ScvO2

ScvO2 stands for central venous oxygen saturation. It is the percentage of hemoglobin carrying oxygen in blood returning to the heart through the superior vena cava. In clinical practice, ScvO2 is measured from blood samples drawn via a central venous catheter and analyzed with co-oximetry; continuous noninvasive monitoring is possible with specialized catheter systems that integrate optical sensors.

Physiologically, ScvO2 reflects the balance between systemic oxygen delivery (DO2) and consumption (VO2). It is influenced by arterial oxygen content (derived from SaO2 and hemoglobin), cardiac output, and tissue oxygen extraction. A low ScvO2 typically indicates insufficient oxygen delivery or increased extraction, while a high ScvO2 can indicate reduced oxygen use or a delivery–consumption mismatch. In septic or inflammatory states, elevated ScvO2 may occur despite poor perfusion due to impaired cellular oxygen utilization or other factors.

Normal values for ScvO2 are typically around 70% in healthy individuals, with a commonly cited reference range of roughly 65–75%. ScvO2 is often compared to SvO2 (mixed venous oxygen saturation) obtained from the pulmonary artery; ScvO2 is usually a few percentage points higher than SvO2 because of the venous drainage pattern from the upper body, though the exact difference can vary.

Clinical use and interpretation: ScvO2 has been used to guide resuscitation in critical illness, notably in early goal-directed therapy for septic shock, where targets around 70% were proposed. More recent guidelines emphasize a holistic assessment, using ScvO2 alongside lactate, perfusion parameters, and hemodynamics. Limitations include its imperfect reflection of tissue oxygenation, potential sampling artifacts, and differences from SvO2 in various pathophysiologies.