LAUSR

INTRODUCTION Recent studies indicate limited utility of nitrogen multiple breath washout (N2MBW) in infancy and advocate for using sulphur hexafluoride (SF6)MBW in this age group. Modern N2MBW systems, such as EXHALYZER D® (ECO MEDICS AG, Duernten, Switzerland), use O2 and CO2 sensors to calculate N2 concentrations (in principle: N2%=100-CO2%-O2%). High O2 and CO2 concentrations have now been shown to significantly suppress signal output from the other sensor, raising apparent N2 concentrations. We examined whether improved Exhalyzer D® N2-signal, accomplished after thorough examination of this CO2 and O2 interaction on gas sensors and its correction, leads to better agreement between N2MBW and SF6MBW in healthy infants and toddlers. METHOD Within the same session 52 healthy children aged 1-36 months (mean 1.30 (SD 0.72) years) completed SF6MBW and N2MBW recordings (EXHALYZER D®, SPIROWARE® version 3.2.1) during supine quiet sleep. SF6 and N2 SPIROWARE® files were re-analyzed off-line with in-house software using identical algorithms as in SPIROWARE® with or without application of the new correction factors for N2MBW provided by ECO MEDICS AG. Results Applying the improved N2-signal significantly reduced mean (95% CI) differences between N2- and SF6MBW recorded functional residual capacity (FRC) and lung clearance index (LCI): for FRC, from 26.1 (21.0; 31.2) mL p<0.0001 to 1.18 (-2.3; 4.5) mL p=0.5, and for LCI, from 1.86 (1.68; 2.02) p<0.001 to 0.44 (0.33; 0.55) p<0.001. CONCLUSION Correction of N2-signal, for CO2 and O2 interactions on gas sensors resulted in markedly closer agreement between N2MBW and SF6MBW outcomes in healthy infants and toddlers.