Predicting long-term mortality with two different criteria of exercise-induced desaturation in COPD

Background: There are few reports on exercise-induced desaturation (EID) as a predictor of mortality in chronic obstructive pulmonary disease (COPD). However, the definitions of EID vary in published reports. The main purpose was to evaluate the association between EID and long-term mortality by applying two criteria of EID. Methods: A total of 507 subjects were selected from the Korean Obstructive Lung Disease cohort. EID was assessed using the 6-min walk test (6MWT) and defined using two different criteria [1]: post-6MWT oxygen saturation (SpO(2)) of <= 88% (criterion A) and [2] post-6MWT SpO(2) < 90% or a decrease of >= 4% compared to baseline (criterion B). Results: The prevalence of EID was 5.1% based on criterion A and 13.0% based on criterion B. Regardless of the criteria used, mortality was higher in the EID group than in the non-EID group (A: 50 vs. 11.4%, B: 33.3 vs. 10.4%) during up to 161 months of follow-up. COPD patients without EID survived significantly longer than those with EID (A: 143.5 vs. 92.9, B: 144.8 vs. 115.2 months). Multivariate Cox regression analysis revealed that COPD patients with EID had a 2.4-fold increased risk of death by criterion A (adjusted HR 2.375; 95% CI: 1.217-4.637; P = 0.011). The risk of death increased in COPD patients with EID by criterion B, but the difference was not statistically significant. Conclusions: COPD patients with EID demonstrated significantly higher long-term mortality than those without EID. The EID criterion A has a better predictive value for mortality in COPD.