Table 8– Single-breath washout (SBW) measurement quality control
Testing position: seated position for all subjects
 In general SBW only feasible in older children and adults ≥12 yrs
 Nose clip and maintain a tight mouthpiece seal
Three technically acceptable SBW runs should be performed, with acceptability defined by the following criteria
 Within-test criteria
  No evidence of leak (as described for MBW)
  Inspiratory and expiratory flow maintained between 400 and 500 mL·s−1 over first three-quarters of inspiratory and expiratory portions of test manoeuvre
   Maintaining these flows at end of manoeuvre may be difficult
   Flow restrictors may be useful to maintain desired flow range
  Phase III slope default settings to 25–75% of expired volume
   Manually adjustable to ensure freedom from contamination by phase II, phase IV, and stochastic variations in SIII caused by low frequency noise or cardiogenic oscillations
  Specific to classical VC SBW manoeuvre
   Inspiratory and expiratory VC breaths within 10% within same test
  Specific to modified SBW manoeuvre
   Stable end expiratory level prior to starting the manoeuvre
    Deviation in end-expiratory lung volume at start of the test within 10% of mean VT of preceding five breaths
   Inspiratory volume above FRC reaches 1 L within±10%
 Between-test criteria
  Specific to classical VC manoeuvre
  Expiratory VC values within 10% of highest value
  Specific to modified SBW manoeuvre
   Inspiratory volumes within 10% of 1 L
   Expiratory volumes within 10% of each other
  Re-establish baseline inert gas concentration before starting next test
   N2 SBW: end-tidal N2 concentration returns to baseline levels
   Exogenous SBW: end-tidal inert gas concentration <1/40 of inspired inert gas concentration
  Sufficient interval between tests of at least two minutes to stabilise volume history and to reset alveolar N2 concentrations
Test equipment and performance must adhere to infection control guidelines
  • MBW: multiple-breath washout; SIII: phase III slope; VC: vital capacity; VT: tidal volume; FRC: functional residual capacity; N2: nitrogen gas.