Improving the Safety of High-Flow Therapies in the Management of Patients With COVID-19

To the Editor:

The use of high-flow therapies and noninvasive ventilation in the management of respiratory failure developed in many patients with coronavirus disease 2019 (COVID-19) represents a great challenge for health-care workers because these respiratory support procedures could increase virus aerosolization. They can be considered as independent risk factors for the spread of infection.^{1 , 2} Several measures are supposed to be taken while treating patients with COVID-19 with ventilation modalities, such as patient isolation in adequately ventilated or negative pressure rooms, limiting the number of individuals in the isolation room, and wearing protective respirators by health-care workers.^{3 , 4} Also, using a properly fitted patient interface with minimal air leaks is highly suggested to increase the safety of such procedures. The study presented by Leonard et al⁵ in a recent issue of CHEST (September 2020) gives a clear vision on how a surgical mask placed over the face during the use of high-flow therapy can participate in reducing the velocity of the gas exhaled and the dispersion of aerosol droplets into the surrounding environment through the use of a computational fluid dynamic technique. This technique enables the simulation of design and off-design conditions and accident scenarios of any engineered system.⁶ The present trial represents a great step toward achieving the optimal control of aerosol generation during high-flow therapies, especially in patients with COVID-19 with early stages of respiratory failure where gas flow rates > 6 L/min are required with keeping other safety precautions. Leonard et al⁵ best answered three important questions in this trial: (1) how the added mask affects the velocity of the delivered gas, (2) how the leakage either intentional or unintentional around the mask affects the extent of particles capture, and (3) what are the consequences of adding that mask on one of the important physiological benefits of high-flow therapy (eg, nasopharyngeal dead space washout). However, a fully comprehensive study is needed to test the impact of adding a surgical mask on all clinical benefits of high-flow therapy, besides the tolerability of the patient to such adjustment in the well-known procedure. Only one high gas flow of 40 L/min was tested here, but what about flows higher than that level, which is likely to be needed in certain patient conditions? Other high flow is needed to be tested to know whether these flows will show similar behavior as that of 40 L/min or not, especially with the recommendation of the authors to use flows > 40 L/min to overcome the reduction in CO₂ flushing in a patient with increased work of breathing.