title: Hypo- and hypercapnia predict mortality in oxygen-dependent chronic obstructive pulmonary disease: a population-based prospective study.
abstract: BACKGROUND
  The prognostic role of the arterial blood gas tension of carbon dioxide (PaCO2) in severe Chronic Obstructive Pulmonary Disease (COPD) remains unknown. The aim of this study was to estimate the association between PaCO2 and mortality in oxygen-dependent COPD.
  
  
  METHODS
  National prospective study of patients starting long-term oxygen therapy (LTOT) for COPD in Sweden between October 1, 2005 and June 30, 2009, with all-cause mortality as endpoint. The association between PaCO2 while breathing air, PaCO2 (air), and mortality was estimated using Cox regression adjusted for age, sex, arterial blood gas tension of oxygen (PaO2), World Health Organization performance status, body mass index, comorbidity, and medications.
  
  
  RESULTS
  Of 2,249 patients included, 1,129 (50%) died during a median 1.1 years (IQR 0.6-2.0 years) of observation. No patient was lost to follow-up. PaCO2 (air) independently predicted adjusted mortality (p < 0.001). The association with mortality was U-shaped, with the lowest mortality at approximately PaCO2 (air) 6.5 kPa and increased mortality at PaCO2 (air) below 5.0 kPa and above 7.0 kPa.
  
  
  CONCLUSIONS
  In oxygen-dependent COPD, PaCO2 (air) is an independent prognostic factor with a U-shaped association with mortality.
authors.affiliation: Department of Medicine, Blekinge Hospital, 37185 Karlskrona, Sweden. zai.ahmd@gmail.com.
authors.forename: Zainab
authors.initials: Z
authors.lastname: Ahmadi
authors.forename: Anna
authors.initials: A
authors.lastname: Bornefalk-Hermansson
authors.forename: Karl A
authors.initials: KA
authors.lastname: Franklin
authors.forename: Bengt
authors.initials: B
authors.lastname: Midgren
authors.forename: Magnus P
authors.initials: MP
authors.lastname: Ekström
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D006935:Hypercapnia / Q000175:diagnosis / Q000401:mortality* / Q000628:therapy; D016857:Hypocapnia / Q000175:diagnosis / Q000401:mortality* / Q000628:therapy; D008297:Male; D010102:Oxygen Inhalation Therapy / Q000009:adverse effects / Q000401:mortality*; D011159:Population Surveillance / Q000379:methods; D011237:Predictive Value of Tests; D011446:Prospective Studies; D029424:Pulmonary Disease, Chronic Obstructive / Q000175:diagnosis / Q000401:mortality* / Q000628:therapy; D012042:Registries; D013548:Sweden / Q000453:epidemiology