Calculate cardiac output using the Fick principle or thermodilution. Includes cardiac index, stroke volume, and systemic vascular resistance.
Cardiac output (CO) — the volume of blood pumped by the heart each minute — is a fundamental hemodynamic parameter that reflects how well the heart is meeting metabolic demand. Normal resting CO in adults ranges from 4 to 8 L/min, but it can rise substantially during vigorous exercise or fall in heart failure and shock states.
The **Fick principle**, first described by Adolf Fick in 1870, remains one of the most physiologically grounded methods for determining CO. It is based on the concept that oxygen consumed by the body must equal the oxygen delivered by the heart minus the oxygen returned to it. The calculation uses oxygen consumption (VO₂), hemoglobin concentration, and the difference between arterial and mixed venous oxygen saturations.
The **thermodilution method**, performed via a pulmonary artery (Swan-Ganz) catheter, estimates CO by injecting a known volume of cold saline and detecting the resulting temperature change downstream. This technique remains widely used in ICU settings, though its use has declined with the rise of non-invasive monitoring technologies.
This calculator computes CO via either method and derives the cardiac index (CI = CO/BSA), stroke volume (SV = CO/HR), stroke volume index (SVI = SV/BSA), and systemic vascular resistance (SVR). These derived parameters provide a structured hemodynamic summary for education and case review.
Cardiac output and its derived parameters are useful for reviewing hemodynamic data in ICU and cardiology settings. This calculator keeps the relationships between the measurements visible so the output can be interpreted in context.
Fick Cardiac Output: CO = VO₂ / [(SaO₂ − SvO₂) × Hb × 1.34 × 10], where VO₂ = O₂ consumption (mL/min), Hb = hemoglobin (g/dL), SaO₂/SvO₂ = arterial/mixed venous O₂ saturation (fraction). Cardiac Index: CI = CO / BSA. Stroke Volume: SV = (CO × 1000) / HR. SVR = [(MAP − CVP) / CO] × 80.
Result: 5.14 L/min
With VO₂ of 250 mL/min, Hb 14 g/dL, SaO₂ 98%, and SvO₂ 75%, the arteriovenous O₂ difference is 4.31 mL/dL, yielding a CO of ~5.14 L/min (CI 2.71 L/min/m²), which is within normal range.
Fick calculations depend on oxygen consumption and saturation inputs, while thermodilution depends on catheter technique and repeatable injections. If the result looks unexpected, the first thing to check is whether the selected method matches the data you actually have.
Estimated VO2 values can be convenient but less precise than a measured VO2, and abnormal shunt physiology or severe valve disease can make derived values harder to interpret. Compare CO with CI, stroke volume, and SVR together so one number does not dominate the interpretation.
A low CO with high SVR suggests a different clinical picture than a low CO with low SVR. The value becomes more useful when read as part of the full hemodynamic profile rather than in isolation.
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This page calculates cardiac output from either direct Fick inputs or thermodilution-style inputs, then derives index values such as CI, SVI, and SVR. It is designed to make the relationships between those measurements visible for education and case review, not to replace a catheterization report or clinician interpretation.
Normal resting cardiac output in adults is 4–8 L/min. Cardiac index (CO divided by body surface area) of 2.5–4.0 L/min/m² is considered normal.
The Fick principle states that cardiac output equals oxygen consumption divided by the arteriovenous oxygen content difference. It requires measurement of VO₂ and arterial and mixed venous oxygen saturations.
Cardiac index normalizes CO for body size, allowing comparison between patients of different sizes. A CI < 2.2 L/min/m² indicates critically reduced cardiac function regardless of the patient's size.
Elevated SVR (> 1200 dyn·s/cm⁵) suggests increased afterload, seen in cardiogenic shock, hypertension, or hypothermia. Low SVR occurs in septic shock and anaphylaxis.
Normal SvO₂ is 60–80%. Values < 60% suggest inadequate oxygen delivery (low CO, anemia, or increased oxygen demand). Values > 80% can indicate sepsis or left-to-right shunts.
Both have limitations. Fick is considered more accurate at low cardiac outputs, while thermodilution may be more practical and reproducible. Significant tricuspid regurgitation can make thermodilution unreliable.