Central Venous and Mixed Venous Oxygen Saturation in Critically Ill Patients

Abstract

Background: Although mixed venous O₂ saturation (SvO₂) accurately indicates the balance of O₂ 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 O₂ saturation (ScvO₂), obtained in a less risky and costly manner, can be an attractive alternative to SvO₂. Objectives: To investigate whether the values of ScvO₂ and SvO₂ are well correlated and interchangeable in the evaluation of critically ill ICU patients and to create an equation that could estimate SvO₂ from ScvO₂. Methods: Sixty-one mechanically ventilated patients were catheterized upon admission and ScvO₂ and SvO₂ values were simultaneously measured in the lower part of the superior vena cava and PA respectively. Results: SvO₂ was 68.6 ± 1.2% (mean ± SEM) and ScvO₂ 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 [SvO₂ = b0(ScvO₂)^b1] best described the relationship between the two parameters (R² = 0.917). Conclusions: ScvO₂ and SvO₂ are closely related and are interchangeable for the initial evaluation of critically ill patients even if cardiac indices are different. SvO₂ can be estimated with great accuracy by ScvO₂ in 92% of the patients using a power model.

Guiding Goal-Directed Therapy

“…Reinhart et al have shown that ScvO 2 has a good correlation with SvO 2 [86]. However, there is still debate regarding the equivalence between these two values [87][88][89][90] especially when they are low [91]. The surviving Sepsis Campaign recognized the clinical importance of ScvO 2 and recommended to keep ScvO 2 more than 70 % during the resuscitation of septic shock patients.…”

Agreement between Central and Mixed Venous Oxygen Saturation Following Cardiac Surgery

“…Consequently, ScvO 2 is usually less than SvO 2 mainly due to high oxygen content in renal venous drainage2, this relationship changes in sick patients with hemodynamic changes, oxygen extraction become higher in renal and splanchnic circulation resulting in reversal of SvO 2 -to-ScvO 2 relationship [19]. [20], this included critically ill ICU patients [21], and during liver transplantation [22]. On the other hand, other studies presented an unacceptable agreement between both measurements [4,5,23,24].…”

Venous oximetry

“…The relationship between the two variables may also be affected by various clinical situations and has been investigated in many experimental and clinical studies with different conclusions. Several studies demonstrated the reversed relationship of SvO 2 and ScvO 2 in shock (7,8). During cardiogenic and hypovolemic shock mesenteric and renal flow decreases followed by an increase in oxygen extraction.…”