Fick Equation For Cardiac Output Calculator

Estimates the CO value in mL per min given oxygen consumption, arterial and venous concentrations.

You can read more about the measurements and the application of the Fick principle in the text below the calculator.


The Fick equation for cardiac output calculator uses the Fick principle of blood flow to determine the cardiac output. This method requires the measurement of arterial and venous oxygen content and the rate of oxygen consumption.

Cardiac output, or the amount of blood put in circulation by the contractions of the heart, during one minute, is a hemodynamic marker of cardiovascular efficiency.

High values may sometimes indicate infections while low values are often correlated with heart failure.


The three necessary variables for the calculation are:

■ VO2: oxygen consumption in mL/min;

■ Ca: oxygentated blood concentration;

■ Cv: venous blood concentration;

■ Ca - Cv: arteriovenous difference.

Fick formula is: CO = VO2 / (Ca - Cv)


Oxygen consumption (VO2):*
Oxygen concentration of arterial blood (Ca):*
Oxygen concentration of mixed venous blood (Cv):*
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About the variables used

The Fick equation for cardiac output calculator needs all of the following three measurements in order to determine the CO.

VO2 is the oxygen consumption measured by a spirometer in mL/min of pure gaseous oxygen. In practice, for this component, an assumed value is used because of the difficulty of real measurement. The most common forwarded value is based on the general rule of m2 of body surface area (BSA). Therefore, VO2 is considered as 125 mL/min, although this assumption has been long criticised as inaccurate.

Ca is the oxygen concentration of oxygenated blood (high oxygen content) collected at the situs of the pulmonary vein. In practice, a probe from peripheral arterial blood will be sufficient.

Cv is oxygen concentration of deoxygenated blood (low oxygen content) collected at the situs of an intravenous cannula.

The arteriovenous oxygen difference is derived from the difference between Ca and Cv. While heart and lung conditions do not affect the oxygen consumption, they affect the concentrations, thus leading to modifications of cardiac output.

 

Fick equation

The Fick principle observes that when blood flow is measured with a marker substance, the uptake and then release of substance, at the level of peripheral tissues, equals the product of the blood flow in that direction and the arterial-venous concentration difference (gradient) of the substance.

Therefore, the Fick equation can be written as:

VO2 = (CO x Ca) - (CO x Cv)

This leads to: VO2 = CO x (Ca - Cv) which in turn becomes:

CO = VO2 / (Ca - Cv)

When applying the Fick equation in practice, it is important to note the amount of marker substance taken up by the organ per unit time, concentration of substance in the arterial blood supply to the organ and in the venous blood leaving the organ.

 

References

1. Mahutte CK, Jaffe MB, Chen PA, Sasse SA, Wong DH, Sassoon CS. Oxygen Fick and modified carbon dioxide Fick cardiac outputs. Crit Care Med. 1994; 22(1):86-95.

2. Mahutte CK, Jaffe MB, Sassoon CS, Wong DH. Cardiac output from carbon dioxide production and arterial and venous oximetry. Crit Care Med. 1991; 19(10):1270-7.

3. Stock MC, Ryan ME. Oxygen consumption calculated from the Fick equation has limited utility. Crit Care Med. 1996; 24(1):86-90.


App Version: 1.0.1

Coded By: MDApp

Specialty: Cardiology

System: Cardiovascular

No. Of Variables: 3

Article By: Denise Nedea

Published On: March 16, 2017 · 10:04 AM

Last Checked: March 16, 2017

Next Review: March 10, 2018