Cardiac Index Calculator – Heart Function Assessment
Calculate cardiac index to assess heart function relative to body size
How to Use
- Enter the cardiac output in liters per minute (L/min)
- Enter your weight and height
- Select your preferred units
- Click calculate to see your cardiac index
What is Cardiac Index?
Cardiac index (CI) is a hemodynamic parameter that relates the cardiac output (CO) from the left ventricle in one minute to the body surface area (BSA), thus relating heart performance to body size.
The formula is: CI = CO / BSA, where CO is measured in liters per minute and BSA is measured in square meters. Normal cardiac index ranges from 2.5 to 4.0 L/min/m².
Clinical Significance
Cardiac index is more accurate than cardiac output alone because it accounts for differences in body size. A large person naturally has a higher cardiac output than a smaller person, but their cardiac indices may be similar.
| Cardiac Index | Classification | Clinical Implications |
|---|---|---|
| < 2.2 L/min/m² | Cardiogenic shock | Severe cardiac dysfunction, requires immediate intervention |
| 2.2 - 2.5 L/min/m² | Low cardiac index | May indicate heart failure or decreased cardiac function |
| 2.5 - 4.0 L/min/m² | Normal | Adequate cardiac function |
| > 4.0 L/min/m² | High cardiac index | May indicate hyperdynamic state, sepsis, or hyperthyroidism |
Body Surface Area (BSA)
Body surface area is calculated using the Mosteller formula: BSA (m²) = √[(height in cm × weight in kg) / 3600]. This is one of the most commonly used and accurate formulas for BSA calculation in clinical practice.
BSA is used in many medical calculations including drug dosing, medical indicators, and assessment of metabolic mass. Average BSA for adults is approximately 1.7 m².
Factors Affecting Cardiac Index
- Heart rate and rhythm
- Myocardial contractility (strength of heart muscle contraction)
- Preload (venous return to the heart)
- Afterload (resistance against which the heart pumps)
- Valve function
- Medications (inotropes, vasodilators, beta-blockers)
- Fluid status and blood volume
- Metabolic demands of the body
Frequently Asked Questions
- What is a normal cardiac index?
- A normal cardiac index is 2.5-4.0 L/min/m². Values below 2.5 may indicate cardiac dysfunction, while values above 4.0 may suggest a hyperdynamic state.
- How is cardiac index different from cardiac output?
- Cardiac output is the volume of blood pumped by the heart per minute, while cardiac index is cardiac output adjusted for body size (divided by body surface area). This makes cardiac index more useful for comparing cardiac function between people of different sizes.
- What does a low cardiac index mean?
- A low cardiac index (< 2.5 L/min/m²) may indicate heart failure, cardiogenic shock, or other conditions causing decreased cardiac function. Values below 2.2 L/min/m² are particularly concerning and may require immediate medical intervention.
- Can cardiac index be too high?
- Yes, a high cardiac index (> 4.0 L/min/m²) may indicate a hyperdynamic state, which can occur in conditions like sepsis, hyperthyroidism, severe anemia, or arteriovenous fistulas. While the heart is pumping more blood, this doesn't always mean better health.