OCCULT NITRIC-OXIDE INHALATION IMPROVES OXYGENATION IN MECHANICALLY VENTILATED CHILDREN

Objectives: Auto-inhalation of nitric oxide (NO) produced in the upper airways may have physiologic effects on lung function. For intubated patients, the upper airway source of NO is eliminated, but the hospita l compressed air source from the environment is contaminated with vary ing levels of NO, creating an ''occult'' form of NO therapy. We examin ed the physiologic significance of occult inhaled NO in ventilator-dep endent pediatric patients. We hypothesized that very low levels of NO contamination in inspired gas improve Pao? in ventilator-dependent chi ldren. Study design: Inspired NO levels at the mouth were measured by chemiluminescence in 4 pediatric subjects with normal lungs and 3 with parenchymal lung disease. Subjects were sequentially ventilated with first standard hospital gas (H1), switched to pure nitrogen-oxygen at a similar FIO2 but with no NO contamination (A2), hospital gas again ( H2), the nitrogen-oxygen (A2) to control for time and sequence, and fi nally the nitrogen-oxygen mixture with supplemental NO in an amount eq ual to the NO previously measured in hospital gas (A2 + NO). Inhaled N O levels and PaO2 were recorded 15 minutes into each of the 5 steps. T wo patients were studied a second time, remote from their first examin ation. Results: NO levels in inhaled hospital gas mixtures ranged from 13 to 79 ppb (mean H1 = 53.3 +/- 23.7 ppb, mean H2 = 53.2 +/- 20.7 pp b, mean A2 + NO = 45 +/- 15.3 ppb; P <.0001). Removing NO from ventila tor gas decreased PaO2 in all subjects, whereas replacing NO, in artif icial gas restored PaO2 to baseline values (P <.0001). Conclusion: Con centrations of NO in hospital compressed air are variable and have phy siologic effects. The long-term implications of these findings remain to be defined.