title: The accuracy of the central venous blood gas for acid-base monitoring.
abstract: BACKGROUND
  Routine use of central venous blood gases (VBGs) may reduce complications from prolonged arterial cannulation. We investigated the reliability of the VBG as a substitute for arterial blood gas (ABG) in multiple care settings.
  
  
  METHODS
  We developed a VBG adjustment rule of ABG pH = VBG pH + 0.05, ABG CO(2) = VBG PCO(2) -5 mm Hg from prior studies and validated this relationship with simultaneous venous and arterial blood obtained from 187 medical/surgical intensive care, cardiac catheterization laboratory, and coronary care unit patients with central venous access.
  
  
  RESULTS
  The overall accuracy of a normal adjusted VBG (aVBG) to predict a normal ABG was 90%. After adjustment, the mean systematic difference (bias) between ABG and VBG pH decreased from 0.035 +/- 0.02 to -0.015 +/- 0.02 and PCO(2) bias decreased from -4.5 +/- 3.5 to 0.5 +/- 3.5. Intraclass correlation coefficients for agreement improved after applying the adjustment rule to venous pH (from 0.84 to 0.93, P < .001) and PCO(2) (from 0.66 to 0.84, P < .001). Overall diagnostic accuracy of VBG improved from 45% to 74% after adjustment. Multiple logistic regression demonstrated that the factor independently associated with discrepancy between VBG and ABG diagnoses was an abnormal aVBG (OR 6.8, 95% CI 2.8-16.5).
  
  
  CONCLUSIONS
  Because of the high agreement between a normal aVBG with a normal ABG and the small bias between these tests, we recommend use of the adjusted central VBG.
authors.affiliation: Boston University Pulmonary Center, Boston, MA 02118, USA. allan.walkey@bmc.org
authors.forename: Allan J
authors.initials: AJ
authors.lastname: Walkey
authors.forename: Harrison W
authors.initials: HW
authors.lastname: Farber
authors.forename: Charles
authors.initials: C
authors.lastname: O'Donnell
authors.forename: Howard
authors.initials: H
authors.lastname: Cabral
authors.forename: Janet S
authors.initials: JS
authors.lastname: Eagan
authors.forename: George J
authors.initials: GJ
authors.lastname: Philippides
mesh_terms: D000136:Acid-Base Equilibrium / Q000502:physiology*; D001784:Blood Gas Analysis / Q000379:methods*; D002405:Catheterization, Central Venous; D006801:Humans; D007362:Intensive Care Units; D016015:Logistic Models; D010100:Oxygen / Q000097:blood*; D011446:Prospective Studies
chemical_list: D010100:Oxygen