A high mixed venous oxygen saturation (SvO2) most likely indicates which of the following conditions?

• A. Low cardiac output with high tissue oxygen extraction
• B. Normal oxygen consumption with stable delivery
• C. High cardiac output with reduced tissue oxygen extraction or a shunt
• D. Decreased oxygen delivery due to anemia

Answer: (C)

SvO2 reflects the balance between oxygen delivery (DO2) and tissue oxygen consumption (VO2). A high SvO2 means delivery is greater than demand or that tissues are extracting less oxygen, or oxygenated blood is bypassing tissues via a shunt. When cardiac output is high, DO2 rises; if tissues aren’t extracting much oxygen (or there’s a shunt), the mixed venous blood retains more oxygen, raising SvO2. That’s why the scenario described—high cardiac output with reduced tissue oxygen extraction or a shunt—best fits a high SvO2. In contrast, low cardiac output with high extraction lowers SvO2; normal delivery with stable VO2 would not inherently be high; and decreased oxygen delivery from anemia typically lowers SvO2 due to increased extraction.