Offline exhaled nitric oxide in children: chemiluminescence vs. electrochemical devices

Background: Exhaled nitric oxide (eNO) is a noninvasive marker of airway inflammation that can be measured by the “online” or “offline” technique. There are few articles that measure “offline” eNO in children at tidal volume and to our knowledge there is no article that compares the concordance and correlation between 2 different technologies measured offline at tidal volume. Objective: is to report the concordance and correlation of the eNO results obtained with a chemiluminescence vs. an electrochemical device by the “offline” technique at tidal volume. Methods: A cross-sectional, observational and prospective study was conducted in the National Institute of Respiratory Diseases, Mexico City. Healthy children and those with any lung disease between 1 and 11 years of age were included. The exhaled air sample was obtained at tidal volume by attaching a mask with a connection to a Mylar® bag. Results: 36 children were studied. The average (±SD) age of the study population was 6 ± 2.6 years; 25% of subjects included were healthy, and the rest had lung disease. The concordance correlation coefficient between the two measuring devices was 0.98 (p<0.001), with an average difference of 1.46 ± 3.5 ppb and 95% limits of agreement from -5.3 ppb to 8.3 ppb. The linear regression model equation for the estimation of eNO was eNO,cl = (eNO,eq· 1.0718) – 0.1343, (r2 = 0.97) Conclusion: The measurement of eNO by the “offline” method at tidal volume can be analyzed by electrochemical devices, and the results are interchangeable with those analyzed by chemiluminescence technology.