What is the Fick principle used for?

The Fick principle is used to estimate cardiac output by relating oxygen consumption to the difference between arterial and venous oxygen content.

What inputs are needed for a Fick cardiac output calculation?

A typical Fick cardiac output calculation needs VO₂, hemoglobin, arterial oxygen saturation, PaO₂, mixed venous oxygen saturation, and PvO₂. Height and weight can also be added to estimate cardiac index.

What does the Fick calculator estimate besides cardiac output?

Besides cardiac output, the Fick calculator can estimate arterial oxygen content (CaO₂), venous oxygen content (CvO₂), arteriovenous oxygen content difference, and optional cardiac index when height and weight are provided.

Why can the Fick method be inaccurate?

The Fick method can be affected by errors in VO₂ estimation, hemoglobin measurement, oxygen saturation values, and mixed venous sampling. Small errors in oxygen content inputs can produce large swings in calculated cardiac output.

Hemodynamics & oxygen delivery tool

Fick principle, oxygen content, and cardiac index guidance

Fick Cardiac Output Calculator

Use this Fick calculator to calculate cardiac output with the Fick principle using VO₂, hemoglobin, arterial oxygenation, and mixed venous oxygenation. This tool estimates CaO₂, CvO₂, arteriovenous oxygen difference, and optional cardiac index for bedside hemodynamic interpretation.

Related PulmTools guides and calculators: Mixed Venous Genius (SvO₂), Mastering ABG Analysis, ABG Interpretation Guide, and P/F Ratio & Oxygenation Index.

Open Calculator Open SvO₂ Tool Read ABG Guide

Core equation

VO₂ ÷ (CaO₂ − CvO₂)

Best for

CO, extraction, perfusion states

Optional add-on

Cardiac index by BSA

Calculator inputs

Free-text bedside entry for faster workflow. Type values directly instead of stepping from 0.

Free text fields

Results

Enter your values above and click Calculate Fick Output to generate results.

How to interpret the Fick cardiac output

The Fick equation estimates cardiac output by dividing oxygen consumption by the arteriovenous oxygen content difference. In practical terms, if the body is consuming a known amount of oxygen and you know how much oxygen is removed between arterial and venous blood, you can estimate how much blood the heart must be pumping each minute.

This is most clinically useful when you are trending shock states, evaluating perfusion, or comparing oxygen delivery (DO₂) against metabolic demand. Low cardiac output with a widening extraction gap may support cardiogenic shock or low-flow states, while high cardiac output can be seen in sepsis, anemia, pregnancy, or vasodilated states.

For oxygenation context, pair this with the P/F ratio tool or the A–a gradient calculator. For acid-base review, use the ABG Interpretation Guide.

Related PulmTools hemodynamic & gas exchange tools

Mixed Venous Genius (SvO₂) →ABG Analyzer →P/F Ratio & Oxygenation Index →A–a Gradient Calculator →Mastering ABG Analysis →Causes of Hypoxemia Explained →

Fick calculator FAQ

What is the Fick principle?

The Fick principle estimates cardiac output from oxygen consumption and the difference between arterial and venous oxygen content.

Why does the Fick cardiac output change so much with small input errors?

Because the equation depends on the difference between CaO₂ and CvO₂, small errors in hemoglobin, saturations, or VO₂ can create large swings in the final cardiac output estimate.

When should I use cardiac index instead of cardiac output?

Cardiac index is often more useful when comparing perfusion between patients of different body sizes because it normalizes cardiac output to body surface area.