Multiple breath washout in pediatric patients after lung transplantation

Forced expiratory volume in 1 second ( FEV 1 ) from spirometry is the most commonly used parameter to detect early allograft dysfunction after lung transplantation ( LT x). There are concerns regarding its sensitivity. Nitrogen‐multiple breath washout (N 2 ‐ MBW ) is sensitive at detecting early global (lung clearance index [ LCI ]) and acinar (S acin ) airway inhomogeneity. We investigated whether N 2 ‐ MBW indices indicate small airways pathology after LT x in children with stable spirometry. Thirty‐seven children without bronchiolitis obliterans syndrome [BOS] at a median of 1.6 (0.6‐3.0) years after LT x underwent N 2 ‐ MBW and spirometry, 28 of those on 2 occasions (≤6 months apart) during clinically stable periods. Additional longitudinal data (11 and 8 measurements, respectively) are provided from 2 patients with BOS . In patients without BOS , LCI and S acin were significantly elevated compared with healthy controls. LCI was abnormal at the 2 test occasions in 81% and 71% of patients, respectively, compared with 30% and 39% of patients with abnormal FEV 1 / forced vital capacity (FVC) . Correlations of LCI with FEV 1 / FVC ( r  = 0.1, P  = .4) and FEV 1 ( r  = −0.1, P  = .6) were poor. N 2 ‐ MBW represents a sensitive and reproducible tool for the early detection of airways pathology in stable transplant recipients. Moreover, indices were highly elevated in both patients with BOS . Spirometry and LCI showed poor correlation, indicating distinct and complementary physiologic measures.