DOM COVID-19 Journal Club: Variation in Aerosol Production Across Oxygen Delivery Devices in Spontaneously Breathing Human Subjects

Background: Due to theoretical concerns that heated high-flow nasal cannula (HHFNC, e.g. Optiflow, Vapotherm, Airvo) may increase aerosolization of SARS-CoV-2, and therefore increase risk of transmission to healthcare workers, several hospital systems and authorities have recommended against its use in COVID-19. HHFNC has previously been shown to decrease the need for mechanical ventilation and improve mortality in acute hypoxemic respiratory failure. 2,3

Methods: Healthy volunteers (4) were placed in simulated medical rooms while wearing 6L nasal cannula (NC), non-rebreather masks (NRB), and HHFNC with 30L/min and 60L/min flow rates.3 Aerosol measurements were obtained using scanning mobility particle sizing systems and particle counters, capable of assessing particles ranging from 10 to 10,000 nm, the relevant range for human coughing. Background aerosol measurements were obtained, as well as with the participants wearing the supplemental oxygen devices, and with spontaneous and intentional coughing.

Results: There was no variation in aerosol level within patients breathing room air, 6L/min NC, 15L/min NRB, 30L/min HHFNC, and 60L/min HHFNC, regardless of coughing.

Limitations: Very small study, healthy volunteers without active viral infection or shedding, limited time of observation (10 minutes).

Conclusions: The initial hesitation to use HHFNC in COVID-19 was based on theory, not data, and the practice of “early intubation” is potentially harmful to patients 4. This small study suggests that HHFNC may not, in fact, increase aerosolization of particles. Given the robust evidence and experience with HHFNC in patients with acute hypoxemic respiratory failure, these devices are likely to improve outcomes in patients with COVID-19, and should be used when indicated.


  1. Iwashyna T, et al. Variation in Aerosol Production Across Oxygen Delivery Devices in Spontaneously Breathing Human Subjects. medRxiv 2020.04.15.20066688.
  2. Frat, J.-P., et al. High-Flow Oxygen through Nasal Cannula in Acute Hypoxemic Respiratory Failure. New England Journal of Medicine (2015) 372(23): 2185-2196.
  3. Hernandez G, et al. Effect of Postextubation High-Flow Nasal Cannula vs Noninvasive Ventilation on Reintubation and Postextubation Respiratory Failure in High-Risk Patients: A Randomized Clinical Trial. JAMA. 172 2016;316(15):1565-1574.
  4. Goyal P, et al. Clinical Characteristics of Covid-19 in New York City. New England Journal of. 2020 Apr 17. doi: 10.1056/NEJMc2010419. 

The Department of Medicine COVID-19 Journal Club is dedicated to understand and applying data on COVID-19 to inform prevention and management efforts for healthcare workers and patients

This article by Stephen Halliday MD, MSCI, assistant professor, Allergy, Pulmonary and Critical Care Medicine.