Feature

Mixed Venous Oxygen Saturation (SvO₂)

Central Venous Oxygen Saturation (ScvO₂)

Definition

Percentage of hemoglobin saturated with oxygen in true mixed venous blood returning to the lungs

Percentage of hemoglobin saturated with oxygen in blood from the upper body venous return

Sampling Site

Pulmonary artery

Superior vena cava / Right atrium

Catheter Required

Pulmonary Artery Catheter (PAC / Swan–Ganz)

Central Venous Catheter (CVC)

Blood Source Composition

Mixture of venous blood from: 

• SVC 

• IVC 

• Coronary sinus

Primarily venous blood from: 

• Brain 

• Upper limbs

Physiological Accuracy

Gold standard for global oxygen balance

Surrogate marker of global oxygen balance

Normal Value

65–75%

70–80%

Typical Relationship

Higher than ScvO₂(in normal physiology)

Higher  than SvO₂ when critically ill 

Reflects Global VO₂?

YES (accurately)

PARTIALLY

Represents Lower Body Oxygen Extraction?

YES

NO

Affected by Regional Blood Flow Redistribution

Less affected

More affected

Continuous Monitoring

Possible (fiberoptic PAC)

Possible (specialized CVC)

Ease of Measurement

Invasive, technically demanding

Easier, widely available

Complication Risk

Higher (PA rupture, arrhythmia, infection)

Lower

Cost & Resource Requirement

High

Lower

Use in Routine ICU Practice

Declining

Common

Use in Early Goal-Directed Therapy (EGDT)

Rare

Primary target (≥70%)

Guideline Preference (Sepsis)

Not routinely recommended

Preferred surrogate

Sensitivity to Myocardial Ischemia

YES

NO

Reliability in Cardiogenic Shock

High

Lower

Reliability in Septic Shock

High

Variable

Reliability in Post-Cardiac Surgery

Superior

Less reliable

Effect of Increased Cerebral O₂ Extraction

Minimal impact

Marked decrease

Effect of High Splanchnic O₂ Extraction

Detected

Missed

Effect of Hyperdynamic Sepsis

May remain low despite high CO

Often falsely normal or high

Use in Advanced Hemodynamic Assessment

Preferred

Limited

Trend Monitoring Utility

Excellent

Good (with context)

Exam Answer Status

Gold standard

Practical bedside surrogate