The rate of oxygen transfer in the system is reported as what percentage by volume?

• A. 4 vol %
• B. 5 vol %
• C. 6 vol %
• D. 7 vol %

Answer: (B)

The rate of oxygen transfer in a perfusion system is the amount of oxygen the oxygenator adds to the blood, expressed as a volume percent (ml O2 per 100 ml blood). This reflects how much O2 content rises across the oxygenator for a given blood flow.

At rest, a typical adult consumes about 250 mL of O2 per minute. With common CPB flows around 4–5 L/min, the oxygenator usually increases the blood’s O2 content by roughly 50 mL O2 per liter of blood, which translates to about 5 mL O2 per 100 mL of blood, i.e., 5 vol%. This is why 5 vol% is considered the standard rate under normal resting conditions.

If metabolic demand or flow changes, the rate can shift toward higher values (e.g., 6–7 vol%), but 5 vol% best represents the usual operating point.