From the Guidelines
The cardiac index is calculated by dividing the cardiac output by the body surface area, with the formula being CI = CO/BSA, where CI is cardiac index (measured in L/min/m²), CO is cardiac output (measured in L/min), and BSA is body surface area (measured in m²) 1. To determine the cardiac index, one must first measure the cardiac output, which can be achieved through methods such as thermodilution, Doppler echocardiography, or the Fick method.
- The cardiac output can be calculated using the volumetric method, which involves measuring the stroke volume and multiplying it by the heart rate.
- Alternatively, the Doppler method can be used, which measures the velocity time integral of the left ventricular outflow tract and multiplies it by the cross-sectional area of the outflow tract. Once the cardiac output is determined, the body surface area can be calculated using formulas such as the DuBois formula (BSA = 0.007184 × height(cm)^0.725 × weight(kg)^0.425) or the Mosteller formula (BSA = √(height(cm) × weight(kg)/3600)) 1. The cardiac index is a crucial parameter in assessing cardiac function, as it normalizes cardiac output for body size, allowing for a more accurate evaluation of cardiac performance across different individuals.
- Normal cardiac index values typically range from 2.5 to 4.0 L/min/m² in adults at rest, with values below this range potentially indicating cardiac dysfunction 1. It is essential to note that the cardiac index can be influenced by various factors, including age, sex, and body size, and therefore, should be interpreted in the context of individual patient characteristics 1.
From the Research
Cardiac Index Formula
The cardiac index (CI) is calculated by dividing the cardiac output (CO) by the body surface area (BSA) of an individual. The formula for cardiac index is:
- CI = CO / BSA Where:
- CI is the cardiac index in liters per minute per square meter (L/min/m²)
- CO is the cardiac output in liters per minute (L/min)
- BSA is the body surface area in square meters (m²)
Calculation of Cardiac Output
Cardiac output can be measured using various methods, including thermodilution 2, 3, 4, 5 and Doppler echocardiography 2, 5, 6. The choice of method may depend on the clinical setting and the availability of equipment.
Body Surface Area Calculation
Body surface area can be calculated using various formulas, such as the Mosteller formula or the Du Bois formula 4. The choice of formula may depend on the individual's body size and shape.
Reference Values for Cardiac Index
Reference values for cardiac index have been established in adults, with normal limits ranging from 1.9 to 4.3 L/min/m² 6. These values can be used to define low- and high-output states in clinical practice.