Consensus statement on inert gas washout measurement: at the threshold of clinical use.

I nert gas washout tests including single breath washout (SBW) and multiple breath washout (MBW) have been used for several decades across a wide age range spanning from early infancy to late adulthood. In the past, these lung function tests were typically applied in research settings, assessing lung volume and ventilation distribution in order to gain insight into presence, severity and progression of a multitude of diseases, such as chronic lung disease of infancy [1–4], cystic fibrosis [5–9], asthma [10–12] and chronic obstructive pulmonary disease [13–15]. Importantly, inert gas washout detects poor ventilation distribution in the presence of normal spirometry [16]. Until recently, inert gas washout testing was characterised by highly specific and at times incompletely validated hardware environments, customised software for data acquisition and analysis, and a general lack of consensus on criteria for processing and quality control of washouts across age groups. Thus, comparison and generalisability of study results from different laboratories testing patients with different diseases at different ages was extremely difficult. In this issue of the European Respiratory Journal, an international expert group of the European Respiratory Society (ERS) and American Thoracic Society (ATS) takes an important step forward towards overcoming some of the most demanding issues, by publishing a comprehensive statement on inert gas washout measurements [17].