Delivery characteristics of a combined nitric oxide nasal continuous positive airway pressure system

Background : Nitric oxide (NO), when inhaled, has a synergistic effect with airway recruitment strategies such as positive endexpiratory pressure (PEEP) or continuous positive airway pressure (CPAP) in improving oxygenation in lung injury. Methods : We modified a commercially available nasal CPAP (nCPAP) system to enable the concomitant delivery of inhaled NO (iNO) and nCPAP to neonates and term babies. Oxygen, NO and nitrogen dioxide (NO2 ) concentrations were measured, comparing the effects of using 50 or 1000 parts per million (p.p.m.) NO stock gas cylinders. Results : Stable and accurate delivery of iNO was found for both stock gas concentrations. Using a 50 p.p.m. NO stock gas resulted in limited NO2 formation, with a maximum inspired NO2 concentration of less than or equal to 0.3 p.p.m. (dose range up to 37 p.p.m. iNO), which was interpreted as the result of progressive dilution with nitrogen. In contrast, using a 1000 p.p.m. NO stock gas cylinder, inspired NO2 levels increased nonlinearly as expected with an increasing inspired concentration of NO. Conclusions : Inhaled NO can be safely and reliably delivered by the system we describe. The NO2 levels generated by the system are low, at least up to a dose of 37 p.p.m. NO, regardless of a stock gas concentration of 50 or 1000 p.p.m. NO. Using a 50 p.p.m. NO stock gas concentration, up to 80% oxygen can be given at 10 p.p.m. iNO.