Cardiac Output Calculator — Fick Principle, Cardiac Index & Stroke Volume

How it works

Fick: CO (L/min) = VO₂ (mL/min) / [(CaO₂ − CvO₂) × 10], with CaO₂ − CvO₂ = 1.34 × Hb × (SaO₂ − SvO₂) (mL O₂/dL; dissolved O₂ ignored). Estimated VO₂ = 125 mL/min/m² × BSA. Otherwise CO = HR × SV / 1000. Cardiac index = CO / BSA; BSA (Mosteller) = √(height cm × weight kg / 3600).

The Fick principle says that oxygen taken up by the lungs equals blood flow times the arteriovenous oxygen content difference. In the catheter lab VO₂ is ideally measured; the common assumption of 125 mL/min/m² (indirect Fick) can be off by 25% or more, especially in critical illness. Normal cardiac output is about 4–8 L/min and normal cardiac index 2.5–4.0 L/min/m²; a cardiac index under 2.2 with signs of hypoperfusion is part of the definition of cardiogenic shock.

Worked example

Height 175 cm and weight 75 kg give BSA 1.91 m² and estimated VO₂ = 125 × 1.91 = 239 mL/min. With Hb 14 g/dL, SaO₂ 98% and SvO₂ 72%, the AV O₂ difference is 1.34 × 14 × 0.26 = 4.88 mL/dL, so CO = 239 / 48.8 = 4.89 L/min. Cardiac index is 2.56 L/min/m² (normal) and stroke volume at 75 bpm is 65 mL.

Sources: StatPearls — Physiology, Cardiac Output · StatPearls — Calculating Fick Cardiac Output

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