Repeated desaturation in 6 minute walk test increases risk for mortality in COPD patients

Background: Whether patients who desaturate during repeated 6 minute walk tests (6MWT) over time have higher risk of death is unknown. Aim: To examine associations between mortality and desaturation in repeated 6MWTs. Methods: 370 COPD patients, 40-76yrs, in the Bergen COPD Cohort study 2006-10, performed 6MWT at baseline. 307 performed a new 6MWT 1 yr later. Oxygen saturation (SpO2) was measured before and after the test. Desaturation was defined as a 4% reduction between pre- and post-test SpO2, and a post-test SpO2<90%. Information on all-cause and respiratory mortality was collected from a national registry in 2015. Multivariate Cox regression analysis of mortality was performed adjusting for baseline values of sex, age, body composition (cachectic, normal, obese), smoking, FEV1 % predicted, resting arterial oxygen tension, number of exacerbations the last yr before inclusion, Charlson comorbidity score, and walking distance in the 6MWT. Results: 23% of the patients desaturated at baseline 6MWT. One yr later 32% of the patients desaturated, 19% desaturated in both tests. 123 patients died before 2015; 59 due to respiratory causes. A significant increased risk of respiratory mortality was associated with desaturating in both tests (HR 4.3 (95%CI 1.6, 11.9)) compared with no desaturation. Desaturating only at follow-up were not associated with respiratory mortality (HR 1.4 (95%CI 0.5, 5.3). There was a borderline significant association with all-cause mortality and desaturation at both tests. Conclusion: Repeated desaturation in the 6MWT increased the risk for respiratory mortality. Measuring desaturation at repeated 6MWTs could help identify COPD patients with severe prognosis.