Comparison of two administration techniques of inhaled nitric oxide on nitrogen dioxide production.

The purpose of this study was to verify whether, compared with the introduction of the NO-N2 mixture at the air inlet of the ventilator (classical method), a direct injection of NO-N2 into the inspiratory line of the ventilator circuit with a new injection device (new method), would reduce NO2 formation by reducing contact time between O2 and NO. The effect of two FIO2(0.21 and 0.90) and NO concentrations on NO2 production was determined. In the classical method, NO and O2 were mixed with an air/oxygen blender before the gas mixture entered the ventilator. In the new method, NO was injected directly into the respiratory line with the injection system. Nitric oxide and nitrogen dioxide gases were measured using a chemiluminescence analyzer. For a FI02 of 0.90 and 90 ppm of NO2, the amount of NO2 produced was decreased from 8.9 +/- 0.8 ppm (mean +/- SD) with the classical injection system to 4.4 +/- 0.2 ppm with the new injection system (P = 0.0039, Mann-Whitney test), and NO2 production was decreased from 4.5 +/-0.2 ppm to 2.1 +/- 0.4 ppm (P = 0.02) at 60 ppm of NO. However, at a FIO2, no difference was found in the amount of NO2 produced. We conclude that, compared with the classical method of NO administration, the new NO injection system reduces considerably the concentration of inhaled NO2 when a high FIO2 and a high concentration of NO are used.