title: Lack of equivalence between central and mixed venous oxygen saturation.
abstract: OBJECTIVE
  We compared paired samples of central venous O(2) saturation (Scvo(2)) and mixed venous O(2) saturation (Svo(2)) to test the hypothesis that Scvo(2) is equivalent to Svo(2). We also compared O(2) consumption (Vo(2)) computed with Scvo(2) (Vo(2)cv) to that computed with Svo(2) (Vo(2)v).
  
  
  METHODS
  Prospective, sequential, observational study.
  
  
  METHODS
  Combined medical-surgical ICU.
  
  
  METHODS
  Fifty-three individuals > 18 years of age of either sex who required a pulmonary artery catheter (PAC) to guide fluid therapy. Subjects were identified as postsurgical (32 patients) or medical (21 patients) according to their ICU admission diagnosis.
  
  
  METHODS
  A PAC was inserted through the internal jugular or subclavian veins. Care was taken to place the PAC proximal port approximately 3 cm above the tricuspid valve. Blood samples were drawn from the proximal and distal ports in random order. An arterial blood sample also was drawn.
  
  
  METHODS
  Cardiac output in triplicate, systemic pressure, and central pressure. We analyzed blood samples for hemoglobin concentration and O(2) saturation (So(2)). Data were compared by correlation analysis and by the method of Bland and Altman.
  
  
  RESULTS
  Svo(2) was consistently lower than Scvo(2) (p < 0.0001), with a mean (+/-SD) bias of -5.2 +/- 5.1%. Similar differences in Scvo(2) and Svo(2) were present within each subgroup (p < 0.001). A lower Svo(2) resulted in Vo(2)v values that were higher than the Vo(2)cv values for all patients in the study (mean Vo(2)v, 236.7 +/- 103.4 mL/min; mean Vo(2)cv, 191.1 +/- 84.0 mL/min; p < 0.001) as well as for patients within each subgroup (p < 0.001).
  
  
  CONCLUSIONS
  Measurements of Scvo(2) and Svo(2) were not equivalent in this sample of critically ill patients. Moreover, substituting Scvo(2) for Svo(2) in the calculation of Vo(2) produced unacceptably large errors. The decrease in So(2) between Scvo(2) to Svo(2) may result from the mixing of atrial and coronary sinus blood. As such, this difference may be a marker of myocardial O(2) consumption.
authors.affiliation: The George Washington University MFA, 2150 Pennsylvania Ave NW, Suite 5-404, Washington, DC 20037, USA.
authors.forename: Lakhmir S
authors.initials: LS
authors.lastname: Chawla
authors.forename: Hasan
authors.initials: H
authors.lastname: Zia
authors.forename: Guillermo
authors.initials: G
authors.lastname: Gutierrez
authors.forename: Nevin M
authors.initials: NM
authors.lastname: Katz
authors.forename: Michael G
authors.initials: MG
authors.lastname: Seneff
authors.forename: Muhammed
authors.initials: M
authors.lastname: Shah
mesh_terms: D002407:Catheterization, Swan-Ganz; D016638:Critical Illness; D005260:Female; D006325:Heart Atria; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D010092:Oximetry / Q000379:methods; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption; D014680:Veins; D014684:Venae Cavae
chemical_list: D006454:Hemoglobins; D010100:Oxygen