In the described oxygen transfer system, the maximum oxygen transfer rate is measured as what percentage by volume?

• A. 3 vol %
• B. 5 vol %
• C. 6 vol %
• D. 8 vol %

Answer: (B)

Oxygen transfer rate in an oxygenator is described as the percentage of oxygen by volume that can be moved into the blood per pass. This maximum is constrained by how much oxygen the blood can carry—primarily the hemoglobin saturation limit—and by how readily oxygen diffuses across the membrane, which depends on the gas-side driving force and the membrane area.

Under typical oxygenator design and CPB conditions, the practical upper limit is about 5 vol% O2 per pass. That corresponds to roughly 5 mL of O2 transferred per 100 mL of blood (about 50 mL per liter). Beyond this, even higher gas tensions or flow won't significantly increase transfer because the blood columns reach near-full saturation and diffusion becomes the bottleneck.

So 5 vol% is the best answer because it reflects the common, physically limited maximum rate of O2 transfer across a membrane oxygenator under standard operating conditions.