Cardiac Index Calculator

What is Cardiac Index?

Cardiac index (CI) is a vital clinical measurement used to determine how effectively a person’s heart is pumping blood. It adjusts cardiac output (CO) — the volume of blood the heart pumps per minute — based on the individual's body surface area (BSA). This allows for a more accurate evaluation of cardiac function, especially when comparing people of different sizes.

Medical professionals frequently use the cardiac index in intensive care and cardiac units to assess if the heart is supplying enough blood and oxygen to tissues across the body.

Cardiac Index Formula and Normal Range

To calculate the cardiac index, use this formula:

CI = CO / BSA

Where:

• CI = cardiac index (in liters per minute per square meter, L/min/m²)
• CO = cardiac output (in L/min)
• BSA = body surface area (in m²)

The normal cardiac index range is 2.5 to 4.0 L/min/m². A result below 2.0 L/min/m² may indicate cardiogenic shock, a life-threatening condition requiring immediate attention.

Besides using a formula, echocardiography with Doppler ultrasound can also measure cardiac output and index.

How to Calculate Cardiac Output and Body Surface Area

Cardiac Output (CO)

You can estimate cardiac output using:

CO = SV × HR

Where:

• SV = stroke volume (amount of blood ejected with each heartbeat, in mL)
• HR = heart rate (beats per minute)

Body Surface Area (BSA)

To estimate BSA, this calculator applies the Haycock formula:

BSA = 0.024265 × height^0.3964 × weight^0.5378

Where:

• Height is in centimeters (cm)
• Weight is in kilograms (kg)

This gives a personalized value in square meters (m²), taking both height and weight into account.

Example: How to Calculate Cardiac Index Step-by-Step

Let’s walk through a practical example using the cardiac index formula.

1. Calculate Cardiac Output (CO)
   CO = SV × HR
   CO = 70 × 64 = 4,480 mL = 4.48 L/min
2. Calculate BSA Using Haycock Formula
   BSA = 0.024265 × (169)^0.3964 × (71)^0.5378 ≈ 1.835 m²
3. Compute Cardiac Index (CI)
   CI = CO / BSA
   CI = 4.48 / 1.835 ≈ 2.44 L/min/m²

Conclusion: The patient’s cardiac index is 2.44 L/min/m², which is within the normal range, indicating adequate cardiac function.