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