Cardiac Output Calculator

About the Cardiac Output Calculator

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.

When This Page Helps

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.

How to Use the Inputs

1. Select the calculation method: Fick principle (requires VO₂ and arterial/venous saturations) or thermodilution (direct CO entry).
2. For the Fick method, enter oxygen consumption (VO₂), hemoglobin, arterial O₂ saturation (SaO₂), and mixed venous O₂ saturation (SvO₂).
3. Enter heart rate and body surface area for stroke volume and indexed calculations.
4. Enter MAP and CVP to calculate systemic vascular resistance.
5. Use presets for common clinical scenarios (normal, heart failure, sepsis, cardiogenic shock).
6. Review all derived hemodynamic parameters and compare against the reference table.

Example Calculation

Tips & Best Practices

• Assumed VO₂ values (typically 125 × BSA) are often used when direct measurement is unavailable, but these estimates can be inaccurate.
• In sepsis, SvO₂ may be misleadingly elevated despite tissue hypoxia due to microcirculatory dysfunction.
• Thermodilution averages should be taken from 3+ injections, discarding outliers.
• An acute drop in SvO₂ with stable hemoglobin often indicates declining cardiac output.
• Consider the entire hemodynamic profile — CO, CI, SVR, and filling pressures — rather than any single parameter.

Practical Guidance

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.

Common Pitfalls

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.

Interpreting the Profile

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.

Frequently Asked Questions

• What is normal cardiac output?

  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.

• What is the Fick principle?

  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.

• Why is cardiac index preferred over cardiac output?

  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.

• What does a high SVR indicate?

  Elevated SVR (> 1200 dyn·s/cm⁵) suggests increased afterload, seen in cardiogenic shock, hypertension, or hypothermia. Low SVR occurs in septic shock and anaphylaxis.

• What is a normal mixed venous oxygen saturation?

  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.

• Is thermodilution more accurate than the Fick method?

  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.