Which equation describes systemic oxygen delivery (DO2)?

Which equation describes systemic oxygen delivery (DO2)?

• A. DO2 = CO × CaO2
• B. DO2 = CO × CvO2
• C. DO2 = VO2 × CaO2
• D. DO2 = HR × CaO2

Answer: (A)

Systemic oxygen delivery depends on how much blood is pumped per minute and how much oxygen that blood can carry. That’s captured by DO2 = CO × CaO2. Cardiac output (CO) is the amount of blood the heart moves each minute, which comes from heart rate times stroke volume. CaO2 is the arterial oxygen content—the amount of oxygen carried by each liter of arterial blood—determined by hemoglobin amount, how saturated it is with oxygen, and a small amount dissolved in plasma. In practice CaO2 includes the large, oxygen-bound portion (1.34 × Hb × SaO2) plus a small dissolved part (0.003 × PaO2). This is why arterial oxygen content, not venous content, defines delivery: CaO2 reflects what is available for tissues as blood leaves the heart. The oxygen content in venous blood, CvO2, is used to describe how much oxygen remains after tissues extract some (in the equation VO2 = CO × (CaO2 − CvO2)), not how much can be delivered. So, the correct expression uses CO for flow and CaO2 for the delivered oxygen content to that flow, reflecting the supply side of oxygen to the body's tissues.

Systemic oxygen delivery depends on how much blood is pumped per minute and how much oxygen that blood can carry. That’s captured by DO2 = CO × CaO2. Cardiac output (CO) is the amount of blood the heart moves each minute, which comes from heart rate times stroke volume. CaO2 is the arterial oxygen content—the amount of oxygen carried by each liter of arterial blood—determined by hemoglobin amount, how saturated it is with oxygen, and a small amount dissolved in plasma. In practice CaO2 includes the large, oxygen-bound portion (1.34 × Hb × SaO2) plus a small dissolved part (0.003 × PaO2).

This is why arterial oxygen content, not venous content, defines delivery: CaO2 reflects what is available for tissues as blood leaves the heart. The oxygen content in venous blood, CvO2, is used to describe how much oxygen remains after tissues extract some (in the equation VO2 = CO × (CaO2 − CvO2)), not how much can be delivered.

So, the correct expression uses CO for flow and CaO2 for the delivered oxygen content to that flow, reflecting the supply side of oxygen to the body's tissues.