Improved agreement between N2 and SF6 multiple-breath washout in healthy infants and toddlers with improved EXHALYZER D sensor performance

Recent studies indicate limited utility of nitrogen multiple-breath washout (N2MBW) in infancy and advocate for using sulfur hexafluoride (SF6) MBW in this age-group. Modern N2MBW systems, such as EXHALYZER D (ECO MEDICS AG, Duernten, Switzerland), use O-2 and CO2 sensors to calculate N-2 concentrations (in principle, N-2% = 100 - CO2% - O-2%). High O-2 and CO2 concentrations have now been shown to significantly suppress signal output from the other sensor, raising apparent N(2 )concentrations. We examined whether improved EXHALYZER D N-2 signal, accomplished after thorough examination of this CO2 and O-2 interaction on gas sensors and its correction, leads to better agreement between N-2 MBW and SF6 MBW in healthy infants and toddlers. Within the same session, 52 healthy children aged 1-36 mo [mean = 1.30 (SD = 0.72) yr] completed SF6 MBW and N-2 MBW recordings (EXHALYZER D, SPIROWARE version 3.2.1) during supine quiet sleep. SF6 and N-2 SPIROWARE files were reanalyzed offline with in-house software using identical algorithms as in SPIROWARE with or without application of the new correction factors for N-2 MBW provided by ECO MEDICS AG. Applying the improved N-2 signal significantly reduced mean [95% confidence interval (CI)] differences between N-2 MBW 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. Correction of N-2 signal for CO2 and O-2 interactions on gas sensors resulted in markedly closer agreement between N-2 MBW and SF6 MBW outcomes in healthy infants and toddlers. NEW & NOTEWORTHY Modern nitrogen multiple-breath washout (N2MBW) systems such as EXHALYZER D use O-2 and CO2 sensors to calculate N-2 concentrations. New corrections for interactions between high O-2 and CO2 concentrations on the gas sensors now provide accurate N-2 signals. The correct N-2 signal led to much improved agreement between N-2 MBW and sulfur hexafluoride (SF6) MBW functional residual capacity (FRC) and lung clearance index (LCI) in 52 sleeping healthy infants and toddlers, suggesting a role for N-2 MBW in this age-group.