Effects of using a mask vs mouthpiece on the multiple breath inert gas washout technique

Abstract

Multi-breath washout (MBW) measurement in older children and adults is performed using a mouthpiece(MP) interface. Masks are better tolerated by younger children but increase equipment deadspace. We examined the effect of mask vs MP on functional residual capacity(FRC) and lung clearance index(LCI) from MBW. Method: The study design incorporated repeated measures and interface comparison. Healthy adults were randomised to either “Mask-MP-MP” or “MP-MP-Mask” protocols, with each MBW performed in triplicate, and 5 mins between sets. Measurements were by mass spectrometer (Aurora 2005 AJRCCM). Paired t-tests with 95% limits of agreement assessed repeatability(MP1 vs MP2) and any differences between Mask vs MP. Research ethics approval and consent were obtained. Results: Technically acceptable data were obtained in 14 adults (36%males; age:22-56y). Respiratory rate and tidal volume were similar using either approach. Repeatability: Both FRC and LCI were repeatable using the MP[(Mean(95%CI)diff: FRC:0.012L(-0.1;0.1); LCI:-0.1(-0.3;0.1)]. Mask vs MP: FRC and LCI were both significantly higher when assessments were made using a mask compared with a MP[FRC:0.101L(0;0.2);LCI;0.4(0.2;0.7)]. Conclusion: The increase in LCI when using a mask exceeded normal within test variability in adults and could influence interpretation of results especially if different patient interfaces are used when collecting data in younger children.