title: Unpredictability of delivered bubble nasal continuous positive airway pressure: role of bias flow magnitude and nares-prong air leaks.
abstract: Nasal continuous-positive-airway-pressure (NCPAP) is popular for infant respiratory support. We compared delivered to intended intra-prong, proximal-airway, and distal-airway pressures using ventilator (V-NCPAP) and bubble (B-NCPAP) devices. Measurements were repeated at five flows (4, 6, 8, 10, and 12 L/min) and three NCPAP (4, 6, and 8 cm H2O) under no, small, and large nares-prong interface leak conditions. With no-leak, delivered B-NCPAP was systematically greater than intended levels at all pressure sites. The corresponding V-NCPAP flow-dependence was none-to-minimal. Prong and intra-airway B-NCPAP overshoots were also observed with small-leak, while only prong B-NCPAP showed a flow-dependent overshoot for large-leak. Leaks did not affect intra-prong V-NCPAP but resulted in progressively lower than desired, flow-independent intra-airway V-NCPAP. We conclude that the self-adjusting capability of ventilators allows closely matched actual versus intended V-NCPAP. Alternatively, for the range of flows used clinically, intra-prong and intra-airway B-NCPAP are systematically higher at increasing flows than operator-intended levels, even when appreciable nares-prong leak is present. Additionally, the oscillations (noise) characterizing B-NCPAP are substantially attenuated between the proximal and distal airways; therefore, it is unlikely that B-NCPAP engenders ventilation or lung recruitment via this phenomenon. Tubing submersion depth for setting the level of B-NCPAP is highly inaccurate, and operators should instead rely on intra-prong pressure measurement.
authors.affiliation: Department of Neonatal-Perinatal Medicine, Schneider Children's Hospital, NSLIJHS, New Hyde Park, New York 11040, USA.
authors.forename: Doron J
authors.initials: DJ
authors.lastname: Kahn
authors.forename: Sherry E
authors.initials: SE
authors.lastname: Courtney
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Steele
authors.forename: Robert H
authors.initials: RH
authors.lastname: Habib
mesh_terms: D045422:Continuous Positive Airway Pressure / Q000295:instrumentation / Q000379:methods; D006801:Humans; D007223:Infant; D008397:Masks; D008954:Models, Biological