Continuous Monitoring of Pulse Oximetry During the 6-Minute Walk Test Improves Clinical Outcomes Prediction in COPD

BACKGROUND: Continuous monitoring of SpO2 throughout the 6-min walk test (6MWT) unveiled that some patients with respiratory diseases may present values across the test lower than SpO2 measured at the end of the test. Nevertheless, it remains unclear whether this approach improves the yield of walk-induced desaturation detection in predicting mortality and hospitalizations in patients with COPD. METHODS: Four hundred twenty-one subjects (51% males) with mild−very severe COPD underwent a 6MWT with continuous measurement of SpO2. Exercise desaturation was defined as a fall in SpO2 ≥ 4%. All-cause mortality was assessed up to 6 y of follow-up and the rate of hospitalizations in the year succeeding the 6MWT. RESULTS: One hundred forty-nine subjects (35.4%) died during a mean (interquartile) follow-up of 55.5 (30.2−64.1) months. Desaturation was observed in 299/421 (71.0%). SpO2 along the test was < end SpO2 (88 [82−92]% vs 90 [84−93]%, P < .001). Desaturation detected only during (but not at the end of) the test was found in 81/421 (19.2%) participants. Multivariate Cox regression model adjusted for sex, body composition, FEV1, residual volume/total lung capacity ratio, walk distance, O2 supplementation during the test, and comorbidities retained the presence of desaturation either at the end (1.85 [95% CI 1.02−3.36]) or only along the test (2.08 [95% CI 1.09−4.01]) as significant predictors of mortality. The rate of hospitalizations was higher in those presenting with any kind of desaturation compared to those without exercise desaturation. Logistic regression analysis revealed that walking interruption and diffusing capacity of the lung for carbon monoxide predicted desaturation observed only during the test. CONCLUSIONS: O2 desaturation missed by end-exercise SpO2 but exposed by measurements during the test was independently associated with all-cause mortality and hospitalizations in subjects with COPD.