A 45-year-old woman weighing 70 kg with a body surface area of 1.7 m² has a cardiac output of 5.1 L/min. What is her cardiac index?

• A 5.1 L/min/m²
• B 8.7 L/min/m²
• C 4.0 L/min/m²
• D 3.0 L/min/m² ✓

Explanation

Cardiac index is cardiac output divided by body surface area, allowing comparison between individuals of different sizes. Dividing 5.1 L/min by 1.7 m² gives 3.0 L/min/m², which lies within the normal range of about 2.5 to 4.0 L/min/m². Option A confuses cardiac output with cardiac index, and option B multiplies instead of dividing. Cardiac index is the preferred variable when assessing adequacy of output in hemodynamic monitoring.

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

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