Longitudinal Multiple Breath Washout Testing in Pediatric Patients after Hematopoietic Stem Cell Transplantation

Background : Children undergoing hematopoietic stem cell transplantation (HSCT) regimens are at risk of small airways disease. HSCT regimens including alkylating chemotherapeutic agents during conditioning, e.g. Busulfan, can induce small airway disease. The nitrogen multiple breath washout (N2MBW) test may detect small airway dysfunction more reliably compared to spirometry. However, N2MBW data in children undergoing HSCT are scant. Objective: To determine (i) the prevalence of abnormal lung function estimated by N2MBW and spirometry and (ii) lung function trajectories in children before and after HSCT with or without Busulfan. Methods: In this single-centered cohort study, we retrospectively analyzed clinical routine data at baseline and 5 years after HSCT from children undergoing HSCT between 2015–2022. Primary outcome was the lung clearance index (LCI) from N2MBW and forced expiratory volume in 1 second (FEV₁) from spirometry. Children were included if lung function was measured before and after HSCT. Abnormal lung function was defined as LCI> 1.64 or FEV1