MULTIPLE BREATH WASHOUT PHASE III SLOPE INDICES IN PRESCHOOL CHILDREN WITH CYSTIC FIBROSIS: FEASIBILITY AND CORRELATION WITH LUNG CLEARANCE INDEX

Abstract

Introduction/Aim: Multiple breath washout (MBW) detects early lung disease in people with cystic fibrosis (pwCF), with lung clearance index (LCI) the commonly reported outcome. MBW-derived phase III slope (SnIII) indices provide additional insights into location of ventilation inhomogeneity, with Scond potentially detecting early impairment before LCI abnormalities. There is limited data on the feasibility of SnIII analysis in preschool children, a critical age for early clinical testing. This study aimed to evaluate the feasibility of obtaining SnIII indices in preschool pwCF and to explore their relationship with LCI. Method: A retrospective analysis was conducted on MBW data in pwCF (aged 3-6 years) at Queensland Children's Hospital over a 12-month period (August 2023-2024). Test occasions were randomly selected from those deemed technically acceptable for LCI. SnIII indices were manually inspected and analysed following ERS/ATS guidelines, with tests meeting the acceptability criteria for at least 2 MBW trials included. Descriptive statistics summarised cohort demographics, while regression models assessed associations between LCI and SnIII indices. Results: Data from 45 pwCF (51% female, mean (SD; range) age 4.9 (1.2; 2.7-6.8) years were included. SnIII indices were feasible in 72% (32/45) of occasions: Scond and Pacin in 69% (31/45) and Sacin in 47% (21/45). Increased LCI was not associated with a statistically significant change in Scond (β = 0.005, 95%CI -0.004, 0.014, p = 0.28), but was associated with significant increases to both Sacin (β = 0.11, 95%CI 0.075, 0.14, p < 0.001) and Pacin (β = 0.14, 95% CI -0.11, 0.17, p < 0.001). Conclusion: In a busy clinical setting two-thirds of preschool pwCF successfully achieved Scond and Pacin indices. Contrary to previous reports, LCI was associated with increases in Sacin and Pacin, but not Scond, based on thresholds for abnormality. These findings highlight feasibility of SnIII analysis in clinical MBW data. Future work will focus on increasing numbers and applicability of these published abnormality thresholds to the preschool population.