Cardiac Output
Calculate cardiac output using the Fick equation from height, weight, hemoglobin, and arterial/venous blood gas values. Free CO calculator with clinical interpretation and charts.
Arterial Blood
Venous Blood
About This Calculator
The Cardiac Output (CO) Calculator helps healthcare professionals, medical students, and patients assess cardiac function using the Fick principle, the gold standard for hemodynamic measurement. Cardiac output is the volume of blood pumped by the heart each minute, a critical parameter in diagnosing and monitoring heart failure, shock, and other cardiovascular conditions. By entering body measurements and blood gas values, you can calculate cardiac output, cardiac index, and oxygen content with clinical interpretation.
The calculation uses the Haycock formula for body surface area (BSA = 0.024265 × height^0.3964 × weight^0.5378), estimates oxygen consumption (VO₂ = 125 mL/min/m² × BSA), and computes arterial and venous oxygen content using the standard formula: O₂ content (mL/dL) = 1.34 × hemoglobin × (saturation/100) + 0.0031 × PO₂. Cardiac output is then derived as CO = VO₂ / ((CaO₂ − CvO₂) × 10), expressed in liters per minute. The cardiac index (CI = CO / BSA) normalizes the output for body size. Normal ranges are CO: 4–8 L/min and CI: 2.5–4.0 L/min/m².
Regional Notes
India: In Indian clinical practice, the Fick method is used in cardiac catheterization labs and intensive care units. Hemoglobin normal ranges in the Indian population are 13.0–17.0 g/dL for men and 12.0–15.0 g/dL for women. Blood gas analysis is widely available in tertiary care hospitals across metro and tier-2 cities.
United States: The Fick method remains the reference standard in US cardiology. The American College of Cardiology (ACC) and American Heart Association (AHA) guidelines recommend cardiac output monitoring in advanced heart failure management. Pulmonary artery catheterization (Swan-Ganz) is commonly used for direct measurement in ICUs.
United Kingdom: NICE guidelines recommend cardiac output monitoring in high-risk surgical patients and those in critical care. The NHS uses the Fick method alongside echocardiography for comprehensive hemodynamic assessment. Normal hemoglobin reference ranges in UK labs are 13.0–18.0 g/dL for men and 11.5–16.0 g/dL for women.
Frequently Asked Questions
What is cardiac output and how is it calculated?
Cardiac output (CO) is the volume of blood the heart pumps per minute. It is calculated using the Fick principle: CO = VO₂ / ((CaO₂ − CvO₂) × 10), where VO₂ is oxygen consumption (125 mL/min/m² × BSA), CaO₂ is arterial oxygen content, and CvO₂ is venous oxygen content. The normal range is 4 to 8 L/min.
What is a normal cardiac output range?
A normal cardiac output ranges from 4 to 8 L/min in healthy adults at rest. The cardiac index (CO divided by body surface area) should be between 2.5 and 4.0 L/min/m². Values below 4 L/min may indicate reduced cardiac function, while values above 8 L/min suggest a high-output state.
What is the Fick principle for cardiac output?
The Fick principle states that cardiac output equals oxygen consumption divided by the arteriovenous oxygen difference. Oxygen consumption is estimated as 125 mL/min per square meter of body surface area. Arterial and venous oxygen contents are calculated from hemoglobin, oxygen saturation, and oxygen tension using the formula: O₂ content (mL/dL) = 1.34 × Hgb × (Sat/100) + 0.0031 × PO₂.
What is the difference between cardiac output and cardiac index?
Cardiac output (CO) is the total volume of blood pumped by the heart in liters per minute. Cardiac index (CI) normalizes CO for body size by dividing it by body surface area (BSA). CI allows comparison between individuals of different sizes. A normal CI is 2.5 to 4.0 L/min/m², while normal CO is 4 to 8 L/min.
What blood tests are needed for cardiac output calculation?
The Fick method requires hemoglobin level and arterial and venous blood gas measurements including oxygen saturation (SaO₂, SvO₂) and oxygen tension (PaO₂, PvO₂). These are obtained from an arterial blood gas (ABG) and a venous blood gas (VBG) sample, typically drawn from a central venous catheter or pulmonary artery catheter.
How accurate is the Fick method for cardiac output?
The Fick method is considered the gold standard for cardiac output measurement in clinical practice, with an accuracy of approximately ±10% when properly performed. Direct measurement of oxygen consumption with a spirometer improves accuracy. This calculator provides an estimate; always consult a healthcare professional for clinical decisions.
What does a low cardiac output mean?
A low cardiac output (below 4 L/min) indicates the heart is not pumping enough blood to meet the body's oxygen demands. This can result from heart failure, cardiomyopathy, valvular heart disease, or hypovolemia. Symptoms include fatigue, shortness of breath, and reduced exercise tolerance. Immediate medical evaluation is recommended.
Can I use this calculator if I don't have blood gas results?
The Fick method requires blood gas values for accurate calculation. If you do not have blood gas results, consider using the Doppler echocardiography method for cardiac output estimation, which uses ultrasound to measure blood flow through the heart without invasive blood sampling.