Feasibility and Utility of Multiple Breath Washout Measured Scond and Sacin in Preschool Children With Cystic Fibrosis.

Background: The lung clearance index (LCI) is a sensitive measure of global ventilation inhomogeneity but does not describe the gas mixing mechanisms that lead to inhomogeneity. Multiple breath washout normalized phase III slope (SnIII) metrics may complement LCI when assessing lung disease; Scond describes convection-dependent inhomogeneity and Sacin reflects diffusion convection-interaction-dependent inhomogeneity respectively. We aim to determine the feasibility and utility of Scond and Sacin in preschool children with CF.

Methods: We retrospectively assessed Scond and Sacin in successful MBW tests performed on preschool children. Scond and Sacin were calculated by visual breath-by-breath analysis according to ATS/ERS MBW consensus statement, with the exception that minimum SnIII was at least 30% of expired volume rather than between 65% and 95% of expired volume.

Results: We analyzed MBW tests for 40 healthy controls and 40 participants with CF, with a mean (range) baseline age of 4.1 years (2.6-5.9). Of the 372 successful MBW tests analyzed, 77% had reportable SnIII indices. Scond was elevated in CF relative to controls (∆ 0.037; 95% CI: 0.026-0.047; p < 0.001). Both within- and between-test variability was higher for Scond and Sacin than for LCI. More clinically stable test occasions were above the upper limit of normal for Scond than for LCI (64% vs. 50%, p = 0.02).

Conclusions: MBW metrics Scond and Sacin are feasible in young children. While they differentiate preschool children with CF from healthy controls, SnIII indices are more variable than LCI, limiting their interpretability.