Central venous and mixed venous oxygen saturation in critically ill patients

Background: Although mixed venous O-2 saturation (SvO(2)) accurately indica tes the balance of O-2 supply/demand and provides an index of tissue oxygen ation, the use of a pulmonary artery (PA) catheter is associated with signi ficant costs, risks and complications. Central venous O-2 saturation (ScvO( 2)), obtained in a less risky and costly manner, can be an attractive alter native to SvO(2). Objectives: To investigate whether the values of ScvO(2) and SvO(2) are well correlated and interchangeable in the evaluation of cri tically ill ICU patients and to create an equation that could estimate SvO( 2) from ScvO(2). Methods: Sixty-one mechanically ventilated patients were c atheterized upon admission and ScvO(2) and SvO(2) values were simultaneousl y 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 correlati on coefficient r is 0.945 for the total population, 0.937 and 0.950 in surg ical and medical patients, respectively. In 90.2% of patients the differenc e was <5%. When regression analysis was performed, among 11 models tested, power model [SvO(2) = b0(ScvO(2))(b1)] best described the relationship betw een the two parameters (R-2 = 0.917). Conclusions: ScvO(2) and SvO(2) are c losely related and are interchangeable for the initial evaluation of critic ally ill patients even if cardiac indices are different. SvO(2) can be esti mated with great accuracy by ScvO(2) in 92% of the patients using a power m odel. Copyright (C) 2001 S. Karger AG, Basel.