Nitric oxide supplied from a 10% source provides inhaled therapy without lowering inspired oxygen fraction

The authors designed a low-deadspace system to deliver inhaled nitric oxide from a high-concentration (10%) source. Nitric oxide, nitrogen dioxide, and O 2 concentrations were compared under simulated inhaled nitric oxide therapy (in vitro) from low (0.08%, 800 ppm) and high (10%, 100,000 ppm) sources of nitric oxide in nitrogen. O 2 concentrations remained above 99% and nitrogen dioxide below 3 ppm for nitric oxide delivered at dosages up to 180 ppm from the 10% source. An acute toxicity trial (in vivo) was also performed in nine rabbits mechanically ventilated with 100% 02 for four hours. Six rabbits received 80 ppm nitric oxide from a 10% source and three control rabbits received only O 2 . Nitric oxide, nitrogen dioxide, and O 2 concentrations were monitored in the ventilator circuit. Methemoglobin, arterial blood gases, arterial blood pressure, and heart rate were sampled every hour. At the 80-ppm nitric oxide dose, an average of 1.1 ± 0.2 ppm of nitrogen dioxide was produced within the ventilator circuit. Arterial methemoglobin in rabbits that received nitric oxide rose by 0.5% from baseline, compared with a 0.2% rise for controls (p = 0.001). The authors conclude that inhaled nitric oxide therapy can be provided from a high-concentration source. Because this system does not reduce inspired O 2 fraction, it may be more appropriate than low-source-concentration nitric oxide delivery systems for testing the efficacy of inhaled nitric oxide as an adjunct to optimal conventional medical therapy.