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Effects of Flow Amplitudes on Intraprong Pressures During Bubble Versus Ventilator-Generated Nasal Continuous Positive Airway Pressure in Premature Infants

OBJECTIVES. The goal were to characterize the flow dependence of bubble nasal continuous positive airway pressure delivery in a cohort of preterm infants and to compare the actual (delivered) intraprong continuous positive airway pressure with the intended (set) nasal continuous positive airway pressure for both ventilator-generated nasal continuous positive airway pressure and bubble nasal continuous positive airway pressure delivery. A range of set values and constant flow rates were studied in the same preterm infants. METHODS. For 12 premature infants of <1500 g (birth weight: 1140 ± 267 g; gestational age: 28.5 ± 1.9 weeks; study age: 12.9 ± 8 days; all mean ± SD), intraprong pressures were measured at 3 increasing flow settings, repeated for set nasal continuous positive airway pressures (or desired immersion depths) of 4 and 6 cmH2O. Next, intraprong pressures were measured at bubble nasal continuous positive airway pressure expiratory tubing submersion depths and ventilator-generated nasal continuous positive airway pressure set expiratory pressures of 2, 3, 4, 5, and 7 cmH2O while the flow rate was held constant. RESULTS. Actual (delivered) intraprong pressure during bubble nasal continuous positive airway pressure delivery was highly flow dependent and increased as the flow rate increased. During ventilator-generated nasal continuous positive airway pressure delivery, actual pressure at the nasal prongs closely approximated the pressure set at the ventilator. During bubble nasal continuous positive airway pressure delivery at constant flow rate, the average delivered prong pressure was 1.3 cmH2O (range: 0.5–2.2 cmH2O) higher than that set through submersion of the expiratory tubing, and the relative difference between the set and actual pressures increased at lesser immersion depths. CONCLUSIONS. Prong pressure during bubble nasal continuous positive airway pressure delivery is highly variable and depends on the interaction of submersion depth and flow amplitudes.