FICK CARDIAC OUTPUT COMPUTER

Typical Number in Hospital:

Cost Bands:

References: 9

One of the many important measurements undertaken during cardiac catheterization procedures is a calculation of the rate of blood flow from the heart (cardiac output) in litres/minute. This is often achieved by injecting an indicator material into the pulmonary artery from the tip of the cardiac catheter and detecting the concentration of this material as it passes through the peripheral arteries.

An alternative method which does not require an indicator to be introduced is the Fick method in which the indicator is oxygen. The rate of use of oxygen is determined by a spirometer in conjunction with a carbon dioxide absorber. The patient rebreathes the air from the spirometer and the total volume falls as oxygen is consumed, since the resulting carbon dioxide is absorbed in the soda-lime canister. At the same time, blood is sampled from the venous circulation (from the pulmonary artery) and from the arterial circulation (via a cannula in a peripheral artery) and the concentration of oxygen in the blood samples is determined using a cuvette oximeter. Flow rate is then calculated as follows:

F = dm/dt /Ca-Cv

where F is the blood flow in litres/minute, dm/dt is the consumption of oxygen in litres/minute, Ca is the arterial concentration of oxygen in litres/litre and Cv is the venous concentration of oxygen in litres.litre.

The oxygen consumption may also be calculated using a fibre- optic oximeter which can be passed directly into the vessels.