Head-to-head comparison of single-breath and tidal-breath exhaled nitric oxide measurements

Background: Exhaled nitric oxide (eNO) is an endogenous gas involved in airway pathophysiology and is determined in orally exhaled air by various techniques. However, traditional single-breath technique (eNOSB) requires active cooperation and is not always easily practicable (especially in young children); simpler techniques including tidal breathing measurements (eNOTB) are not standardized. The aim of this study was to evaluate the possible correlation and correspondence between eNOSB and eNOTB and the impact of potential confounders in children with chronic adenotonsillar disease. Methods: Eighty-six children (mean age 8.7 ± 3.2 y) underwent eNO assessment by means of eNOSB and eNOTB. The correlation among eNOTB, eNOSB, and other potential confounders (i.e., gender, age, weight, height, BMI, and passive smoking exposure) were studied. Results: The analyses showed a poor correspondence between eNOSB and eNOTB, with the latter underestimating (P < 0.001) mean eNO values: 6.4 parts per billion (ppb) (95% confidence interval (CI): 8.4–11.4 ppb) vs. 9.8 ppb (95% CI: 5.6–7.3 ppb). A greater correlation was found between eNOSB and eNOTB in children younger than 6 y. Only eNOSB and age predicted eNOTB (R2 = 43.6%). Conclusion: eNOTB is not a good predictor of eNOSB in children. Constant-flow eNOSB is the technique of choice for eNO assessment in young children.