With the COVID-19 pandemic underway, clinicians have been raising concerns about aerosol generating procedures (AGPs) in the course of patient treatment. Because the disease spreads via droplets , AGPs could expose healthcare workers to a greater risk of nosocomial transmission.
Should We Avoid AGPs?
A recent Lancet Respiratory Medicine Correspondence by Cheung et al., concluded the following:
“An experiment with a mannikin showed that NIV or HFNC, when well applied with an optimal fit, only lead to minimal dispersion of exhaled air. However, the specific NIV and HFNC models and modes tested in the study are not universally used across all hospitals. Therefore, to avoid confusion and potential harm, we do not recommend using NIV or HFNC until the patient is cleared of COVID-19….We recommend that endotracheal intubation is done by an expert specialised in the procedure.”
While this correspondence calls for intubation, it itself makes it clear that there is evidence for minimal aerosol generation when using noninvasive ventilation or high flow modalities.
What Do Medical And Health Organization Guidelines Recommend?
Both the Center of Disease Control and Prevention (CDC) and the World Health Organization (WHO) list NIV and HFNC/high velocity therapy among treatment options for COVID-19 cases. They also recommend precautions be taken, such as use of appropriate PPEs (like a N-95 respirator and gloves, among others).
According to WHO’s Clinical Management Guidelines: “Recent publications suggest that newer HFNO and NIV systems with good interface fitting do not create widespread dispersion of exhaled air and therefore should be associated with low risk of airborne transmissions”.   
The Society of Critical Care Medicine (SCCM) specifically recommends high flow oxygen as a front-line therapy over the use of NiPPV for patients not requiring intubation. Their guidelines state: “patients may find HFNC more comfortable than NIPPV. Given the evidence for a decreased risk of intubation with HFNC compared with NIPPV in acute hypoxemic respiratory failure and studies suggesting that NIPPV may carry a greater risk of nosocomial infection of healthcare providers, we suggest HFNC over NIPPV.” 
Additionally, recent computational fluid dynamics modeling studies show that it’s possible to substantially reduce particulate dispersion with high velocity therapy through the use of a simple surgical mask.
Not All AGPs Are The Same
All respiratory support interventions are AGPs. The act of changing the airway or its function in some way has the risk of generating potentially infectious droplets. However, not all AGPs present the same level of risk.
In a systematic review of the transmission risk of acute respiratory infections from aerosol generating procedures, Tran and colleagues found that the risk of transmission for high flow was not significant, when compared to significant increased risk associated with tracheal intubation, non-invasive positive pressure ventilation, tracheostomy, and manual ventilation.  Table 1 shows some select findings from Tran et al.’s meta-analysis.Table 1: Aerosol Procedures as Risk Factors of SARS Transmission. Adapted from Tran K et al. View original full table here.
It becomes clear, that high flow oxygen may have a lower risk of SARS transmission than any of the procedures associated with intubation.
High velocity therapy, NIV, and high flow are recommended tools for the management of COVID-19 symptoms. Healthcare workers should be aware which AGPs present a greater risk for nosocomial infection and should take proper precautions. An additional consideration could be weighing the advantages of each modality in addressing most concerns in one. For example, high velocity therapy has a low transmission risk, and can provide oxygenation and mask-free ventilatory support for spontaneously breathing patients.
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 Report of the WHO-China Joint Mission on Coronavirus Disease 2019 (COVID-19). 2020.
 Cheung JC, Ho LT, Cheng JV, Cham EYK, Lam KN. Staff safety during emergency airway management for COVID-19 in Hong Kong. Lancet Respir Med. 2020.
 Clinical management of severe acute respiratory infection when novel coronavirus (2019-nCoV) infection is suspected: Interim Guide, Page 6 March 13 2020
 Leung CCH, Joynt GM, Gomersall CD, et al. Comparison of high-flow nasal canula versus oxygen face mask for environmental bacterial pneumonia patients, a randomized controlled crossover trial. J Hosp Infect 2019: 101:84-87.
 Hui DS, Chow BK, Lo T, et al. Exhaled air dispersion during high-flow nasal cannula therapy versus CPAP via different masks, Eur Respir J 2019,53.
 Hui DS, Chow BK, Lo T, et al, Exhaled air dispersion during noninvasive via helmets and total facemask. Chest 2015: 147:1336-43.
 Alhazzani, W. et al. Surviving Sepsis Campaign: Guidelines on the Management of Critically Ill Adults with Coronavirus Disease 2019 (COVID-19). First published March 2020 on https://www.sccm.org/disaster. Last accessed March 23, 2020.
 Tran K, Cimon K, Severn M, Pessoa-Silva CL, Conly J (2012) Aerosol Generating Procedures and Risk of Transmission of Acute Respiratory Infections to Healthcare Workers: A Systematic Review. PLoS ONE 7(4): e35797. doi:10.1371/journal.pone.0035797