Nitrogen Dioxide Formation during Inhaled Nitric Oxide Therapy

Background: Nitrogen dioxide (NO2) is a toxic by-product of inhalation therapy with nitric oxide (NO). The rate of NO2 formation during NO therapy is controversial. Methods: The formation of NO2 was studied under dynamic flows emulating a base 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 formation was determined to be (1.19 ± 0.11) × 10−11 ppm−2s−1, which is in basic agreement with evaluated data from atmospheric literature. Conclusions: Inhaled NO can be delivered safely in a well-designed, continuous flow neonatal ventilatory circuit, and NO2 formation can be calculated reliably using the rate constant and circuit dwell time.