In hemodynamic monitoring, which measurement best reflects global oxygen delivery relative to demand?

• A. Mixed venous oxygen saturation (SvO2)
• B. Central venous pressure (CVP)
• C. Cardiac output
• D. Arterial oxygen saturation

Answer: (A)

The crucial idea is the balance between oxygen delivery to tissues and oxygen demand (usage). Mixed venous oxygen saturation measures the amount of oxygen left in venous blood after the tissues have extracted what they need. It acts as a global readout of that delivery–consumption balance for the whole body.

If delivery is sufficient and tissues aren’t demanding more than they can handle, SvO2 stays near normal values. If delivery drops or tissue demand increases, tissues extract more oxygen, leaving less in the venous blood, so SvO2 falls. Conversely, an SvO2 that remains normal or rises can indicate adequate or reduced extraction rather than increased demand.

Other parameters don’t capture this global balance as directly: central venous pressure reflects preload; cardiac output contributes to delivery but alone doesn’t tell you how much oxygen is being used; arterial oxygen saturation indicates oxygen entering the system but not how much is being extracted by tissues.