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),^[1] 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:

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

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 at 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 acutely below 2.2 L/min/m², the patient may be in cardiogenic shock.

References