Short-term Effects of Supplemental Oxygen on 6-Min Walk Test Outcomes in Patients With COPD A Randomized, Placebo-Controlled, Single-blind, Crossover Trial

Abstract

BACKGROUND: The acute effect of supplemental oxygen during exercise has been shown to differ largely among patients with COPD. It is unknown what factors influence oxygen response. METHODS: In a randomized, single-blind fashion, 124 patients with COPD underwent one 6-min walk test on supplemental oxygen (6MWT(O2)) and one 6-min walk test on room air after a practice 6-min walk test. Both gases were delivered via standard nasal prongs (2 L/min). For analyses, patients were stratified on the basis of PaO2 values and compared: (1) 34 patients with resting hypoxemia (HYX); (2) 43 patients with exercise-induced hypoxemia (EIH); and (3) 31 patients with normoxemia (NOX). RESULTS: Oxygen supplementation resulted in an increase in the 6-min walk distance in the total cohort (27 +/- 42 meters; P < .001) and in the subgroups of HYX (37 +/- 40 meters; P < .001) and EIH (28 +/- 44 meters; P < .001) but not in the NOX subgroup (15 +/- 43 meters; P = .065). Forty-two percent of patients with HYX and 47% of patients with EIH improved their 6-min walk distance to a clinically relevant extent (>= 30 meters) by using oxygen. These oxygen responders were characterized by significantly lower 6-min walk distance using room air compared with patients without a relevant response (306 +/- 106 meters vs 358 +/- 113 meters; P < .05). Although oxygen saturation was significantly higher during 6MWT(O2) compared with the 6-min walk test on roomair in all 3 subgroups, it dropped to < 88% during 6MWT(O2) in 73.5% of patients with HYX. CONCLUSIONS: In contrast to patients with NOX, patients with HYX and EIH generally benefit from supplemental oxygen by increasing exercise capacity. However, less than one-half of patients reached the threshold of clinically relevant improvements. These oxygen responders were characterized by significantly lower exercise capacity levels.