Lack of equivalence between central and mixed venous oxygen saturation.
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.
Chawla
Lakhmir S
LS
The George Washington University MFA, 2150 Pennsylvania Ave NW, Suite 5-404, Washington, DC 20037, USA.
Zia
Hasan
H
Gutierrez
Guillermo
G
Katz
Nevin M
NM
Seneff
Michael G
MG
Shah
Muhammed
M
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
D006454:Hemoglobins; D010100:Oxygen