From the Guidelines
Mixed venous oxygen saturation (SvO2) is a reliable indicator of tissue perfusion status, with a goal of above 66% in patients on extracorporeal membrane oxygenation (ECMO) 1.
Importance of SvO2 Monitoring
SvO2 measures the amount of oxygen remaining in the venous blood after tissues have extracted what they need, typically ranging from 60-80% in healthy individuals. A decrease in SvO2 indicates increased oxygen extraction by tissues, which often occurs when perfusion is inadequate relative to metabolic demands.
Clinical Application
This measurement is obtained from the pulmonary artery using a pulmonary artery catheter and serves as a global indicator of the balance between oxygen delivery and consumption. Low SvO2 values (below 60%) suggest inadequate cardiac output, decreased hemoglobin concentration, decreased arterial oxygen saturation, or increased oxygen consumption.
Management Strategies
In critical care settings, SvO2 monitoring helps guide interventions to improve tissue perfusion, such as:
- Fluid resuscitation
- Inotropic support
- Blood transfusions
- Adjustments to mechanical ventilation Continuous monitoring of SvO2 provides valuable information about a patient's hemodynamic status and response to therapeutic interventions 1.
Considerations in ECMO Patients
In peripherally cannulated patients on ECMO, it is essential to recognize the potential for differential upper and lower torso oxygenation, known as Harlequins or North-South syndrome, which can affect SvO2 measurements 1. Management of Harlequins includes increasing ECMO flow, manipulating ventilator settings, or inserting an additional cannula 1.
From the Research
Mixed Venous Oxygen Saturation Monitoring
- Mixed venous oxygen saturation (SvO2) is a useful indicator of cardiac output and overall tissue perfusion 2
- SvO2 monitoring provides valuable information about oxygen consumption and venous reserve, which are important measures in critically ill patients 3
- A fall in SvO2 can be related to abnormal hemodynamic status, abnormal oxygen demand, or abnormal oxygen supply 2
Comparison with Other Monitoring Parameters
- SvO2 has been compared to thermodilution cardiac output (COtd) in monitoring patients with severe heart failure, and SvO2 was found to be a more useful parameter in evaluating hemodynamic status and monitoring therapy 4
- Central venous saturation (ScvO2) has been suggested as an alternative to SvO2, but studies have shown that ScvO2 is less accurate than SvO2 and should not be used as a sole guiding variable for decision-making 3
Clinical Applications
- SvO2 monitoring can be used to assess the effectiveness of treatment in patients with advanced congestive heart failure 5
- SvO2 can be useful as a guide for both prognosis and urgency of therapy in critically ill patients 6
- A normal or high SvO2 value does not exclude disturbances such as anemia, arterial oxygen desaturation, or decreased cardiac output 6