Evaluation of two electrochemical monitors for measurement of inhaled nitric oxide

Inhaled in low concentrations, nitric oxide (NO) acts as a potent pulmonary vasodilator, but when inhaled in high concentrations NO and its metabolite NO2 are potentially toxic molecules. Thus, an accurate and reproducible measurement of both NO and NO2 is necessary, and changes in NO concentration need to be detected instantly to avoid lung damage (high concentrations) or failure of NO therapy (low concentrations; unnoticed interruption of NO supply). We investigated two electrochemical NO monitors (Sensor Stik 4586 and Dräger PAC II) for accuracy and time constants. Both provided accurate and reproducible results at different NO concentrations. Known NO concentrations (standards: 10, 50, 75 ppm) were detected within a 3% tolerance, and acceptable time constants were seen when NO concentration was abruptly increased from zero to 50 ppm. The display read the final value within 60 s with the Sensor Stik and 11 s with the Dräger PAC II. Significant differences were seen when the NO concentration was rapidly reduced from 50 ppm to zero. The Sensor Stik took more than 2 h to reach zero, whereas the PAC II took 60 s.