Pulmonary function in children after hematopoietic stem cell transplantation: a retrospective analysis

<bold>Background:</bold> Conditioning-related toxicity and immunological reactions may impact pulmonary function after hematopoietic stem cell transplantation (HSCT). While spirometry detects alterations of large airways mainly, the nitrogen multiple breath washout (N2MBW) test evaluates damage to small airways. The aim of this study was to assess the evolution of lung function in pediatric patients undergoing HSCT after busulfan-based conditioning. <bold>Methods:</bold> Medical charts of all patients undergoing HSCT between 2015-2022 at the University Children’s Hospital Zurich were retrospectively analyzed. Development of the lung clearance index (LCI) from N2MBW and forced expiratory volume in 1 second (FEV1) from spirometry after HSCT was analyzed. Patients aged ≥6 years having at least one LCI measurement before and after HSCT were included. <bold>Results:</bold> 130 out of 265 patients met the age inclusion criteria and performed N2MBW tests. N=48/130 (37%) had qualitative acceptable LCI measurements before and after HSCT, with a follow-up time of median 23 months (min.0.71-max.83.7months). Abnormal test result was defined as z-score +1.64 for LCI and -1.64 for FEV1. Among patients receiving Busulfan, 11 out of 16 (68.7%) had abnormal LCI values compared to 5 out of 16 (31.2%) with abnormal FEV1 values. Busulfan treated patients had significantly higher LCI-values compared to non-treated ones. Mean LCI z-scores were 3.38 (IQR: 0.614 to 5.275) in Busulfan treated patients versus 1.19 (IQR: -0.544 to 1.824) in non-treated ones (p-value:<0.001). <bold>Conclusion:</bold> Following conditioning and HSCT, N2MBW identified more cases of pulmonary damage compared to spirometry. Busulfan treatment may lead to pulmonary impairment.