THERMODILUTION CARDIAC OUTPUT COMPUTER

Typical Number in Hospital: 1

Cost Bands: 4

References: 3,6

Just as cardiac output can be estimated during cardiac catheterization by means of a dye dilution computer, the dilution of a bolus of saline at a different temperature from the blood may be used to produce the same result. A fine catheter is passed up into the heart through a vein. The tip of the catheter passes through the heart into the pulmonary artery where a thermistor mounted on the catheter senses the temperature. An opening in the catheter then lies in or near to the right atrium and a bolus (e.g. 5 ml) of saline is injected rapidly through this. It mixes with the blood in the heart and temporarily depresses the temperature in the right atrium. The cardiac output (in litres/minute) can be calculated from the area under the curve of temperature depression and a knowledge of the quantity and temperature of the saline.

This technique has an advantage over dye dilution methods since it can be repeated frequently to produces information about the changes in cardiac output which may occur during treatment. Such apparatus may be found in the intensive care department and in the cardiac catheter laboratory.

In addition to the special catheter (often a Swan-Ganz catheter), which may be intended for single use, the apparatus must include a thermistor amplifier and linearizer, and a small computer.