Practicability of nitrogen multiple-breath washout measurements in a pediatric cystic fibrosis outpatient setting

Background Although lung clearance index (LCI) is a sensitive indicator of mild cystic fibrosis (CF) lung disease, it is rarely measured due to lengthy protocols and the commercial unavailability of multiple-breath washout (MBW) setups and tracer gases. We used a newly validated, commercially available nitrogen (N₂) MBW setup to assess success rate, duration, and variability of LCI within a 20 min timeframe, during clinical routine. We also evaluated the relationship between LCI and other clinical markers of CF lung disease. Methods One hundred thirty six children (83 with CF) between 4 and 16 years were studied in a pediatric CF outpatient setting. One hundred eighteen out of 136 children were naïve to MBW. Within 20 min, each child was trained, N₂MBW was performed, and LCI was analyzed. We assessed intra- and between-test reproducibility in a subgroup of children. Results At least one LCI was feasible in 123 (90%) children, with a mean (range) of 3.3 (1.2-6.4) min per test. Two or more measurements were feasible in 56 (41%) children. Comparing LCI in CF versus controls, LCI mean (SD) was 12.0 (3.9) versus 6.1 (0.9), and the intra- and inter-test coefficient of repeatability was 1.00 versus 0.81 and 0.96 versus 0.62, respectively. LCI was correlated with spirometry, blood gases, and Pseudomonas aeruginosa infection. Conclusions Using available N₂MBW equipment, LCI measurements are practical and fast in children. LCI is correlated with markers of CF lung disease. Longer timeframes would be required for triplicate N₂MBW tests in inexperienced children.