Shorter walk test durations to detect ambulatory oxygen desaturation in interstitial lung disease: an observational cohort study

Abstract

Introduction6-Minute Walk Test (6MWT) oxygen desaturation is an indication for ambulatory oxygen therapy (AOT) (British Thoracic Society (BTS) SpO2<90%; American Thoracic Society (ATS) SpO2≤ 88%). Shorter walk test durations may be beneficial in remote monitoring or in severe lung disease (ILD), where completing a 6MWT is challenging.MethodsRetrospective routine clinical 6MWT with minute interval SpO2%, lung function and mortality data were collected from patients with ILD. Median lowest SpO2% at different time periods of the 6MWT were compared statistically and prognostically. Patients were classified by Distance-Oxygen-Gender-Age-Physiology (DO-GAP) index.Results274 patient records were analysed. Median SpO2% recorded at 0–1, 1–2, 2–3, 3–4, 4–5 and 5–6 min of the 6MWT were 96%, 93%, 92%, 92%, 91.5% and 91%, respectively (p<0.001). Prognostically, areas under the curve (AUC) for predicting 3-year mortality were significant (p<0.001) and similar for the minimum SpO2% between 0–1, 1–2, 2–3, 3–4, 4–5 and 5–6 min (AUC=0.71, 0.76, 0.77, 0.76, 0.77, 0.76, respectively). 111 patients desaturated to <90% (BTS criteria) during the 6MWT, with the median time to desaturation ranging from 1.5–2.5 min between DO-GAP groups (p=0.01). 94 patients desaturated to ≤88% (ATS criteria) during the 6MWT, with the median time to desaturation ranging from 1.5–2.2 min between DO-GAP groups.ConclusionExertional desaturation manifests during earlier stages of the 6MWT. A 3-minute walk has 87–91% sensitivity in detecting oxygen desaturation requiring AOT, whilst retaining prognostic value. Shorter walk durations can efficiently detect desaturation in ILD, making it more patient-centred and feasible for remote testing.