Reproducibility of the 6-minute walk test for ambulatory oxygen prescription.

BACKGROUND: Ambulatory oxygen is frequently prescribed for patients with chronic obstructive pulmonary disease (COPD) who have oxygen desaturation </=88% during exercise. The 6-min walk test (6MWT) with continuous pulse oximetry monitoring is a common method to document this oxygen desaturation, but the reproducibility of this test in determining the need for ambulatory oxygen in patients with COPD is not well documented.

OBJECTIVE: The aim of this study was to establish the reproducibility of the 6MWT in determining the need for ambulatory oxygen prescription in stable COPD patients using the Centers for Medicare and Medicaid (CMS) criteria for ambulatory oxygen prescription.

METHODS: The study was designed as a prospective observational study in an academic health center and associated pulmonary rehabilitation program. Eighty-eight COPD patients referred to pulmonary rehabilitation underwent continuous pulse oximetry while performing standard 6MWT on 3 separate days.

RESULTS: Fifty-one (58%) of these patients desaturated by continuous pulse oximetry to an SpO(2) < or = 88% on a least one of the 6MWTs. Only 26 patients (30%) demonstrated consistency in meeting the criteria for ambulatory oxygen set forth by the CMS on all three 6MWT with a kappa statistic of 0.62. The percent agreement between 6MWTs for ambulatory oxygen prescription was 72% and the paired observation was 51%.

CONCLUSIONS: The 6MWT distance is simple and widely used as a consistent measure of functional capacity in patients with COPD; however, the 6MWT oxygen saturation has only modest reproducibility in determining the need for ambulatory oxygen in stable COPD patients undergoing pulmonary rehabilitation.