How this calculator works
Fick flow equals whole-body oxygen consumption divided by the arterial-to-mixed-venous oxygen content difference. Use truly mixed venous blood and appropriately timed measurements. The gas-content option uses 1.34 mL O₂/g haemoglobin and dissolved oxygen 0.0031 mL/dL/mmHg. Measured uptake is preferred; the selectable 125 mL/min/m² estimate can introduce substantial error. Mosteller BSA provides the indexed output. The result is an estimate for information only and is not medical advice.
Formula
C_O₂(mL/dL) = 1.34 × Hb(g/dL) × saturation(fraction) + 0.0031 × PO₂(mmHg). CO(L/min) = VO₂(mL/min) / [10 × (CaO₂ - CvO₂)]. CI = CO/BSA.
Worked example
Oxygen uptake 250 mL/min with contents 20 and 15 mL/dL gives output 5 L/min. At BSA 2 m², cardiac index is 2.5 L/min/m².
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Frequently asked questions
Can I substitute a peripheral venous sample?
No. The Fick calculation requires a representative mixed venous sample; peripheral venous content is not interchangeable.
Why multiply the content difference by 10?
It converts oxygen per decilitre to oxygen per litre of blood.
Is estimated uptake as reliable as measured uptake?
No. The fixed body-surface estimate may be inaccurate during illness or altered metabolic states.