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Distance and Oxygen Desaturation During the 6-min Walk Test as Predictors of Long-term Mortality in Patients With COPD

*From the Pulmonary Department (Dr. Casanova) and Research Unit (Drs. de Torres and Aguirre-Jaíme), Hospital La Candelaria, Tenerife, and Pulmonary Department (Dr. Marin), Hospital Miguel Servet, Zaragoza, Spain; Pulmonary Division (Dr. Cote), Bay Pines VA Medical Center, St. Petersburg, FL; and Pulmonary Division (Drs. Pinto-Plata, Vassaux, and Celli). Caritas-St. Elizabeth's Medical Center, Boston, MA.

Correspondence to: Ciro Casanova, MD, Associate Professor Universidad de La Laguna, Tenerife, Respiratory Research Unit, Pulmonary Department, Hospital Universitario La Candelaria, Carretera del Rosario n° 145, 38010- Santa Cruz de Tenerife, Spain; e-mail: ccasanova{at}canarias.org

Abstract

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.

Key Words: COPD • long-term mortality • 6-min walk test

Abbreviations: ATS, American Thoracic Society • BMI, body mass index • BODE, body mass index, airflow obstruction, dyspnea, exercise performance • CI, confidence interval • ERS, European Respiratory Society • 6MWD, 6-min walk distance • 6MWT, 6-min walk test • RR, relative risk • Spo₂, oxygen saturation by pulse oximetry