How should venous saturations, such as central venous oxygen saturation (ScvO2) and mixed venous oxygen saturation (SvO2), be used to guide fluid management in critically ill patients?

From the Guidelines

Venous oxygen saturations, such as central venous oxygen saturation (ScvO2) and mixed venous oxygen saturation (SvO2), should be used as complementary tools to guide fluid management in critically ill patients, with target ScvO2 values of >70% or SvO2 >65% indicating adequate oxygen delivery relative to consumption.

Key Considerations

• When ScvO2 or SvO2 values are low, clinicians should first assess for hypovolemia and consider fluid administration if other signs of fluid responsiveness are present 1.
• However, fluid administration should be limited if venous saturations are already normal or high, as this suggests adequate oxygen delivery or potential utilization problems.
• These measurements should be interpreted alongside other hemodynamic parameters (blood pressure, heart rate, lactate levels), clinical assessment, and dynamic measures of fluid responsiveness.

Physiological Basis

• The physiological basis for using venous saturations is that they reflect the balance between oxygen delivery and consumption—low values suggest tissues are extracting more oxygen due to either inadequate delivery (potentially responsive to fluids) or increased consumption.
• Normal or high values with other signs of shock may indicate distributive problems or cellular utilization issues rather than volume deficits.

Clinical Application

• Continuous or serial measurements provide more valuable information than isolated readings when guiding resuscitation efforts.
• The use of CVP alone to guide fluid resuscitation can no longer be justified, and dynamic measures of assessing whether a patient requires additional fluid have been proposed to improve fluid management 1.
• A recent multicenter study demonstrated limited use of cardiac function monitors during fluid administration in the ICUs, highlighting the need for a detailed initial assessment and ongoing reevaluation of the response to treatment 1.

Guideline Recommendations

• The Surviving Sepsis Campaign guidelines recommend initial fluid resuscitation with at least 30 mL/kg of IV crystalloid fluid within the first 3 hours, with further fluids guided by frequent reassessment of hemodynamic status 1.
• The guidelines also suggest guiding resuscitation to normalize lactate in patients with elevated lactate levels as a marker of tissue hypoperfusion, although the quality of evidence is low 1.

From the Research

Venous Saturations in Fluid Management

• Venous saturations, such as central venous oxygen saturation (ScvO2) and mixed venous oxygen saturation (SvO2), can be used to guide fluid management in critically ill patients 2.
• However, the use of central venous pressure (CVP) to guide fluid administration has been challenged, and its reliability as a parameter of volume status or fluid responsiveness has been questioned 3.

Fluid Management Strategies

• The "salvage, optimization, stabilization, de-escalation" (SOSD) mnemonic can be used as a general guide to fluid resuscitation, with fluid administration adapted according to the course of the disease 4.
• A fluid challenge technique can be used to assess ongoing fluid requirements, and the type of fluid used can impact patient outcomes, with crystalloids and colloids having different effects on intravascular volume expansion and potential adverse effects 5, 6.
• The use of smaller volumes to perform fluid challenges, monitoring of extravascular lung water, and earlier use of norepinephrine can help reduce morbidity and mortality from severe sepsis 2.

Monitoring and Assessment

• Dynamic tests of fluid responsiveness, such as pulse pressure or stroke volume variation, can be used to assess fluid responsiveness, but are limited to a small percentage of critically ill patients 4.
• Sophisticated monitoring tools, such as echocardiography and transpulmonary thermodilution, can provide valuable data to guide fluid management 2.
• The measurement of ScvO2 and SvO2 can provide information on the adequacy of oxygen delivery and consumption, but its use as a sole guide for fluid management is not recommended 2.