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We read with great interest the recent letter by Remy et al. regarding the use of high-flow nasal cannula (HFNC) in COVID-19 patients [1]. After reading the surviving sepsis campaign guidelines on the management of critically ill adults with coronavirus disease 2019 (COVID-19) [2], we initially shared the concern of Remy et al. regarding the recommendation to use HFNC over non-invasive positive pressure ventilation (NIPPV). However, after extensively reading the available literature, we have changed our perspective. The risk of aerosol formation and dispersion for NIPPV systems are variable depending on setting parameters and model/ mask type [3]. Viral filters can be attached to the exhalation line on most of the newer models [3]. High fidelity human model studies have demonstrated that exhaled air disperses to 40 cm with the nasal cannula and to 64 cm at 10 cm H2O inspiratory air pressure with a bilevel pressure airway pressure (BiPAP) mask [3]. That distance increased to 85 cm and > 95 cm at 18 cm H2O depending on the style of the mask used [3]. In comparison, another mannequin study of HFNC demonstrated that even at the highest setting of 60 L/min, exhaled air dispersion was 17 cm in a healthy lung scenario and only 4.8 cm in a severely diseased lung scenario [3, 4]. In other words, in terms of air dispersion and healthcare contamination, HFNC may be less dangerous. This data suggests that NIPPV should be considered cautiously. Closed-circuit systems with appropriate filters in place are important, as are well-fitting masks and the absence of facial hair on the patient, allowing for tight seals [3]. Helmet BiPAP with an air cushion in place around the neck is safe and should be used if available [3]. All other forms of NIPPV have been associated with higher dispersal distances than high flow oxygen systems and concern for increased risk of nosocomial and healthcare provider infection [3].

Compared to NIPPV, HFNC is more dangerous regarding aerosol dispersion and contamination of healthcare personnel: we are not sure