Objective: To evaluate the accuracy of a flow-proportional delivery system and the pattern of inspiratory nitric oxide (NO) concentration during different flow conditions.
Design: Laboratory study in a lung model.
Setting: University experimental laboratory.
Subject: With a new delivery system, NO was administered proportional to the inspiratory flow into the inspiratory circuit to deliver a NO concentration of 10 and 30 ppm to a test lung during different ventilatory modes (volume-controlled ventilation [VCV], pressure-controlled ventilation [PCV], and airway pressure release ventilation [APRV]) with a fraction of inspired oxygen (FIo2) of 1.0.
Interventions: During VCV and PCV, the flow pattern was varied to achieve tidal volumes of 300, 600, and 900 mL, respectively, with inspiratory to expiratory time ratios of 1:3, 1:2, and 1:1. APRV was studied at a minute volume of 6,12, and 18 L. Nitric oxides (NOx[NO+NO2]) and nitric dioxide (NO2) were monitored by chemiluminescence and electrochemical analysis. As the NO/N2 gas mixture is the only nitrogen source during ventilation with an FIo2 of 1.0, we evaluated the inspiratory fluctuation of the nitric oxides concentration by measuring the carrier gas (N2) concentration with a fast-response nitrogen analyzer.
Results: During all flow conditions, NOx concentration was stable but slightly higher than expected. Measured and expected mean concentrations differed <9% (mean, <4%). Inspiratory NOx concentration fluctuation derived from N2 concentration was significantly higher than expected at higher flow rates, but this difference was not detected by chemiluminescence or electrochemical analysis. The NO2 production was not affected by the flow rate and was always≤0.2 ppm (NO, 10 ppm) and ≤1.9 ppm (NO, 30 ppm).
Conclusion: The tested NO delivery module administered stable mean inspiratory NO concentrations. Although inspiratory NO concentration fluctuates depending on the inspiratory flow rate, this delivery device allows stable NO administration without requiring adjustments when ventilator settings are changed.