cardiac index
Summary
Cardiac index (CI) is cardiac output normalized for body surface area, calculated as CO/BSA with normal values 2.5-4.0 L/min/m². It provides a more accurate assessment of cardiac performance than cardiac output alone by accounting for patient size variations.
Detail
Cardiac index represents the cardiac output per unit of body surface area and is the most clinically useful measure of cardiac pump function. It is calculated by dividing cardiac output (stroke volume × heart rate) by body surface area (BSA), typically measured using the DuBois formula. Normal CI ranges from 2.5-4.0 L/min/m². Values below 2.2 L/min/m² indicate cardiogenic shock, while values 2.2-2.5 L/min/m² suggest cardiac compromise. CI is superior to cardiac output alone because it accounts for patient size - a larger person naturally requires higher cardiac output. It's measured invasively via pulmonary artery catheterization (Swan-Ganz) using thermodilution or Fick method, or non-invasively via echocardiography or bioimpedance. CI is crucial for managing critically ill patients, guiding inotropic therapy, and assessing cardiac function in heart failure, shock states, and perioperative care. Low CI may result from decreased contractility (MI, cardiomyopathy), reduced preload (hypovolemia), or increased afterload (hypertension).
Sources
- Harrison's Principles of Internal Medicine
- Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine
- Critical Care Medicine: Principles of Diagnosis and Management
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