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Cardiac Output Calculator (Fick Principle)

Assess cardiac function and shock states using Fick's method.

Input Parameters

Enter patient data to calculate cardiac output.

Clinical Context & Significance

The Fick Principle, proposed by Adolf Fick in 1870, is a foundational concept in hemodynamics. It states that the total uptake or release of a substance by an organ is equal to the product of the blood flow to that organ and the arteriovenous concentration difference of the substance.

The Formula

CO (L/min) = VO₂ / ([CaO₂ - CvO₂] × 10)

Where VO₂ is oxygen consumption and CaO₂ - CvO₂ is the arteriovenous oxygen content difference.

Clinical Implementation

While thermodilution is more common in current clinical practice, individual Fick measurements remain the "gold standard" when low-flow states or significant valvular regurgitation (e.g., tricuspid regurgitation) make thermodilution inaccurate.

Note: This calculator uses the DuBois formula for BSA and standard estimations for $VO_2$ if measured values are unavailable. Oxygen-related calculations use a constant of 1.34 mL/g for the oxygen-binding capacity of hemoglobin.

Hemodynamic Evaluation, Cardiac Output, and the Fick Principle

Physiological Principles & Clinical Context

In patients with acute heart failure, cardiogenic shock, or those weaning from CPB, assessing cardiac output (CO) is essential. The Fick Principle states that the rate of uptake of a substance (in this case, oxygen uptake by the lungs) is equal to the product of cardiac output and the arterial-venous concentration difference of that substance. By measuring oxygen consumption and the difference in oxygen content between arterial and mixed venous blood, cardiac output can be calculated non-invasively, providing a gold standard for metabolic-hemodynamic status.

Clinical Targets & Safe Ranges

  • •Normal Resting Cardiac Output: 4.0 to 8.0 L/min.
  • •Normal Resting Cardiac Index: 2.5 to 4.0 L/min/m².
  • •Mixed Venous Oxygen Saturation (SvO₂): 65% to 75% (reflects systemic oxygen extraction balance).
  • •Normal Systemic Vascular Resistance (SVR): 800 to 1200 dyn·s/cm⁵.

Mathematical Formulation

  • ƒFick Cardiac Output: CO (L/min) = VO₂ (mL/min) / [ (CaO₂ - CvO₂) × 10 ]
  • ƒSystemic Vascular Resistance: SVR (dyn·s/cm⁵) = [ (MAP - CVP) / CO ] × 80
  • ƒOxygen Extraction Ratio: OER (%) = [ (CaO₂ - CvO₂) / CaO₂ ] × 100

Academic & Clinical References

  1. Fick A. Ueber die Messung des Blutquantums in den Herzventrikeln. Verhandl d phys-med Ges zu Würzburg. 1870;2:XVI.
  2. Guyton AC, Jones CE, Coleman TG. Circulatory Physiology: Cardiac Output and its Regulation. Philadelphia: W.B. Saunders; 1973.