Fick Cardiac Output Calculator

How does this Fick Cardiac Output calculator work?

This health tool determines the cardiac output value which is a hemodynamic measure of heart function, basically the volume of blood pumped by the left ventricle during one minute.

The formula used in the Fick cardiac output calculator is based on the Fick principle which assumes that the rate of blood flow is correlated with oxygen consumption.

However, as usually oxygen consumption samples are obtained through a more complex procedure, a simplified method of calculation has been devised.

This involves the calculation of oxygen content in arteries and veins through haemoglobin levels in the red blood cells and its oxygen saturation.

Cardiac Output = (125 ml O₂/min/m² * BSA) / [13 * Hb * (SaO₂ - SvO₂)] = O₂ consumption / Arteriovenous O₂ difference

While BSA is calculated through the following equation:

Body Surface Area (BSA) = 0.024265 * (Height in cm)^0.3964 * (Weight in kg)^0.5378

Example of a calculation

Let’s take the case of a person weighing 68 kg at a height of 176 cm. Their haemoglobin levels have been measured at 13.4 g/dL while arterial oxygen saturation is 98% and venous saturation is 58%.

Answer: Cardiac output = 3.269 mL/min

Cardiac output (CO)

This is the blood volume in millilitres pumped by the heart per minute and represents a function of heart rate multiplied by stroke volume. Heart rate is the number of beats per minute while stroke volume is the volume of blood in mL pumped during each beat.

Therefore the first equation that can be written is that:

Cardiac output = Heart rate * Stroke volume

At an average heart rate at rest of 70 beats per minute and a stroke volume of 70 mL, cardiac output will be 4,900 mL/min.

By taking in consideration that each person has approximately 5 L of blood in the circulatory system, this means that during a minute, at a resting pace, the heart manages to pump and circulate almost all of the blood in the body.

Cardiac output is one of the measures of how efficient the heart is in performing its functions, therefore heart failure is characterized by low CO while during infections or inflammation, an increase in CO is observed as the body is trying to fight the condition.

One of the calculation methods, the one present in the Fick equation calculator, accounts for:

■ VO₂: oxygen consumption in ml/min of pure gaseous oxygen, measured through a spirometer;

■ Ca: oxygen concentration of oxygenated blood taken from the pulmonary vein;

■ Cv: oxygen concentration of deoxygenated blood from an intravenous cannula.

and employs the formula:

CO = VO₂ / (Ca - Cv)

References

1) Fagard R, Conway J. (1990) Measurement of cardiac output: Fick principle using catheterization. Eur Heart J; 11 Suppl I:1-5.

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

3) Vincent JL. (2008) Understanding cardiac output. Crit Care; 12(4): 174.

4) Cuschieri J, Rivers EP, Donnino MW, Katilius M, Jacobsen G, Nguyen HB, Pamukov N, Horst HM. (2005) Central venous-arterial carbon dioxide difference as an indicator of cardiac index. Intensive Care Med; 31(6):818-22.