Abstract
Background: High flow nasal cannula (HFNC) therapy delivers gas mixtures at flow rates typically exceeding patient inspiratory flow rates. Benefits of HFNC may include washout of CO2-rich exhaled gas from upper airways and provision of a positive distending pressure in the upper airways. Objectives: To understand the influence of cannula size, HFNC flow rate, and gas properties on tracheal pressure and CO2 clearance in adult nasal airway replicas. Methods: Five realistic adult nose-throat airway replicas were connected from the trachea to a breathing simulator (tidal volume = 500 ml, frequency = 18 breath/min, I:E ratio = 1:2). CO2 was supplied at the simulator to mimic CO2 in exhaled gas. Tracheal CO2 concentrations and pressures were measured during simulated breathing for HFNC flow rates of 0, 30, and 60 l/min of air, O2, and an 80/20 mixture of He/O2. Additionally, three cannula of varying size were compared. Results: Positive end expiratory pressure (PEEP) increased with flow rate. O2 and air both resulted in higher PEEP than He/O2. PEEP was also influenced by cannula size and airway geometry. Average CO2 concentration decreased significantly between 0 and 30 l/min flows, but did not appreciably differ between 30 and 60 l/min flows. CO2 concentration was lower for He/O2 than for air or O2. Conclusions: Airway pressures increased with flow rate and were lower for He/O2 than for air or O2. CO2 clearance appeared to plateau for air and O2 between 30 and 60 l/min, but was significantly improved using He/O2.
Published Version
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