The arterial-venous O2 content difference is typically reported in which units?

• A. mmHg
• B. mL/dL
• C. percent by volume
• D. L/min

Answer: (C)

The main concept here is that arterial-venous O2 content difference is a measure of how much oxygen is delivered to and extracted by tissues per volume of blood, expressed as a volume of O2 per volume of blood. This is a content quantity, so the units are milliliters of oxygen per deciliter of blood (mL O2/dL).

O2 content (CaO2 and CvO2) combines both oxygen bound to hemoglobin and dissolved oxygen in plasma, and is calculated in mL O2 per dL of blood. The arterial-venous difference is CaO2 minus CvO2, and its typical value is about 4–5 mL O2 per dL of blood at rest. This remains a content (volume per volume) measure, not a pressure or a rate.

The other options don’t fit the concept: mmHg is a pressure unit, which relates to oxygen partial pressure (not content); L/min is a flow rate; percent by volume would describe saturation (SaO2 or SvO2), not the actual amount of oxygen content per unit of blood.