Alternate gas washout indices: Assessment of ventilation inhomogeneity in mild to moderate pediatric cystic fibrosis lung disease.

Introduction: Normalized phase III slope (Sn ) indices from multiple breath washout (MBW) estimate ventilation inhomogeneity. Alternate (*) protocols for Sn indices exist, however the utility of these outcomes in children with mild-to-moderate cystic fibrosis (CF) is unknown.

Methods: We measured nitrogen MBW and spirometry in 135 children (43 controls) aged 4-18 years. We assessed validity, practicability, and reliability of Sn protocols. Outcomes included the ability to detect abnormal lung function, test agreement, measurement duration, intra-test repeatability, and quality.

Results: Lung clearance index (LCI) was abnormal in 80 (87%), Scond in 55 (60%), Scond* in 17 (19%), Sacin in 10 (11%), Sacin* in 11 (12%), and FEV in 28 (30%). Alternate protocols reduced measurement duration. Agreement of indices to detect abnormal lung function was poor. The quality of analysis and repeatability deteriorated with the alternate technique compared to standard.

Conclusion: In children with mild-to-moderate CF lung disease, alternate protocols seem practical but clinimetric properties of standard Sn protocols are preferable.