Normal ScvO2 Values
Normal central venous oxygen saturation (ScvO2) is approximately 75%, with a generally accepted normal range of 70-75%. 1, 2
Physiological Context
- ScvO2 represents the balance between oxygen delivery and consumption, serving as an indirect indicator of whether cardiac output is adequate to meet tissue metabolic demands 2
- The normal value of approximately 75% reflects adequate oxygen delivery when arterial saturation is 100%, hemoglobin is adequate, and cardiac output meets metabolic needs 1
- Mixed venous oxygen saturation (SvO2) from the pulmonary artery is slightly lower, with normal values of approximately 70-75%, and the normal mixed venous PO2 is approximately 6 kPa (45 mmHg) 2
Clinical Thresholds for Intervention
- ScvO2 values below 70% indicate inadequate oxygen delivery relative to consumption and warrant intervention in critically ill patients 1, 2
- In septic shock resuscitation protocols, the target threshold is ScvO2 ≥70% (or SvO2 ≥65%) 1, 2
- For pediatric patients, the same threshold of >70% is recommended to ensure adequate oxygen delivery 1
Important Clinical Caveats
- A normal or high ScvO2 does not exclude tissue hypoxia, particularly in septic patients where impaired oxygen extraction is characteristic 1, 2
- In sepsis, ScvO2 may be normal or even supranormal (>70%) despite ongoing tissue hypoxia due to reduced oxygen extraction ratio 1
- Abnormally high ScvO2 values (>80-85%) in late septic shock are associated with increased mortality, likely reflecting impaired cellular oxygen utilization rather than adequate resuscitation 3
- Low oxygen extraction ratio (<0.2) combined with high ScvO2 (>70%) identifies a subset of septic patients with severe organ dysfunction and high mortality 4