Chest
Volume 134, Issue 4, October 2008, Pages 746-752
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Original Research
COPD
Distance and Oxygen Desaturation During the 6-min Walk Test as Predictors of Long-term Mortality in Patients With COPD

https://doi.org/10.1378/chest.08-0520Get rights and content

Rationale

The distance walked in the 6-min walk test (6MWT) predicts mortality in patients with severe COPD. Little is known about its prognostic value in patients with a wider range of COPD severity, living in different countries, and the potential additional impact of oxygen desaturation measured during the test.

Methods

We enrolled 576 stable COPD outpatients in Spain and the United States and observed them for at least 3 years (median, 60 months). We measured FEV1, body mass index, Pao2, Charlson comorbidity score, 6-min walk distance (6MWD), and oxygen saturation by pulse oximetry (Spo2) during the 6MWT. Desaturation was defined as a fall in Spo2 ≥ 4% or Spo2 < 90%. Regression analysis helped determine the association between these variables and all-cause and respiratory mortality.

Results

The 6MWD was a good predictor of all-cause and respiratory mortality primarily in patients with FEV1 < 50% of predicted (p < 0.001) after adjusting for all covariates. Patients with desaturation during the 6MWT had a higher mortality rate than patients without desaturation (67% vs 38%, p < 0.001). Oxygen desaturation predicted mortality (relative risk, 2.63; 95% confidence interval, 1.53 to 4.51; p < 0.001) but with less power than Pao2 at rest.

Conclusions

The 6MWD helps predict mortality primarily in patients with severe COPD. Although the oxygen desaturation profile during the 6MWT improves the predictive ability of the 6MWD, it appears to be of less relevance than in other lung diseases and than the resting Pao2.

Section snippets

Materials and Methods

A total of 576 outpatients with COPD and wide range of airflow obstruction from clinics in the United States (Bay Pines VA Medical Center, Bay Pines, FL, and Caritas St. Elizabeth's Medical Center, Boston, MA) and Spain (Hospital Universitario La Candelaria, Tenerife, and Hospital Miguel Servet, Zaragoza, Spain) participated in the study, which was approved by the human review boards at each center. Patients were enrolled from December 1995 and were followed up until January 2006. This is part

Results

The cohort of all patients screened and the patients included in the study with the different subgroup analysis are presented in Figure 1. The 576 patients included were distributed as follows: 323 patients (56%) were from the United States (226 from St. Petersburg, FL, and 97 from Boston, MA) and 253 patients (44%) were from Spain (118 from Tenerife and 135 from Zaragoza). Median age was 68 years (range, 51 to 81 years), and most (89%) were men. At entry time using the ATS-ERS/Global

Discussion

This study presents two novel findings. First, it demonstrates for the first time that in patients with a wide range of airflow obstruction the 6MWD is an important prognostic factor primarily in patients with severe COPD (FEV1 < 50% of predicted). Secondly, our study showed that oxygen desaturation during the 6MWD may have a possible small additive role to the distance walked in helping predict mortality but is not as useful as the determination of the Pao2.

The new guidelines for COPD

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    The authors have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

    Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/misc/reprints.shtml).

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