Nitrogen dioxide production in a nitric oxide inhalation system using the Servo Ventilator 900C

During nitric oxide (NO) inhalation therapy, toxicity may be produced by the reactive metabolite nitrogen dioxide (NO₂). The purpose of the present study was to determine the NO₂ concentration in a NO inhalation system used for respiratory failure in children at relatively low concentrations of NO (< 20 ppm). The production of NO₂ in the NO inhalation system using the Servo Ventilator 900C connected to the test lung under each of 30 combinations of NO concentrations (0, 4, 8, 12, 16, and 19 ppm) and inspired oxygen (O₂) concentrations (21, 40, 60, 80, and 100%). Pressure controlled ventilation was used with a respiratory rate of 20 breaths/min. NO and NO₂ measurements were obtained on the inspiratory side of the Y-piece connected to the test lung. At a given NO level, increases in the concentration of inspired O₂ resulted in increases in the concentration of NO₂ produced, as did increases in the amount of NO at a given concentration of O₂. The mean NO₂ concentration at the inspiratory site of the Y-piece did not exceed 0.05 ppm (the limit of NO₂ as an outdoor air pollutant in the United States) when the NO concentration did not exceed 8 ppm, regardless of the O₂ concentration. NO inhalation therapy for children with severe respiratory failure using the Servo Ventilator 900C can be performed safely when the concentration of NO does not exceed 8 ppm.