Normative data for the new setup of the SF6 multiple-breath washout in unsedated infants

Background: The multiple-breath washout (MBW) with 4% sulphur hexafluoride (SF6) is a sensitive method to detect and monitor ventilation inhomogeneity (VI) in infancy. A new infant SF6 MBW methodology using currently available equipment was recently proposed. Aims: We compared lung clearance index (LCI) and functional residual capacity (FRC) outcomes in healthy infants from the new SF6 MBW technique with published normative data. Methods: Unselected healthy infants from the prospective Bern-Basel Infant Lung Development (BILD) birth cohort underwent MBW measurements using the new SF6 MBW technique (Spiroware 3.2; Ecomedics, Duernten, Switzerland). Measurements were performed in unsedated infants during quiet natural sleep according to the ATS/ERS standards. We report the mean (standard deviation (SD)), within-test coefficient of variation (CV), and upper limit of normal (mean + 1.64*SD). Results: We performed MBW measurements using the new method in 28 healthy infants. Two technically acceptable measurements were available in 23 healthy infants (82%) at ~5 weeks post-natal age (51% male, age: 5.5 weeks (0.9), weight: 4.5kg (0.6)). Mean FRC adjusted for weight was 17.2 (3.5) ml/kg (CV: 6.8%) and mean LCI was 7.2 (0.7) (CV: 9.7%, ULN: 8.3). These values differ considerably from published normative data using Wbreath software (FRC: 23.9 (4.0) ml/kg; LCI: 6.8 (0.6); Fuchs et al. 2011). Conclusions: Measurements from the new SF6 MBW setup generate FRC values approximately 30% higher and LCI 6% lower than for the former setup. These preliminary data highlight the need for new equipment specific reference values.