The effect of spirometry on multiple breath washout outcomes in children with cystic fibrosis

Abstract

Multiple breath nitrogen washout (MBW) measurements in children with cystic fibrosis (CF) are often performed prior to spirometry, since forced-expiratory maneuvers could affect MBW outcomes as previously demonstrated in infants (Subbarao et al. Pediatr Pulmonol 2016). The objective of this study was to determine effects of spirometry on MBW outcomes in school-age children with CF. Children with CF between 6 and 18 years hospitalized for treatment of pulmonary exacerbations were included. MBW was performed during the second week of hospital admission using the Exhalyzer D (Eco Medics AG, Duernten, Switzerland) prior to spirometry (Easy on-PC, Ndd, Zurich, Switzerland) and repeated immediately after. MBW outcomes included lung clearance index (LCI), forced residual capacity (FRC) and cumulative expired volume (CEV). Wilcoxon signed-rank test was used to compare MBW outcomes pre and post spirometry. Fifteen children with CF (median age of 15 years, 73% female) completed the protocol. The median LCI prior to spirometry was 13.1 (IQR, 11.4-16.8); LCI post-spirometry was 12.9 (IQR, 11.5-15.7). There was no significant difference in LCI after spirometry (mean difference 0.04, 95% CI -0.54-0.63; relative difference -2.0%; p=0.99). There was no difference in FRC (relative difference 1.9%; p=0.95) or CEV (relative difference 0.6%; p=0.65). Upon Bland Altman analysis, the observed difference in LCI was not related to its magnitude and was within the normal biological variability of the test (Oude Engberink et al. Eur Respir J 2017). Performing spirometry before MBW had no effect on outcomes and may allow for greater flexibility for its use in clinical practice. Supported by The Irwin Foundation