The Cardiovascular
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Cardiac output (Fick principle)

Cardiac output and index from arteriovenous oxygen difference.

Cardiac output (Fick principle)
Haemoglobin
Arterial O₂ saturation
%
Mixed venous O₂ saturation
%
Body surface area
m²
Complete the fields above to see the result.

When to use

  • Right-heart catheterisation, when thermodilution is unreliable — notably in significant tricuspid regurgitation, low output or intracardiac shunt.

Formula

CO = VO₂ / [1.36 × haemoglobin (g/dL) × 10 × (SaO₂ − SvO₂)]. Oxygen consumption is estimated here as 125 mL/min/m² × BSA.

Pearls and pitfalls

  • This uses an *assumed* VO₂; a directly measured VO₂ is more accurate, and the assumption degrades at extremes of age, obesity and critical illness.

References

  1. LaFarge CG, Miettinen OS. The estimation of oxygen consumption. Cardiovasc Res. 1970;4(1):23–30.