Central venous and mixed venous oxygen saturation in critically ill patients

Background: Although mixed venous O-2 saturation (SvO(2)) accurately indicates the balance of O-2 supply/demand and provides an index of tissue oxygenation, the use of a pulmonary artery (PA) catheter is associated with significant costs, risks and complications. Central venous O-2 saturation (ScvO(2)), obtained in a less risky and costly manner, can be an attractive alternative to SvO(2). Objectives: To investigate whether the values of ScvO(2) and SvO(2) are well correlated and interchangeable in the evaluation of critically ill ICU patients and to create an equation that could estimate SvO(2) from ScvO(2). Methods: Sixty-one mechanically ventilated patients were catheterized upon admission and ScvO(2) and SvO(2) values were simultaneously measured in the lower part of the superior vena cava and PA respectively. Results: SvO(2) was 68.6 +/- 1.2% (mean +/- SEM) and ScvO(2) was 69.4 +/- 1.1%. The difference is statistically significant (p < 0.03). The correlation coefficient r is 0.945 for the total population, 0.937 and 0.950 in surgical and medical patients, respectively. In 90.2% of patients the difference was <5%. When regression analysis was performed, among 11 models tested, power model [SvO(2) = b0(ScvO(2))(b1)] best described the relationship between the two parameters (R-2 = 0.917). Conclusions: ScvO(2) and SvO(2) are closely related and are interchangeable for the initial evaluation of critically ill patients even if cardiac indices are different. SvO(2) can be estimated with great accuracy by ScvO(2) in 92% of the patients using a power model. Copyright (C) 2001 S. Karger AG, Basel.