From the Guidelines
The normal value of the cardiac index (CI) is greater than 2 liters per kilogram per minute (l/kg/min). This measurement is crucial for assessing cardiac function, particularly in patients with acute myocardial infarction, as it helps guide treatment decisions and monitor response to interventions 1. The cardiac index is calculated by dividing cardiac output by body weight, providing a more accurate assessment of heart function compared to cardiac output alone. In clinical practice, a cardiac index of greater than 2 l/kg/min is often aimed for, especially in critically ill patients, to ensure adequate perfusion of vital organs. Key factors that influence cardiac index include left ventricular function, filling pressures, and the use of inotropic agents such as dopamine and dobutamine, which may be administered to improve cardiac function and renal perfusion 1. Some important considerations when interpreting cardiac index values include:
- The impact of body size on cardiac index, with larger individuals requiring higher cardiac outputs to maintain adequate perfusion
- The effects of various medications, such as inotropes and vasopressors, on cardiac index and overall hemodynamics
- The relationship between cardiac index and other hemodynamic parameters, such as pulmonary wedge pressure and systemic vascular resistance. In the context of acute myocardial infarction, maintaining a cardiac index greater than 2 l/kg/min is essential for optimizing patient outcomes, including reducing morbidity and mortality, and improving quality of life 1.
From the Research
Normal Value of Cardiac Index (CI)
The normal value of the cardiac index (CI) can vary depending on the population being studied.
- In healthy older individuals, the mean cardiac index is reported to be between 2.1 and 3.2 L/min/m2 2.
- In critically ill children, the mean cardiac index is reported to be 3.5 +/- 1.3 L/min per m2 3.
- In patients with cardiovascular disease, the mean cardiac index is reported to be 2.9 (0.8) l/min/m 4.
Factors Affecting Cardiac Index
Several factors can affect the cardiac index, including:
- Age: the cardiac index may decline with age, with a reported yearly decline of between 3.5 and 8 mL/min/m2 per year 2.
- Cardiac function: patients with impaired cardiac function may have a lower cardiac index 5, 4.
- Exercise: the cardiac index can increase with exercise, and the incremental increase in cardiac index (delta CI) can be used to evaluate exercise capacity in patients with congestive heart failure 5.
Measurement of Cardiac Index
The cardiac index can be measured using various techniques, including:
- Femoral arterial thermodilution: this technique is suitable for measuring cardiac output in critically ill children 3.
- Pulmonary thermodilution: this technique is more invasive than femoral arterial thermodilution, but can provide accurate measurements of cardiac output 3.
- Benchmark Exercise Test device: this device can be used to calculate cardiac index using oxygen uptake, carbon dioxide output, and respired flow 5.