Nitrogen dioxide formation during inhaled nitric oxide therapy

Background: Nitrogen dioxide (NO2) is a toxic byproduct of inhalation thera py with nitric oxide (NO). The rate of NO2 formation during NO therapy is c ontroversial. Methods: The formation of NO2 was studied under dynamic flows emulating a b ase case NO ventilator mixture containing 80 ppm NO in a 90% oxygen matrix. The difficulty in measuring NO2 concentrations below 2 ppm accurately was overcome by the use of tunable diode laser absorption spectroscopy. Results: Using a second-order model, the rate constant, k, for NO2 formatio n was determined to be (1.19 +/- 0.11) x 10(-11) ppm(-2) s(-1), which is in basic agreement with evaluated data from atmospheric literature. Conclusions: Inhaled NO can be delivered safely in a well-designed, continu ous flow neonatal ventilatory circuit, and NO2 formation can be calculated reliably using the rate constant and circuit dwell time. (C) 1999 American Association for Clinical Chemistry.