Cardiac index is a hemodynamic parameter that relates the cardiac output (CO) from the 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 liters per minute per square meter (L/min/m2) . The cardiac index is calculated using the following formula:

CI = CO/BSA

where:

• CI: Cardiac index
• CO: Cardiac output
• BSA: Body surface area

The cardiac index 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 individuals body surface area. 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. If the cardiac index falls acutely below 2.2 L/min/m2, the patient may be in cardiogenic shock. The clinical significance of cardiac index comes from the fact that it is a measure of cardiac function that can be normalized for the patients body habitus, which means that the clinician can gain critical insight into the patients heart function given the variations in body type. Physicians use the cardiac index to make decisions on medications, treatment options, and educate patients on prognosis given these objective parameters.