title: Is hypercapnia associated with poor prognosis in chronic obstructive pulmonary disease? A long-term follow-up cohort study.
abstract: OBJECTIVE
  To assess whether hypercapnia may predict the prognosis in chronic obstructive pulmonary disease (COPD).
  
  
  METHODS
  Prospective cohort study comparing the survival of patients with COPD and normocapnia to those with chronic hypercapnia.
  
  
  METHODS
  Patients with consecutive COPD were enrolled between 1 May 1993 and 31 October 2006 at two medical centres. Follow-up was censored on 31 October 2011.
  
  
  METHODS
  A total of 275 patients with stable COPD and aged 40-85 years were enrolled. Diagnosis of hypercapnia was confirmed by blood gas analysis. Patients with near-terminal illness or comorbidities that affect PaCO2 (obstructive sleep apnoea, obesity-related hypoventilation, or neuromuscular disease) were excluded. The outcome of 98 patients with normocapnia and 177 with chronic hypercapnia was analysed.
  
  
  METHODS
  Overall survival.
  
  
  RESULTS
  Median survival was longer in patients with normocapnia than in those with hypercapnia (6.5 vs 5.0 years, p=0.016). Multivariate COX regression analysis indicated that age (HR=1.043, 95% CI 1.012 to 1.076), Charlson Index, which is a measure of comorbidity (HR=1.172, 95% CI 1.067 to 1.288), use of medication (HR=0.565, 95% CI 0.379 to 0.842), body mass index (BMI) (HR=0.922, 95% CI 0.883 to 0.963), PaCO2 (HR=1.026, 95% CI 1.011 to 1.042), Cor pulmonale (HR=2.164, 95% CI 1.557 to 3.006), non-invasive positive-pressure ventilation (NPPV) (HR=0.615, 95% CI 0.429 to 0.881) and per cent of forced expiratory volume in 1 s (FEV1%) (HR=0.979, 95% CI 0.967 to 0.991), were independent risk factors for mortality.
  
  
  CONCLUSIONS
  Increased age, Charlson Index, chronic hypercapnia and Cor pulmonale, and decreased FEV1%, use of medication, BMI and NPPV, were associated with a poor prognosis in patients with COPD.
authors.affiliation: Department of Respiratory and Critical Care Medicine, Beijing Institute of Respiratory Medicine, Beijing Chao-Yang Hospital Beijing, Capital Medical University, Beijing, China Department of Respiratory and Critical Care Medicine, Shou-Gang Hospital Affiliated to Peking University, Beijing, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Yang
authors.affiliation: Department of Respiratory and Critical Care Medicine, Shou-Gang Hospital Affiliated to Peking University, Beijing, China.
authors.forename: Pingchao
authors.initials: P
authors.lastname: Xiang
authors.affiliation: Department of Respiratory and Critical Care Medicine, Shou-Gang Hospital Affiliated to Peking University, Beijing, China.
authors.forename: Erming
authors.initials: E
authors.lastname: Zhang
authors.affiliation: Department of Respiratory and Critical Care Medicine, Shou-Gang Hospital Affiliated to Peking University, Beijing, China.
authors.forename: Weian
authors.initials: W
authors.lastname: Guo
authors.affiliation: Department of Respiratory and Critical Care Medicine, Shou-Gang Hospital Affiliated to Peking University, Beijing, China.
authors.forename: Yanwei
authors.initials: Y
authors.lastname: Shi
authors.affiliation: Department of Respiratory and Critical Care Medicine, Shou-Gang Hospital Affiliated to Peking University, Beijing, China.
authors.forename: Shuo
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Department of Respiratory and Critical Care Medicine, Beijing Institute of Respiratory Medicine, Beijing Chao-Yang Hospital Beijing, Capital Medical University, Beijing, China.
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Tong
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D006935:Hypercapnia / Q000175:diagnosis / Q000209:etiology*; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D016016:Proportional Hazards Models; D011446:Prospective Studies; D029424:Pulmonary Disease, Chronic Obstructive / Q000150:complications / Q000175:diagnosis* / Q000401:mortality; D012307:Risk Factors; D015996:Survival Rate
keywords: QUALITATIVE RESEARCH