Cardiac index
Definition
The Cardiac Index (CI) is a hemodynamic parameter that measures the cardiac output (CO) of a person, adjusted to their body surface area (BSA). This makes it a more precise measure of the heart's efficiency than cardiac output alone, as it takes into account the individual's body size. The unit of measurement for cardiac index is liters per minute per square meter (L/min/m²).
Calculation
The formula for calculating the cardiac index is CI = CO/BSA. Cardiac output is measured in liters per minute (L/min), and body surface area is measured in square meters (m²).
Normal Values
In healthy adults, the normal range for cardiac index is typically between 2.5 and 4.0 L/min/m². However, these values can vary depending on the individual's age, sex, and overall health status.
Clinical Significance
The cardiac index is a crucial measure in critical care medicine and cardiology. It is often used to assess the severity of heart failure and to guide treatment decisions. A low cardiac index may indicate that the heart is not pumping enough blood to meet the body's needs, which can lead to symptoms such as fatigue, shortness of breath, and fluid retention. On the other hand, a high cardiac index may suggest that the heart is working too hard, which can increase the risk of heart damage and other complications.
Measurement
The cardiac index can be measured directly using invasive methods, such as a pulmonary artery catheter, or indirectly using non-invasive methods, such as echocardiography or Doppler ultrasound. Each method has its advantages and disadvantages, and the choice of method depends on the patient's condition and the resources available.
Limitations
While the cardiac index is a valuable tool in assessing cardiac function, it has its limitations. For example, it does not provide information on the distribution of blood flow within the body, which can be affected by factors such as blood pressure and vascular resistance. Furthermore, the cardiac index can be influenced by changes in body surface area, such as those that occur with weight gain or loss.