SpO ₂ recovery time improves prognostic assessment in interstitial lung disease

Introduction Six-minute walk test (6MWT) parameters assess prognosis in interstitial lung disease (ILD). While exercise-induced desaturation and six-minute walk distance (6MWD) are established predictors, the prognostic value of oxygen saturation (SpO 2 ) recovery time is less clear and is not included in current 6MWT risk models like distance-oxygen gender age physiology (DO-GAP) and oxygen flow rate, distance, dyspnoea and saturation (ODDS), Methods 323 ILD patients undergoing 6MWT at Royal Papworth Hospital NHS Foundation Trust were included. SpO 2 recovery time was defined as the time taken for SpO 2 % to return within 2% of baseline following 6MWT. Associations with 1- and 2-year mortality or lung transplantation were assessed using ROC analysis, Kaplan–Meier curves, and Cox regression. Incremental prognostic value was evaluated by adding SpO 2 recovery time to DO-GAP and ODDS models using C-index, AIC, and likelihood ratio testing. Results SpO 2 recovery demonstrated good discrimination for 1- and 2-year outcomes (AUC 0.75 and 0.73). Kaplan–Meier and pairwise analyses showed a graded association between recovery time and outcomes, with significant differences between <90, 90–120, and >120 s, although separation was greatest for >120 s. In multivariable analysis, TLCO (HR 0.94, 95% CI 0.92–0.96, p<0.001), FVC (HR 0.98, 95% CI 0.97–1.00, p=0.028), and SpO 2 recovery >120 s (HR 2.11, 95% CI 1.04–4.29, p=0.039) were independently associated with outcomes. Addition of SpO 2 recovery improved ODDS model performance (p<0.01) and DO-GAP in whole cohort. Conclusions Prolonged SpO 2 recovery time (>120 s) independently predicted outcomes and improved existing developed risk models in ILD.