What is the normal value of the cardiac index?

Appeared in: DSSSB 12 August 2024

Explanation

The Cardiac Index (CI) is a hemodynamic parameter that relates the cardiac output (CO) from the left ventricle in one minute to the body surface area (BSA), thus relating heart performance to the size of the individual.
The formula to calculate it is CI = CO / BSA.
The normal range for the cardiac index in a healthy resting adult is 2.5 to 4.0 L/min/m².
The value of 2.8 L/min/m² falls within this established normal range, making it the correct answer.

Option B: This value (3500 ml/minute or 3.5 L/min) represents a cardiac output, not a cardiac index, as it is not adjusted for body surface area (which would be in units of m²).
Option C: The value and unit (ml/minute) are incorrect. A normal stroke volume is approximately 70 ml per beat, not per minute.
Option D: This is the classic textbook value for an average resting cardiac output in an adult, not the cardiac index.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Normal value of Cardiac Index as background academic context rather than a clinical decision trigger.
Cardiac index is a more precise measure of heart function and tissue perfusion than cardiac output because it is standardized to the patient's size. It is crucial for managing critically ill patients.
A low CI (less than 2.2 L/min/m²) can be a sign of cardiogenic shock, severe heart failure, or hypovolemia, prompting immediate nursing interventions such as administering fluids, inotropes, or vasopressors as ordered.
Monitoring trends in CI is more important than a single value. A nurse observing a downward trend must assess for signs of decreased perfusion (e.g., altered mental status, decreased urine output, cool extremities) and report to the provider.

How to Approach the Question

First, identify the specific term in the question: 'cardiac index'.
Recall the definition of cardiac index: it is cardiac output adjusted for body surface area (BSA).
Pay close attention to the units of measurement. The unit for cardiac index must include a measure of volume, time, and area, which is typically L/min/m².
Examine the options. Only '2.8 L/min/m²' has the correct units for a cardiac index.
Confirm the value by recalling the normal physiological range for cardiac index, which is approximately 2.5 to 4.0 L/min/m². The value 2.8 is within this range.
Eliminate the other options by identifying what they represent: '5 L/minute' is a typical cardiac output, and '70 ml' is closer to a stroke volume per beat.

Concept Tested & Keywords

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E6 Physiology Ganong 27e Vol 2 Part 1 p. 91-93

E6 Nursing Fundamentals Potter Perry 12e Part 4 p. 231-233

Practise the full DSSSB 12 August 2024

Attempt every question from this paper in a timed mock, then review the full solution for each one.