Cardiac Index (CI)is used to calculate how much blood is pumped by the heart. The CI parameter relates the cardiac output (CO) to body surface area (BSA), thus relating heart performance to the size of an individual. The unit of measurement is litres per minute per square metre (L/min/m2).
Where:
CI = Cardiac Index
`Q_c` = Cardiac Output
SV = Stroke Volume
HR = Heart Rate
BSA = Body Surface Area in square metres.
The normal range of cardiac index in rest is 2.6 - 4.2 L/min/m2.
It is frequently measured and used in intensive care medicine, and cardiac intensive care. It 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 a patient's Cardiac Index (CI) falls below 1.8 L/min/m2, it will likely lead to a cardiogenic shock.