Impact of different breathing protocols on multiple-breath washout outcomes in children

BackgroundTo standardize multiple-breath washout (MBW) measurements, 1 L tidal volume (VT) protocols were suggested. The effect on MBW derived ventilation inhomogeneity (VI) indices is unclear.MethodsWe compared VI indices from free breathing MBW at baseline to 1 L VT MBW performed in triplicates in 35 children (20 with CF). Mean (range) age was 12.8 (7.0-16.7) years, weight 42 (20-64) kg and height 151 (117-170) cm.ResultsBaseline lung clearance index (LCI) increased from mean (SD) 11.0 (2.2) to 13.0 (2.6), p = 0.011, in CF and from 6.8 (0.5) to 7.7 (1.4), p = 0.004, in controls. Moment ratio and Scond similarly increased. While change in VI indices was heterogeneous in individuals, decrease in functional residual capacity was most strongly associated with LCI increase.ConclusionMBW protocols strongly influence measures of VI. The 1 L VT MBW protocol leads to overestimation of VI and is not recommended in children.