What is the normal cardiac index (Cardiac output indexed to body surface area)?

• A. 1.5-2 L/min/m2
• B. 3-5 L/min/m2
• C. 2.5-4 L/min/m2
• D. 4-6 L/min/m2

Answer: (C)

Cardiac index is the amount of blood the heart pumps per minute after adjusting for body size, so it reflects heart performance relative to how big a person is. It’s calculated by dividing cardiac output by body surface area (CI = CO / BSA). The normal range you should memorize is about 2.5 to 4.0 L/min per square meter. This range fits typical CO values across different body sizes when scaled to surface area. For instance, a CO near 5 L/min with a body surface area around 1.7 m^2 gives a CI in the lower to middle part of that normal span, illustrating how indexing keeps interpretation consistent across individuals.

Understanding this helps interpret perfusion status: a CI below roughly 2.5 often signals inadequate perfusion for the body's needs, suggesting possible cardiogenic or distributive problems. A CI above around 4 can occur with high-output states such as sepsis or certain anemia forms, where the heart pumps a lot but tissues may still be under different kinds of stress. So, recognizing the normal CI range as 2.5–4.0 L/min/m^2 helps you assess whether the heart is meeting the body's size-adjusted demand for blood flow.