Assessment of dispersion of airborne particles of oral/nasal fluid by high flow nasal cannula therapy

  1. M. C. Jermy
  2. C. J. T. Spence
  3. R. Kirton
  4. J. F. O’Donnell
  5. N. Kabaliuk
  6. S. Gaw
  7. H. Hockey
  8. Y. Jiang
  9. Z. Zulkhairi Abidin
  10. R. L. Dougherty
  11. P. Rowe
  12. A. S. Mahaliyana
  13. A. Gibbs
  14. S. A. Roberts

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Abstract

Nasal High Flow (NHF) therapy delivers flows of heated humidified gases up to 60 LPM (litres per minute) via a nasal cannula. Particles of oral/nasal fluid released by patients undergoing NHF therapy may pose a cross-infection risk, which is a potential concern for treating COVID-19 patients.

Methods

Liquid particles within the exhaled breath of healthy participants were measured with two protocols: (1) high speed camera imaging and counting exhaled particles under high magnification (6 participants) and (2) measuring the deposition of a chemical marker (riboflavin-5-monophosphate) at a distance of 100 and 500 mm on filter papers through which air was drawn (10 participants). The filter papers were assayed with HPLC. Breathing conditions tested included quiet (resting) breathing and vigorous breathing (which here means nasal snorting, voluntary coughing and voluntary sneezing). Unsupported (natural) breathing and NHF at 30 and 60 LPM were compared.

Results

  • Imaging: During quiet breathing, no particles were recorded with unsupported breathing or 30 LPM NHF (detection limit for single particles 33 μm). Particles were detected from 2 of 6 participants at 60 LPM quiet breathing at approximately 10% of the rate caused by unsupported vigorous breathing. Unsupported vigorous breathing released the greatest numbers of particles. Vigorous breathing with NHF at 60 LPM, released half the number of particles compared to vigorous breathing without NHF.

  • Chemical marker tests: No oral/nasal fluid was detected in quiet breathing without NHF (detection limit 0.28 μL/m 3 ). In quiet breathing with NHF at 60 LPM, small quantities were detected in 4 out of 29 quiet breathing tests, not exceeding 17 μL/m 3 . Vigorous breathing released 200–1000 times more fluid than the quiet breathing with NHF. The quantities detected in vigorous breathing were similar whether using NHF or not.

    • Conclusion

    During quiet breathing, 60 LPM NHF therapy may cause oral/nasal fluid to be released as particles, at levels of tens of μL per cubic metre of air. Vigorous breathing (snort, cough or sneeze) releases 200 to 1000 times more oral/nasal fluid than quiet breathing (p < 0.001 with both imaging and chemical marker methods). During vigorous breathing, 60 LPM NHF therapy caused no statistically significant difference in the quantity of oral/nasal fluid released compared to unsupported breathing. NHF use does not increase the risk of dispersing infectious aerosols above the risk of unsupported vigorous breathing. Standard infection prevention and control measures should apply when dealing with a patient who has an acute respiratory infection, independent of which, if any, respiratory support is being used.

    Clinical trial registration

    ACTRN12614000924651

    Article activity feed

    1. Version published to 10.1371/journal.pone.0246123
    2. ScreenIT

      SciScore for 10.1101/2020.05.14.20102517: (What is this?)

      Please note, not all rigor criteria are appropriate for all manuscripts.

      Table 1: Rigor

      Institutional Review Board Statementnot detected.
      Randomizationnot detected.
      Blindingnot detected.
      Power Analysisnot detected.
      Sex as a biological variablenot detected.

      Table 2: Resources

      No key resources detected.

      Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

      Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
      This study had numerous limitations: all participants were healthy; there was a narrow age distribution (although previous research indicates no reason to expect different results from other participants. Tobin et al. (1983), for example, measured the breathing patterns of 65 healthy participants from 20 to 81 years of age and found no effect of age on the mean values of various breathing pattern components); all participants were in a sitting position and a supine position may give different results; the imaging could not detect particles of less than 33 microns in diameter; the chemical marker could not discriminate on particle size, and due to the limited physical size of the filter paper, might not collect all of the discharge plume. In both methods, some of the sample fluid used to moisten the mucosa was swallowed. In both methods the instilled fluid was either saline or water and as such, be more easily atomized and/or produce smaller diameter particles. There was considerable variability in the results. It is speculated that this large variability is due to a range of factors including: some of the 1 ml sample going down the throat pre-measurement, and the variability of simulated snorting, coughing and sneezing.

      Results from TrialIdentifier: No clinical trial numbers were referenced.

      Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

      Results from JetFighter: We did not find any issues relating to colormaps.

      Results from rtransparent:
      • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
      • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
      • No protocol registration statement was detected.

      About SciScore

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    3. Version published to 10.1101/2020.05.14.20102517v2 on medRxiv
    4. Version published to 10.1101/2020.05.14.20102517v1 on medRxiv