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Here Q is the cardiac output of the heart, C a O 2 is the arterial oxygen content, and C v O 2 is the venous oxygen content. (C a O 2 – C v O 2) is also known as the arteriovenous oxygen difference. The Fick equation may be used to measure V̇O 2 in critically ill patients, but its usefulness is low even in non-exerted cases. [8]
Using this value in the above equation, the oxygen concentration of mixed venous blood is approximately 150 mL of O 2 per L. Therefore, using the assumed Fick determination, the approximated cardiac output for an average man (1.9 m3) is: Cardiac Output = (125 mL O 2 /minute × 1.9) / (200 mL O 2 /L − 150 mL O 2 /L) = 4.75 L/min
Major factors influencing cardiac output – heart rate and stroke volume, both of which are variable. [1]In cardiac physiology, cardiac output (CO), also known as heart output and often denoted by the symbols , ˙, or ˙, [2] is the volumetric flow rate of the heart's pumping output: that is, the volume of blood being pumped by a single ventricle of the heart, per unit time (usually measured ...
The arteriovenous oxygen difference is usually taken by comparing the difference in the oxygen concentration of oxygenated blood in the femoral, brachial, or radial artery and the oxygen concentration in the deoxygenated blood from the mixed supply found in the pulmonary artery (as an indicator of the typical mixed venous supply).
A pulse oximeter probe applied to a person's finger. A pulse oximeter is a medical device that indirectly monitors the oxygen saturation of a patient's blood (as opposed to measuring oxygen saturation directly through a blood sample) and changes in blood volume in the skin, producing a photoplethysmogram that may be further processed into other measurements. [4]
CO reflects the hemodynamic flow and hence the transport of oxygen; its clinical applications by non-invasive continuous hemodynamic monitoring are especially useful for some medical specialties like anaesthesiology, emergency care and cardiology, for example to prevent hypoperfusion and to guide fluid administration.
One shortcoming of measuring pulse oximetry alone is that administration of supplemental oxygen (ie. via nasal cannula) can delay desaturation in a patient if they stopped breathing, therefore delaying medical intervention. Capnography provides a rapid way to directly assess ventilation status and indirectly assess cardiac function.
Cardiac index is a critical parameter in evaluating cardiac performance and the adequacy of tissue perfusion. In healthy adults, the normal range of cardiac index is generally between 2.6 to 4.2 L/min/m². Values below this range may indicate hypoperfusion and are often seen in conditions such as heart failure, hypovolemia, and cardiogenic shock.