Aerosol emission from the respiratory tract: an analysis of aerosol generation from oxygen delivery systems
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Abstract
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.
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SciScore for 10.1101/2021.01.29.21250552: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement IRB: Ethical approval was given by the North West Research Ethics Committee (Ref: 20/NW/0393, HRA Approved Randomization not detected. Blinding not detected. Power Analysis not detected. Sex as a biological variable not detected. Table 2: Resources
Software and Algorithms Sentences Resources 0 (TSI Incorporated, Shoreview, NM, USA) and Microsoft Excel. Microsoft Excelsuggested: (Microsoft Excel, RRID:SCR_016137)A custom-written software in LabVIEW (National Instruments, Texas, USA) was used to automate the analysis process for increased efficiency. LabVIEWsuggested: (LabView , RRID:SCR_014325)Results from OddPub: We did not detect open data. We also did not detect open code. …
SciScore for 10.1101/2021.01.29.21250552: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement IRB: Ethical approval was given by the North West Research Ethics Committee (Ref: 20/NW/0393, HRA Approved Randomization not detected. Blinding not detected. Power Analysis not detected. Sex as a biological variable not detected. Table 2: Resources
Software and Algorithms Sentences Resources 0 (TSI Incorporated, Shoreview, NM, USA) and Microsoft Excel. Microsoft Excelsuggested: (Microsoft Excel, RRID:SCR_016137)A custom-written software in LabVIEW (National Instruments, Texas, USA) was used to automate the analysis process for increased efficiency. LabVIEWsuggested: (LabView , RRID:SCR_014325)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:Strengths and weaknesses: Comparisons with previous literature: There are few previous published studies of aerosol generation from oxygen delivery systems and respiratory support. Hui and colleagues performed experiments on CPAP, HFNO and simple nasal cannulae using smoke inside a human patient simulator and measured the distance and trajectory of the smoke. 13,26 As commented by others, 12 unsurprisingly the higher pressure forced the smoke longer distances, through small ports in masks. The most similar, recent study was performed by Gaeckle et al.12 In this study, measurements of the aerodynamic number concentration (by APS) were reported from ten healthy volunteers in a negative pressure room (∼15 air exchanges per hour), with an additional portable HEPA filter added to reduce background aerosol concentration. A similar protocol was used to ours, although they measured simple nasal cannulae and changes in respiration. Importantly, they reported a background aerosol concentration of ∼0.060 particles/cm3 (compared to zero under laminar flow), larger than we report for many activities (including breathing and speaking with a facemask). As well as a high background, the aerosol number concentration was highly variable in their study (see Figure 4 and E3 from reference 11, and figure 3 here for comparison). This variability makes reporting accurate aerosol concentrations for short events (e.g. a cough) challenging, as we noted in recruiting our COVID-19 patients. Consistent w...
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.
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