Comparison of lung clearance index determined by washout of N2 and SF6 in infants and preschool children with cystic fibrosis

Background: Multiple-breath washout (MBW) has been shown to detect early impairment of lung function in children with cystic fibrosis (CF). Nitrogen (N-2) or sulfur hexafluoride (SF6) can be used as tracer gas for MBW. Recent data indicated higher lung clearance index (LCI) values measured with N-2-MBW than concurrent SF6-MBW in older children and adults, however, a comparison in infants and younger children, as well as to other outcome measures of CF lung disease is pending. Methods: N-2- and SF6 -MBW were performed consecutively in 31 sedated infants and preschool children with CF (mean age, 2.3 +/- 0.8 years) and 20 controls (mean age, 2.3 +/- 1.1 years) using the Exhalyzer D system. Children with CF also underwent chest magnetic resonance imaging (MRI). Results: Mean difference (95% CI) in LCI between N-2- and SF6-MBW was 1.1 +/- 0.4 (0.9 to 1.3) in controls and 2.1 +/- 1.9 (1.4 to 2.8) in CF. Agreement between N-2- and SF6-LCI was poor in children with CF. N-2-LCI and SF6-LCI correlated with MRI, however N-2-LCI showed a higher concordance with MRI than SF6-LCI. The absolute difference between N-2- and SF6-LCI values increased with the severity of CF lung disease as determined by MRI scores. Conclusion: N-2-LCI values were higher than SF6-LCI values in infants and preschool children with CF and controls. Better concordance of N-2-LCI than SF6-LCI with chest MRI scores point towards of a higher sensitivity of N-2-LCI to detect early lung disease in children with CF. (C) 2018 European Cystic Fibrosis Society. Published by Elsevier B.V. All rights reserved.