodd JW; Gormley M; Gregson F; Hamilton F; Maskell N; Murray J; Keller J; Pickering AE; Reid J; Sheikh S; Shrimpton A.

    • Contributors NAM, JWD, FWH, FKAG, DTA and JB designed the experiments. SS and FKAG analysed the data, with BRB and JPR providing supervisory support and analysis. EM coordinated inpatients with COVID-19, CW and AJM coordinated the study. KW provided expert opinion and analysis on respiratory support. JWD is the guarantor.

    • Funding NIHR-UKRI Rapid COVID Rolling Call (Ref: COV003). JWD’s time was funded by MRC CARP Fellowship. (MR/T005114/1); FWH’s time was funded by a GW4-CAT Wellcome Doctoral Fellowship; BRB’s time was funded by an NERC grant (NE/P018459/1).

    • Competing interests None declared.

    • Provenance and peer review Not commissioned; externally peer reviewed.

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