Cardiac Index Calculator

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) (check the cardiac output calculator) from left ventricle in one minute to body surface area (BSA) (estimate it with BSA calculator), 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.

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.

Is there any other way to calculate the cardiac index and cardiac output?

The answer is yes. We may use echocardiography and perform measurements using the Doppler effect.

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, for more explanation take a look at the stroke volume calculator), expressed in mL; and

HR - heart rate, expressed in beats per minute, easily calculated with the heart rate calculator.

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∗weight0.5378BSA=0.024265∗height0.3964∗weight0.5378

where:

• BSA is expressed in m²;
• Height is expressed in cm; and
• Weight is expressed in kg.

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

2. Now, we will calculate BSA:

BSA=0.024265∗height0.3964∗weight0.5378BSA=0.024265∗height0.3964∗weight0.5378

BSA=0.024265∗1690.3964∗700.5378BSA=0.024265∗1690.3964∗700.5378

BSA = 0.024265 * 7.64 * 9.82

BSA = 1.835 m²

3. 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.