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 H 2 O) 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 noneto-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 intraprong V-NCPAP but resulted in progressively lower than desired, flow-independent intra-airway V-NCPAP. We conclude that the selfadjusting 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. (Pediatr Res 62: [343][344][345][346][347] 2007) N CPAP is an increasingly popular mode of respiratory support in preterm infants with varying pulmonary disorders. The renewed interest in this form of ventilatory support aims at preventing collapse of the alveoli and terminal airways during expiration while relying on the infant's spontaneous respiration, and thereby avoids both the risk of tracheal intubation and concerns about ventilator-induced lung injury (1,2).A variety of devices are currently used for NCPAP delivery in infants. Most commonly, an infant ventilator is used to generate positive pressure. Flow is continuous and NCPAP pressure can be changed as desired by using the ventilator's positive end-expiratory pressure control. Ventilators maintain the delivered NCPAP pressure (V-NCPAP) close to the set pressure by automatic adjustments at the expiratory valve. Another device, B-NCPAP, has become a focus of interest as it is relatively inexpensive, easy to use, and favored by an institution reporting a low incidence of chronic lung disease (3). Warmed, humidified gas flows to the infant via the NCPAP circuit, binasal prongs are used, and the expiratory limb of the NCPAP tubing is submerged underwater to a depth in centimeters equal to the desired NCPAP. Flow rate is adjusted until gas bubbles through the water chamber. A hypothesized benefit to gas exchange and lung recruitment during B-NCPAP, the high-frequency oscillatory content of the b...

Bubble and ventilator-derived nasal continuous positive airway pressure in premature infants: work of breathing and gas exchange

“…6 We have previously shown in both a lung model and in premature infants that pressure delivered to the nasal prongs in a B-NCPAP system is greater than the immersion depth of the expiratory tubing, even at the lowest flow that causes gentle continuous bubbling. 9,10 We also showed that this pressure overshoot was systematically greater as the flow magnitude increased. By comparison, V-NCPAP-delivered pressures were equal to the set (desired) pressures and exhibited little flow dependence.…”

“…We have previously shown that this tubing length minimally affects the pressure at the prongs. 9 Hudson prongs (Hudson Respiratory Care, Temecula, CA, USA) were used in all infants on both devices. The largest prongs that fit comfortably in the infant's nares without blanching the surrounding tissue were used.…”

“…In addition, as with any CPAP modality, the effective intrapulmonary NCPAP delivery was substantially influenced by air leaks. 9,10 Few studies exist comparing B-NCPAP to V-NCPAP and it is unknown whether some of these studies ensured equivalent delivered pressures rather than just equivalent set pressures. Lee et al 4 compared two devices in 10 endotracheally intubated infants and found decreased minute volume and respiratory rate (RR) with B-NCPAP, but no differences in transcutaneous (Tc) O 2 or TcCO 2 .…”

Comparison of HFNC, bubble CPAP and SiPAP on aerosol delivery in neonates: An in‐vitro study

“…Nevertheless, this study was the first to compare B-NCPAP and V-NCPAP in preterm infants at equivalent delivered nasal prong pressures. Kahn, Courtney, Steele, and Habib (2007) performed a study to compare the actual delivered pressure versus the intended pressure through intra-prong, proximalairway, and distal-airway via V-NCPAP and B-NCPAP devices. The settings that they used in their study were flow rates of 4, 6, 8, 10, and 12 LPM and NCPAP levels of 4, 6, and 8 cm H 2 O.…”

“…In addition, a constant set pressure and intra-prong pressure were maintained on all devices tested in this study, except the intratracheal pressure. Previous studies have shown that the actual delivered intra-airway pressure could be different from the set pressure with CPAP systems (Kahn et al, 2007). Moreover, a variety of drug delivery devices are used in clinical settings, but this study examined only one type of nebulizer.…”