Chest
Volume 127, Issue 6, June 2005, Pages 1904-1910
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Clinical Investigations
Survival of Chronic Hypercapnic COPD Patients Is Predicted by Smoking Habits, Comorbidity, and Hypoxemia

https://doi.org/10.1378/chest.127.6.1904Get rights and content

Study objectives

Chronic hypercapnia in patients with COPD has been associated with a poor prognosis. We hypothesized that, within this group of chronic hypercapnic COPD patients, factors that could mediate this hypercapnia, such as decreased maximum inspiratory mouth pressure (Pimax), decreased maximum expiratory mouth pressure (Pemax), and low hypercapnic ventilatory response (HCVR), could be related to survival. Other parameters, such as arterial blood gas values, airway obstruction (FEV1), body mass index (BMI), current smoking status, and the presence of comorbidity were studied as well.

Methods

A cohort of 47 chronic hypercapnic COPD patients recruited for short-term trials (1 to 3 weeks) in our institute was followed up for 3.8 years on average. Survival was analyzed using a Cox proportional hazards model. The risk factors considered were analyzed, optimally adjusted for age and gender.

Results

At the time of analysis 18 patients (10 male) were deceased. After adjusting for age and gender, Pimax, Pemax, and HCVR were not correlated with survival within this hypercapnic group. Current smoking (hazard ratio [HR], 7.0; 95% confidence interval [CI], 1.4 to 35.3) and the presence of comorbidity (HR, 5.5; 95% CI, 1.7 to 18.7) were associated with increased mortality. A higher Pao2 affected survival positively (HR, 0.6 per 5 mm Hg; 95% CI, 0.4 to 1.0). Paco2 tended to be lower in survivors, but this did not reach statistical significance (HR, 2.0 per 5 mm Hg; 95% CI, 0.9 to 4.3). FEV1 and BMI were not significantly related with survival in hypercapnic COPD patients.

Conclusion

In patients with chronic hypercapnia, only smoking status, the presence of comorbidity, and Pao2 level are significantly associated with survival. Airway obstruction, age, and BMI are known to be predictors of survival in COPD patients in general. However, these parameters do not seem to significantly affect survival once chronic hypercapnia has developed.

Section snippets

Study Population

A cohort of 47 chronic hypercapnic COPD patients (28 male; mean age, 66.3 ± 6.7 years [± SD]) recruited for other trials, of 1 to 3 weeks in duration, in our institute between January 1996 and February 2000 was prospectively followed up, yielding 178.8 person-years in total.293031 Follow-up time ranged from 3.1 to 7.1 years among survivors.

COPD was defined according to the standards of the American Thoracic Society.17 Chronic hypercapnia was defined as Paco2 > 45.0 mm Hg recorded twice with an

Results

At the time of analysis, 18 deaths had occurred (10 male patients) in 47 chronic hypercapnic subjects, contributing in total 178.8 person-years of follow-up. Thus, the overall survival rate after 3.8 years was 61.7%. Ten subjects (55.6%) died of acute-on-chronic respiratory failure triggered by an acute exacerbation of COPD (n = 9) or pneumonia (n = 1). Two subjects (11.1%) died of the consequences of late-stage lung cancer. The others died of unknown causes.

Our group of subjects consisted of

Discussion

Respiratory muscle strength and HCVR were not related to the prognosis of chronic hypercapnic COPD patients. Current smoking, the presence of comorbidity, and the level of hypoxemia, however, did predict survival in these patients.

Respiratory muscle weakness in COPD patients causes hypoventilation with subsequent hypercapnia and hypoxemia. Hypercapnia is regarded a poor prognostic indicator in COPD patients in general.1926 We hypothesized that within the subgroup of hypercapnic COPD patients,

Acknowledgment

The authors thank Drs. F. Brijker and M. Wagenaar for assistance in conducting this study.

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