Predictive Significance of the Six-Minute Walk Distance for Long-Term Survival in Chronic Hypercapnic Respiratory Failure

Abstract

Background: The 6-min walk distance (6-MWD) is a global marker of functional capacity and prognosis in chronic obstructive pulmonary disease (COPD), but less explored in other chronic respiratory diseases. Objective: To study the role of 6-MWD in chronic hypercapnic respiratory failure (CHRF). Methods: In 424 stable patients with CHRF and non-invasive ventilation (NIV) comprising COPD (n = 197), restrictive diseases (RD; n = 112) and obesity-hypoventilation-syndrome (OHS; n = 115), the prognostic value of 6-MWD for long-term survival was assessed in relation to that of body mass index (BMI), lung function, respiratory muscle function and laboratory parameters. Results: 6-MWD was reduced in patients with COPD (median 280 m; quartiles 204/350 m) and RD (290 m; 204/362 m) compared to OHS (360 m; 275/440 m; p < 0.001 each). Overall mortality during 24.9 (13.1/40.5) months was 22.9%. In the 424 patients with CHRF, 6-MWD independently predicted mortality in addition to BMI, leukocytes and forced expiratory volume in 1 s (p < 0.05 each). In COPD, 6-MWD was strongly associated with mortality using the median [p < 0.001, hazard ratio (HR) = 3.75, 95% confidence interval (CI): 2.24–6.38] or quartiles as cutoff levels. In contrast, 6-MWD was only significantly associated with impaired survival in RD patients when it was reduced to 204 m or less (1st quartile; p = 0.003, HR = 3.31, 95% CI: 1.73–14.10), while in OHS 6-MWD had not any prognostic value. Conclusions: In patients with CHRF and NIV, 6-MWD was predictive for long-term survival particularly in COPD. In RD only severely reduced 6-MWD predicted mortality, while in OHS 6-MWD was relatively high and had no prognostic value. These results support a disease-specific use of 6-MWD in the routine assessment of patients with CHRF.

The 6-Minute Walk Test in Chronic Respiratory Failure: Does Observed or Predicted Walk Distance Better Reflect Patient Functional Status?

“…The authors calculated the percent-of-predicted 6MWD, but they did not use them for analysis. 7 In the present study, although the majority of the subjects had mildly less hypercapnic and hypoxemic ABG values and worse spirometry results, especially in OHS, they were more or less similar to the patients presented in the Budweiser report. Our study had higher 6MWD and predicted values.…”

“…[3][4][5][6] Actual 6MWD was also studied in chronic hypercapnic respiratory failure patients who were using home noninvasive ventilation (NIV). 7 Budweiser et al found a similar hazard ratio for mortality for the actual 6MWD and percent-of-predicted 6MWD in 424 patients with chronic hypercapnic respiratory failure using home NIV. 7 However, they did not study the relationship between pulmonary function and actual 6MWD versus percent-of-predicted 6MWD.…”

“…8 They mainly assessed long-term survival and suggested a disease-specific use of 6MWD to assess and monitor NIV-treated subjects with chronic hypercapnic respiratory failure. 7 They evaluated the 6MWD as a predictor of long-term survival for COPD (n ϭ 197), restrictive lung disease (n ϭ 112), and OHS (n ϭ 115). Their results may be relevant to COPD, but have limited value for restrictive lung diseases.…”

“…Our study had higher 6MWD and predicted values. 7 Age is an important determinant of 6MWD, and in many studies patients are included only when age is greater than 20 years or between 20 -50 or 40 -85 years. 9,10,[23][24][25] In the present study the majority of subjects were in their sixth decade, and the range was 32-85 years.…”

“…These characteristics were similar to those of the Budweiser study. 7 Enright and Sherrill used all parameters for calculating reference values for 6MWD and cautioned using these with non-white patients and those younger than 40 or older than 80 years. 8 Previous studies have shown that predicted FEV 1 is highly correlated with 6MWD in patients with COPD, especially when FEV 1 is Ͻ 35%.…”