Aerosol emission from the respiratory tract: an analysis of aerosol generation from oxygen delivery systems

Abstract

Introductioncontinuous 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 methodsHealthy 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.ResultsIn 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.ConclusionsIn 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.

Aerosol generation during general anesthesia is comparable to coughing: An observational clinical study

“…[19][20][21] A paradigm shift is currently under discussion: to justify the use of a higher level of PPE in AGP classified medical procedure compared to normal patient contact, the AGP should generate aerosol concentrations that are higher than in normal patient care where caregivers are constantly exposed for the particles generated by breathing, speaking, and coughing. 22 As coughing is known to generate higher aerosol amounts than other regular respiratory activities, 23 we considered it similarly to previous statements as a justified benchmark that generates an upperlimit for everyday clinical aerosol exposure.…”

A quantitative evaluation of aerosol generation from upper airway suctioning during tracheal intubation and extubation sequences

“…Procedures' or better even to reassess use of the term at all [11]. This term places the emphasis of risk on the medical procedure (many of which have been demonstrated not to generate aerosol [6,[16][17][18][19]) whilst neglecting multiple factors that should be considered during the risk of assessment of any patient interaction. The risk assessment should consider the likelihood of the patient being infected with a respiratory pathogen (such as SARS-CoV-2), the proximity of the operator to the patient's respiratory tract, the duration of this proximity, the health, immune and vaccination status of the operator and the environment in which the interaction occurs.…”

Source terms for benchmarking models of SARS-CoV-2 transmission via aerosols and droplets

“…A recent publication showed that patients admitted to hospital with COVID-19 exhaled similar aerosol size distributions to healthy patients when breathing, speaking and coughing [ 33 ]. We also note that the studies that we have reviewed either did not mention differences in particle size distributions for male and female subjects [ 27 , 29 ], or could not find any statistically significant difference [ 28 , 31 , 32 ].…”