Carbon dioxide washout during high flow nasal cannula versus nasal CPAP support: An in vitro study

Summary Objective: To compare CO2 washout time at different levels of HFNC versus NCPAP in a premature infant lung model with simulated mouth‐closed and mouth‐open conditions using two sizes of nasal cannula and full‐ and half‐prong HFNC insertion depths. Design/Methods: A piston‐cylinder lung simulator, having a fixed volume of 30 ml and a 4.8 ml dead space, simulated spontaneous breathing (6.5 ml tidal volume, 50 br/min, Ti = 0.5 sec). Two Fisher & Paykel™ cannulas (Fisher & Paykel Healthcare Ltd., Auckland, New Zealand) (2.8 and 3.2 mm O.D.) and two Infant‐Flow™ (CareFusion, Yorba Linda, CA) NCPAP cannulas (3.4 and 4.1 mm O.D.) were applied to simulated airways having either 3.5 or 4.5 mm I.D. nares. Simulated mouth opening was a 5 mm I.D. side tap below the nasal interface. The lung was primed with 5% CO2. Washout times were determined at HFNC settings of 3, 4, 5, 6, and 8 L/min and NCPAP at 3, 4, 5, 6, and 8 cm H2O with simulated open and closed‐mouth conditions and full‐ and half‐inserted HFNC prongs. Results: Overall combined mean washout times for NCPAP with mouth‐closed were significantly longer than HFNC over all five pressure and flow device settings by 16.2% (P