Validation of nitrogen washout (N2-WO) for measurement of lung clearance index (LCI) and functional residual capacity (FRC) in preschoolers

Abstract

Introduction: Commercial N 2 -WO systems need modifications for use in young children and must be validated before widespread use. Aim: To compare LCI and FRC from Eco Medics Exhalyzer-D N 2 -WO to a custom-built AMIS 2000 Mass Spectrometer sulphur hexafluoride washout (SF 6 -WO) in preschool (3-6y)controls and patients with cystic fibrosis(CF) Methods: Washouts were performed on the same day. SF 6 -WO to standard lab protocol, N 2 -WO with a low deadspace filter and modified capnostat. A face mask with putty was used for all tests Results: 42 children were tested (25 CF). Mean age 5.1y CF, 4.8y, mean height and weight no difference CF vs. control . SF 6 -WO was not possible in 2 children, N 2 -WO was not possible in 6 Figure: Bland Altman (BA) plots for CF (black), Control (red), FRC (top) and LCI (bottom) FRC N2 was significantly higher than FRC SF6 in both groups. LCI N2 -LCI SF6 in controls showed good agreement. LoA were wider for children with CF, but there was no significant group difference (table 1). In children with CF only the BA plots suggest increased FRC N2 -FRC SF6 with increasing FRC, and decreased LCI N2 -LCI SF6 with increasing LCI (figure) Conclusion: Device specific reference values are needed for FRC and LCI in preschool children with CF.