Evaluation of Four Analyzers Used to Monitor Nitric Oxide and Nitrogen Dioxide Concentrations during Inhaled Nitric Oxide Administration

Abstract

BACKGROUND: The verification of nitric oxide (NO) doses and the measurement of nitrogen dioxide (NO2) levels are essential in evaluating physi-ologic response and ensuring safe delivery during inhaled NO therapy. We conducted a 2-part evaluation of 4 NO-NO2 analyzers: Pulmonox® II (PMX), Bedfont NOxBOX (BFX), Dräger PacII NO and 190 NO2 (DRG), and Ther-moenvironmental 42M (42M). METHODS: The analyzers were calibrated according to manufacturers’ specifications. Part 1: 7 predicted NO con-centrations [NO] ranging from 3 to 80 ppm were titrated into the main gas flow of a pressure-limited infant ventilator connected to a test lung and set in the IMV mode at a frequency of 30 breaths/min, PIP/PEEP of 30/5 cm H2O, T₁ of 0.06 s, and FDO2 of 0.30, 0.60, and 1.0. Each analyzer was studied inde-pendently and NO-NO2 levels were recorded after 5 minutes of stabilization. Measurements were repeated 3 times, and mean values were used for statistical analysis. Measured NO levels were compared to predicted [NO]. Part 2: The study was repeated using 5 predicted NO2 concentrations [NO2] ranging from 1 to 8 ppm, at an FDO2 of 0.21. Measured NO2 levels were compared to pre-dicted [NO2]. RESULTS: Part 1: The bias ± precision values were: PMX -0.06±1.13 ppm, BFX-0.67±0.34 ppm, DRG 1.48±1.09 ppm, and 42M-1.10 ± 1.11 ppm. NO2 levels differed among the 4 analyzers. The BFX and 42M measured significantly higher NO2 levels than the PMX and DRG (p < 0.001). Part 2: The bias ± precision values were: PMX 0.16 ± 0.75 ppm, BFX -0.29 ±0.25 ppm, DRG 0.39 ± 0.33 ppm, and 42M -0.10 ±0.25 ppm. CONCLU-SIONS: NO measurements compared favorably to predicted [NO] with the 4 analyzers and are suitable for clinical use. All 4 analyzers provide precise NO2 readings in a mixture of room air and NO2 but provide different NO2 readings in a gas mixture of NO2 with O2 > 0.21. The PMX and DRG are main-stream analyzers and the BFX and 42M are sidestream. The difference in sam-ple technique may account for the difference in NO2 readings across these 4 analyzers.