A patient's oxygen consumption is measured at 250 mL/min. The arterial oxygen content is 20 mL/dL, and the mixed venous oxygen content is 15 mL/dL. Using the Fick principle, what is the cardiac output?

• A 2.5 L/min
• B 5.0 L/min ✓
• C 7.5 L/min
• D 10.0 L/min

Explanation

The Fick principle states cardiac output equals oxygen consumption divided by the arteriovenous oxygen difference. Here, 250 mL/min divided by 5 mL/dL equals 50 dL/min, which converts to 5.0 L/min. The 2.5 L/min distractor results from incorrectly dividing by the sum of the contents rather than the difference.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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