title: Serial Measurements of Arterial Oxygen Tension are Associated with Mortality in COPD.
abstract: BACKGROUND
  Knowledge on factors associated with mortality can help identify patients with COPD that might benefit from close monitoring and intervention. Arterial blood gases (ABGs) are related to mortality, but both arterial tension of oxygen (PaO2) and arterial tension of carbon dioxide (PaCO2) vary over time. The aim of our study was to investigate the association between repeatedly measured ABGs and mortality in men and women with COPD.
  
  
  METHODS
  A cohort of 419 Norwegian subjects with COPD, GOLD stage II-IV, aged 40-75, was followed up with up to seven ABGs, measured during stable phase for three years. Cox proportional hazard models were used to quantify the relationship between both single and repeatedly measured ABGs and all-cause mortality after five years, adjusting for age, sex, and the updated BODE index.
  
  
  RESULTS
  A total of 64 subjects died during follow-up. Mean initial arterial oxygen tension (standard deviation) was significantly higher in survivors compared to deceased, with PaO2 (in kPa) 9.4 (1.1) versus 8.8 (1.2), p<0.001. Corresponding numbers for PaCO2 were 5.3 (0.5) and 5.5 (0.7), p < 0.001. In analyses adjusting for age, sex, and the updated BODE index hazard ratios - HR(95% confidence intervals) - for all-cause mortality were 0.73 (0.55, 0.97) and 1.58 (0.90, 2.76) for repeated measures of PaO2 and PaCO2, respectively.
  
  
  CONCLUSIONS
  Both arterial oxygen and carbon dioxide tension were related to mortality in this study, and arterial oxygen tension added prognostic information to the updated BODE index in COPD.
authors.affiliation: 1 Department of Medicine, Haukeland University Hospital , Bergen , Norway.
authors.forename: Marianne
authors.initials: M
authors.lastname: Aanerud
authors.forename: Eirunn W
authors.initials: EW
authors.lastname: Saure
authors.forename: Marta
authors.initials: M
authors.lastname: Benet
authors.forename: Xavier
authors.initials: X
authors.lastname: Basagana
authors.forename: Per S
authors.initials: PS
authors.lastname: Bakke
authors.forename: Judith
authors.initials: J
authors.lastname: Garcia-Aymerich
authors.forename: Tomas M L
authors.initials: TM
authors.lastname: Eagan
authors.forename: Josep M
authors.initials: JM
authors.lastname: Anto
authors.forename: Jon A
authors.initials: JA
authors.lastname: Hardie
mesh_terms: D000328:Adult; D000368:Aged; D002245:Carbon Dioxide / Q000097:blood; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D010100:Oxygen / Q000097:blood*; D011379:Prognosis; D016016:Proportional Hazards Models; D029424:Pulmonary Disease, Chronic Obstructive / Q000097:blood / Q000401:mortality*
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen
keywords: blood gas analysis; hypercapnia; hypoxemia; mortality; prognosis