Cardiac index

Cardiac index (CI) is a haemodynamic parameter that relates the cardiac output (CO) from left ventricle in one minute to body surface area (BSA), thus relating heart performance to the size of the individual. The unit of measurement is litres per minute per square metre (L/min/m²).

Calculation

The index is usually calculated using the following formula:

$\text{CI} = \frac{\text{CO}}{\text{BSA}} = \frac{\text{SV}\times\text{HR}}{\text{BSA}}$

where

CI 

Cardiac index

BSA 

Body surface area

SV 

Stroke volume

HR 

Heart rate

CO 

Cardiac output

Clinical significance

The normal range of cardiac index in rest is 2.6–4.2 L/min/m².

The cardiac index is frequently measured and used in both intensive care medicine and cardiac intensive care. The CI is a useful marker of how well the heart is functioning as a pump by directly correlating the volume of blood pumped by the heart with an individual's body surface area.

If the CI falls below 2.2 L/min/m², the patient may be in cardiogenic shock.