Generation of nitrogen dioxide during nitric oxide therapy and mechanical ventilation of children with a Servo 900C ventilator.

Abstract

To determine the combinations of nitric oxide (NO), oxygen (O2), minute ventilation (MV) and total gas flow (TGF) which generate toxic concentrations of nitrogen dioxide (NO2) during mechanical ventilation with a Servo 900C ventilator. The measurement of NO2 generated with NO (20, 40, 60, 80, 100 ppm) and O2 [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. Laboratory of intensive care unit in paediatric tertiary hospital. Toxic concentrations of NO2 (> 5 ppm) were generated in the ventilator 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 80 ppm NO in FIO2 of 0.6 at all 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. The generation of NO2 in the ventilator circuit is directly proportional to concentration of NO and O2 and inversely proportional to the TGF and MV but uninfluenced by the TGF/MV ratio. NO 80 ppm, but neither 20 nor 40 ppm in FIO2 of 0.6, generates toxic NO2 irrespective of TGF, MV or the TGF/MV ratio.