GENERATION OF NITROGEN-DIOXIDE DURING NITRIC-OXIDE THERAPY AND MECHANICAL VENTILATION OF CHILDREN WITH A SERVO 900C VENTILATOR

Objective:To determine the combinations of nitric oxide (NO), oxygen ( O-2), minute ventilation (MV) and total gas flow (TGF) which generate toxic concentrations of nitrogen dioxide (NO2) during mechanical venti lation with a Servo 900C ventilator. Design: The measurement of NO2 ge nerated with NO (20, 40, 60, 80, 100 ppm) and O-2 [fractional inspired oxygen (FIO2) 0.21, 0.4, 0.6, 0.9] during mechanical ventilation with MVs of 2.5, 5.0 and 7.5 l/min and TGFs from 2 to 14 l/min. Setting: L aboratory of intensive care unit in paediatric tertiary hospital. Resu lts: Toxic concentrations of NO2 (> 5 ppm) were generated in the venti lator circuit when NO was 80 ppm or 100 ppm in FIO2 of 0.6 or 0.9 with MVs of 2.5, 5.0 and 7.5 l/min; and with SO ppm NO in FIO2 of 0.6 at a ll TGFs from 2.0 to 13.6 l/min and MVs of 2.5, 5.0 and 7.5 l/min (TGF/ MV 0.3-5.4). NO2 1.5-2.6 ppm was generated with 40 ppm NO in FIO2 of 0 .6, TGFs 2.1-13.7 l/min, and MVs 2.5, 5.0 and 7.5 l/min (TGF/MV 0.3-5. 5). NO2 0.9-0.6 ppm Was generated with 20 ppm NO in FIO2 of 0.6, TGFs 2.5-13.8 and MVs 2.5, 5.0 and 7.5 (TGF/MV 0.3-5.5). NO2 generation was not affected significantly by the TGF/MV ratio. Conclusions: The gene ration of NO2 in the ventilator circuit is directly proportional to co ncentration of NO and O-2 and inversely proportional to the TGF and MV but uninfluenced by the TGF/MV ratio. NO 80 ppm, but neither 20 nor 4 0 ppm in FIO2 of 0.6, generates toxic NO2 irrespective of TGF, MV or t he TGF/MV ratio.