What is a Cardiac Index?

Erin J. Hill

A cardiac index is a system used to measure cardiac output, or the amount of blood pumped out of the left ventricle each minute. This system is useful in helping to diagnose and treat a wide range of heart problems when used in combination with other tools. To figure out the cardiac index of a patient, a doctor takes the amount of blood pumped per minute in liters and divides it by the patient's body surface area (BSA).

More or less cardiac output than necessary is known as high or low blood pressure.
More or less cardiac output than necessary is known as high or low blood pressure.

One reason for using this index to measure heart function is to better understand the effects of certain medical procedures on the heart. Measurements may be taken throughout a procedure to note any changes on the cardiac index and other factors to get a clear picture of how stressful a surgery or procedure is on the heart. This is especially useful during heart surgeries, primarily bypass surgeries.

Obesity may affect a person's cardiac output.
Obesity may affect a person's cardiac output.

To get an accurate reading, the cardiac index score is generally taken before a procedure is begun and then throughout or after the procedure at certain intervals. A normal heart with adequate cardiac activity pumps about 5 or 6 liters (5.28 or 6.34 quarts) of blood through the body every minute while the person is at rest. Any more or less than this can cause serious problems in the body. More or less cardiac output than necessary is also know as high or low blood pressure.

The cardiac index allows doctors to get a clear picture of how stressful surgery is on the heart.
The cardiac index allows doctors to get a clear picture of how stressful surgery is on the heart.

Professionals may also study the effects of certain medical conditions or stressors on a person's cardiac index reading. Obesity, for example, is an important topic of study because the recent epidemic in many of the world's industrialized nations is taking a toll on the health of the general population. Unfortunately, because the problem of widespread obesity is fairly recent in development, the long-term effects of extreme weight gain have not been fully studied. Using this index on those with large BSA readings is a good way of measuring the effects of extra weight on the heart, and to determine how much excess weight is required to create serious problems.

A cardiac index is a system used to measure the amount of blood pumped out of the left ventricle each minute.
A cardiac index is a system used to measure the amount of blood pumped out of the left ventricle each minute.

The cardiac index, combined with other diagnostic equipment, is an effective way to determine overall heart health. Doctors also gain a better perspective at the effects on surgery and other procedures on certain types of patients. These include the morbidly obese, those with certain existing heart conditions, and those with other serious ailments.

Obesity is a public health problem in many industrialized nations.
Obesity is a public health problem in many industrialized nations.

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