(1186) Impact of High-Flow Nasal Cannula on Aerosol Production From Adult Airways

Introduction: High Flow Nasal Cannula (HFNC) devices provide heated and humidified continuous air flow. The flow generated can range from 1 liter per minute (LPM) to as high as 60 LPM. Like many other respiratory therapies, the use of this device is thought to generate aerosol. During the COVID-19 pandemic, the use of HFNC was initially discouraged for this reason but then widely adopted when personal protective equipment became more readily available. However, the aerosol generation with HFNC is not well described and it is not known if aerosol generation occurs at all flow levels. We therefore conducted a computer-based simulation study utilizing anatomically correct airway models to study the effect of HFNC at various flow rates and aerosol generation.

Methods: A computer-generated airway model was created to include the nasopharynx, oropharynx, hypopharynx, larynx, and trachea (Ansys FluentTM). Numerical simulations were setup to simulate breathing cycle and then aerosol particles were introduced both to resolve the dynamics of aerosol laden air inhaled and exhaled by a patient. The influence on aerosol generation (particle size 1µm) was studied at flow rates of 0, 3, 6 and 60 LPM in a 2-D airway model at a set respiratory rate of 12 breaths/minute and tidal volume of 500 ml.

Results: Our models show that at 0 LPM flow, aerosols accumulate within the airways during the first two breathing cycles, primarily during inhalations, with relatively small amount of outflow during exhalation. The outflow of aerosols occurs primarily via the mouth. With the subsequent breathing cycle, there is a sudden burst of aerosol outflow during exhalation, with an associated drop in aerosol mass within the airways. This behavior continues to be repeated with subsequent breathing cycles. As the cannula flow rates are increased, the amount of aerosol outflow through the mouth during exhalations increases with each breathing cycle and there is lower accumulation in the airways and lower outflow through the nose. However, the total mass of aerosol generated over a 20 second period at different flow rates is similar.

Conclusions: : Similar amount of aerosol generation occurs with HFNC at differing flow rates. Higher flow rates increases aerosol outflows through the mouth.