Do you know the cardiac output?
Yes
Cardiac output
L/min
Height
ft
Weight
lb
Results
Cardiac index
L/min/m²
The normal values for Cardiax Index range from 2.5 to 4 L/min/m² .

The cardiac index calculator estimates cardiac function based on the cardiac output from the left ventricle in one minute, and the body surface area of the patient. We frequently measure the patient's cardiac index (CI) and use it in intensive care medicine and cardiac intensive care. Read the article below to find out what is cardiac index, how to calculate it, and what the cardiac index formula looks like.

Here are other cardiovascular system calculators you might be interested in:

  • QTc calculator - perform a correction of QT interval for your patient’s heart rate;
  • CVD risk calculator - calculate 10-year risk for cardiovascular disease;
  • CHA2DS2 vasc calculator - assess the risk of stroke in patients with atrial fibrillation;
  • TIMI score - determine the 14 day risk of death or major health complications in patients with UA or NSTEMI; and
  • Duke treadmill score - predict the risk of ischemia or infraction in the heart for your patient.

We try our best to make our Omni Calculators as precise and reliable as possible. However, this tool can never replace professional medical advice.

What is cardiac index?

Cardiac index (CI) is an important parameter that assesses if the patient's heart is pumping enough blood and therefore delivering enough oxygen to the cells. It relates the cardiac output (CO) from left ventricle in one minute to body surface area (BSA), and therefore it takes into account the body size of the patient.

So, in general, we can say that the CI's function is to create a normalized value for the cardiac function, which effectively corrects for the patient's body size.

Cardiac index formula and normal cardiac index range

So you know the answer to the question: "What is cardiac index?", but what does the cardiac index formula look like? We present the equation below:

CI = CO / BSA

where:

CI - cardiac index, expressed in L/min/m²;

CO - cardiac output, expressed in L/min; and

BSA - body surface area, expressed in m².

The normal cardiac index range is between 2.5 L/min/m² to 4.0 L/min/m². A value under 2.0 L/min/m² is highly indicative of cardiogenic shock.

How to calculate cardiac output and body surface area?

You may be familiar with the values of the parameters mentioned in the previous paragraph, but what if you don't know them? Let's find out how to calculate cardiac output.

In the simplest terms, cardiac output is the volume of blood the heart pumps per minute. The CO formula is as follows:

CO = SV * HR

where:

CO - cardiac output, expressed in L/min;

SV - stroke volume (the blood volume ejected by one heartbeat), expressed in mL; and

HR - heart rate, expressed in beats per minute.

So now you know how to calculate cardiac output, but what about BSA? Our cardiac index calculator uses the Haycock formula, which is:

BSA = 0.024265 * height0.3964 * weight0.5378

where:

  • BSA is expressed in m²;
  • height is expressed in cm; and
  • weight is expressed in kg.

How to calculate cardiac index? - a practical example

You just found out how to calculate cardiac index, but let's use a practical example to make sure that everything is clear. Here are some details of our exemplary patient:

  • Cardiac output: unknown;
  • Stroke volume: 70 mL;
  • Heart rate: 64 beats per minute;
  • Weight: 71 kg; and
  • Height: 169 cm.

Don't worry about the units! Out calculator has a built-in unit converter.

  1. We will start the calculation by estimating the cardiac output of our patient:

CO = SV * HR

CO = 70 * 64

CO = 4480 mL = 4.48 L

  1. Now, we will calculate BSA:

BSA = 0.024265 * height0.3964 * weight0.5378

BSA = 0.024265 * 1690.3964 * 700.5378

BSA = 0.024265 * 7.64 * 9.82

BSA = 1.835 m²

  1. Finally, we can calculate the patient's cardiac index using the cardiac index formula:

CI = CO / BSA

CI = 4.48 / 1.835

CI = 2.44 L/min/m²

Our patient's result is equal to 2.46 L/min/m², so it is within the normal cardiac index range.

Joanna Michałowska, PhD candidate