Table 4– Recommendations for online washout software
Software to display flow, volume and respiratory rate monitoring are essential for both fixed breathing protocols (SBW and MBW in adults and older adolescents) and to monitor and stabilise tidal breathing in younger subjects
 Volume time series display of BTPS adjusted data should be of sufficient length and size to detect volume drift
  Differentiating technical causes from physiological causes of volume drift may be difficult
  Sudden step changes in volume may indicate leak
Graphical display of inert gas concentration traces both during the wash-in and washout phases
 To assess suitability of timing to start the washout phase
 To monitor for leaks (see table 5), this should include a clear display of the “zero” inert gas baseline concentration level, which may not be achieved in cases such as insufficient washout as supply or leak; if an automated correction of deviation from zero baseline is performed by the software, the magnitude of this deviation correction must be clearly visible to alert the user
Accurate breath detection of start and end of inspiration and expiration adhering to existing standards for identification of tidal breaths [32, 33]; these standards were developed for infants but are extendable for application in adults
 Distinguishing start and end of inspirations and expirations from minor fluctuations in flow during pauses and irregular breathing is usually accomplished using flow thresholds but a combination of flow and volume based criteria may be better
Accurate detection of end-tidal inert gas concentration
 Average over 5–10 samples (or 25–50 ms), ending five samples (or 25 ms) before the end of expiration (see section E4.1 in the online supplementary data)
 Alternatively average over 95–98% of the expired volume
If SnIII progression is being measured then display the breath-by-breath inert gas expirogram to allow the user to ensure sufficient SIII is visible (≥50% of the expired VT)
To aid the user in determining when end-of-test thresholds are met, online analysis should display
 End-tidal inert gas concentration
 If SnIII progression or moment ratios are being measured: FRC and lung turnover (CEV/FRC for each breath) as the washout proceeds
To limit the time required for testing, automated calculation of the following indices should occur at the end of each test
 Breath-by-breath calculation and display of VD,aw (quality control for leak detection)
Global ventilation distribution indices
Offline analysis and quality control can then be performed as required by the operator (as detailed in the section entitled Validation of washout equipment)
Warning messages should inform the operator when important quality control steps have not been fulfilled
  • SBW: single-breath washout; MBW: multiple-breath washout; BTPS: body temperature, ambient pressure, saturated with water; SnIII: normalised phase III slope; VT: tidal volume; CEV: cumulative expired volume; FRC: functional residual capacity; VD,aw: deadspace volume of the conducting airways.