What is the normal difference between arterial and mixed venous oxygen content (C(a-v)O2)?

• A. 1-2%
• B. 4-5%
• C. 6-8%
• D. 10-15%

Answer: (B)

The distance between arterial and mixed venous oxygen content shows how much oxygen tissues extract from the blood. In a healthy adult, arterial O2 content is about 20 mL O2 per dL and mixed venous is around 15–16 mL per dL, giving a normal difference of roughly 4–5 mL O2 per dL, or about 4–5%. This reflects the amount of O2 delivered and used by tissues, and it’s tied to the Fick principle: VO2 = Cardiac output × (CaO2 − CvO2). If delivery drops or extraction increases, the difference widens; if delivery is high or extraction is low, the difference narrows. The other options are outside the typical resting range: 1–2% is too small, while 6–8% and 10–15% are larger than normal.