Interpretation of treatment changes in 6-minute walk distance in patients with COPD

Abstract

There is uncertainty about the interpretation of changes in the 6-min walk distance (6MWD) in chronic obstructive pulmonary disease (COPD) patients and whether the minimal important difference (MID) for this useful outcome measure exists.Data were used from nine trials enrolling a wide spectrum of COPD patients with 6MWD at baseline and follow-up and used to determine threshold values for important changes in 6MWD using three distribution-based methods. Anchor-based methods to determine a MID were also evaluated.Data were included of 460 COPD patients with a mean¡SD forced expiratory volume in one second (FEV1) of 39.2¡14.1% predicted and 6MWD of 361¡112 m at baseline. Threshold values for important effects in 6MWD were between 29 and 42 m, respectively, using the empirical rule effect size and the standardised response mean. The threshold value was 35 m (95% confidence interval 30-42 m) based on the standard error of measurement. Correlations of 6MWD with patient-reported anchors were too low to provide meaningful MID estimates.6-min walk distance should change by ,35 m for patients with moderate to severe chronic obstructive pulmonary disease in order to represent an important effect. This corresponds to a 10% change of baseline 6-min walk distance. The low correlations of 6-min walk distance with patient-reported anchors question whether a minimal important difference exists for the 6-min walk distance.

Prospective validation of the endurance shuttle walking test in the context of bronchodilation in COPD

“…In this context, some authors have suggested that correlation coefficients of the relationship should be o0.5 for interpreting anchor-based approaches results satisfactorily. In the case of correlation coefficients between 0.3 and 0.5, the analyses can be performed but the interpretation of the results and estimates requires some caution [26,28]. With correlation coefficients amounting to 0.48 and 0.45 for endurance time and endurance distance, respectively, and considering the present estimates are very similar to what was previously reported, we are confident about the validity of the proposed estimates.…”

“…As previously suggested [13,25,26], different methods should be combined for the determination of MID values, considering that there is no consensus in favour of a single best methodology for the determination of MID estimate and that this estimate should be viewed as a range of probable values rather than as a discrete value.…”

Three-year follow-up study of respiratory and systemic manifestations of chronic obstructive pulmonary disease

“…According to the values proposed by different investigators (19,20), 31 patients (32%) presented clinically significant worsening (≥54 m) and in 36 patients (38%) the decrease in 6MWD was ≥35 m. The proportion of patients with a minimum clinically significant decline ranged from 50 to 58% among patients with severe or very severe disease. The Charlson index increased significantly during the study period [3 (3-4) vs 4 (3-5); P = 0.009].…”

“…The distance covered is reported in meters. There are two different references to define the minimum clinically significant decline in 6MWD (19,20): a reduction ≥54 m (19) or ≥35 m (20) from baseline. In this study, we evaluated the 6MWD decline according to both definitions.…”

Effects of inpatient pulmonary rehabilitation in patients with interstitial lung disease

“…In COPD patients a distance of 54 m has been identified for the MCID, although more recently this value has been questioned and the threshold for MCID may be lower in this group (PUHAN et al [26] suggest 35 m) [27]. Based on a large cohort of 822 IPF patients the MCID for the 6MWD was calculated to be 24-45 m, depending on the statistical method employed [28].…”