Normal cardiac index in an adult is
**Core Concept**
The cardiac index is a vital sign that reflects the body's ability to deliver oxygen and nutrients to tissues. It is calculated as the cardiac output (CO) divided by the body surface area (BSA), providing a more accurate measure of cardiac function than cardiac output alone. The normal cardiac index is essential for assessing cardiac performance in various clinical scenarios.
**Why the Correct Answer is Right**
The normal cardiac index in an adult is approximately 2.5-4.2 liters per minute per square meter (L/min/m^2). This range is based on the average cardiac output of 5-6 liters per minute in a 70 kg adult, multiplied by the average body surface area of 1.7 square meters. The cardiac index takes into account the varying body surface areas of individuals, providing a standardized measure of cardiac function.
**Why Each Wrong Option is Incorrect**
* **Option A:** This value is lower than the normal range, indicating impaired cardiac function. A cardiac index below 2.5 L/min/m^2 may suggest cardiac dysfunction or severe hypovolemia.
* **Option B:** This value is within the upper limit of the normal range, but it is not the average value. A cardiac index above 4.2 L/min/m^2 may indicate increased cardiac workload or cardiac hypertrophy.
* **Option C:** This value is not a commonly accepted range for the cardiac index. It is essential to recognize the typical range of 2.5-4.2 L/min/m^2 to accurately diagnose and manage cardiac conditions.
**Clinical Pearl / High-Yield Fact**
A cardiac index below 2.5 L/min/m^2 is associated with increased morbidity and mortality in critically ill patients. Clinicians should be aware of this critical threshold to promptly identify and manage cardiac dysfunction.
**Correct Answer: C. 2.5-4.2 L/min/m^2**