Clinical monitoring of inhaled nitric oxide: comparison of chemiluminescent and electrochemical sensors.

In view of the rapidly increasing use of inhaled nitric oxide for infants with potentially reversible pulmonary hypertension, the ability to accurately measure nitric oxide and its by-products is an increasingly important safety issue. The authors evaluated the abilities of two chemiluminescent analyzers and two electrochemical sensors to detect known concentrations of nitric oxide (NO) and nitrogen dioxide (NO2). A calibrated mass spectrometer was utilized to determine the reference levels of NO2. Mass flowmeters calibrated with bubble flowmeters and an audited cylinder of NO were utilized to determine the levels of NO. In a test laboratory environment, all sensors yielded reasonably accurate measurements of NO. It was observed, however, that the amounts of NO recorded by the candidate analyzers in an 82% oxygen environment were slightly low compared with reference methods. The chemiluminescent analyzers consistently underread the true amounts of NO2 in a high-oxygen environment, producing negative concentrations on one instrument. Some monitors that are being clinically utilized to measure NO were designed for industrial and environmental applications in which the ambient oxygen concentrations are less than 21%. In the presence of higher oxygen concentrations, such analyzers can significantly underread the amounts of NO2 that are present, possibly because of reaction quenching or other effects. Measurements of NO and its by-products should be performed using analyzers that have been appropriately tested and calibrated with known concentrations of NO and NO2 prior to their clinical application.