Monitoring nitric oxide: a comparison of three monitors in a paediatric ventilator circuit

Simultaneous measurements of nitric oxide (NO) (0-80 ppm) using a chemiluminescence monitor and two electrochemical monitors were performed during simulated paediatric mechanical ventilation. The mean difference (bias) between the chemiluminescence (Model 42H Thermo Environmental Instruments Inc) and an electrochemical monitor (Pulmonox Research and Development Corp) was 0.52 +/- 6.52 ppm (SD). The 95% confidence limits of the mean difference were 3.00 to -1.96 ppm and the limits of agreement between the two techniques were 13.56 to -12.52 ppm. The mean difference between the chemiluminescence monitor and another electrochemical monitor (NOxBox, Bedfont Scientific Inc) was -7.27 +/- 4.29 ppm. The 95% confidence limits of the mean difference were -9.02 to -5.56 ppm and limits of agreement of the two techniques were -16.13 to 1.55 ppm. These results suggest that electrochemical monitors may be used to guard against potentially toxic concentrations of NO (greater than 20 ppm). However they do not suggest that either of the electrochemical monitors may be used with confidence in lieu of the chemiluminescence monitor to regulate NO at low clinical NO levels (1-5 ppm).