Introduction: Mulitple-breath washout (MBW) is a sensitive tool to detect abnormalities in early cystic fibrosis (CF) lung disease. Recently, a software error was found in the commonly used spiroware software with the Exhalyzer D. As the correction applies to the nitrogen-derived MBW, its impact on previous results and the clinical implication is of interest.

Methods: Previously published results were reanalyzed with the adjusted spiroware software version 3.3.1 to compare consecutive sulfur hexafluoride (SF₆)- and nitrogen(N₂)-MBW in 20 healthy controls and 31 infants with CF. Children with CF then underwent chest magnetic resonance imaging (MRI) on the same day.

Results: The corrected N₂-lung clearance index (LCI_cor) decreased significantly in healthy and children with CF compared to the previous LCI (LCI_prev) (P=0.001). Despite an approximation and a significant correlation of N_2cor- and SF₆-LCI (P=0.03), the N₂-LCI_cor remained significantly higher than SF₆-LCI (P<0.01). The adjusted upper limit of normal of N₂-LCI_cor led to a different health-disease classification of nine children with CF. The comparison between N₂-LCI_cor and MRI score showed a good correlation which was best regarding the MRI perfusion score (P<0.01-0.001). A more detailed analysis of N₂-LCI_cor and MRI in a larger cohort is currently underway and results will be available at the conference.

Conclusion: Consequently, the error correction has led to a significant decrease of the corrected N₂-LCI which is slightly, but significantly higher than the SF₆-LCI. The results with different tracer gases remain not interchangeable and key findings of previous observational studies can be confirmed.