Measurement of blood flow by thermodilution

Abstract

In thermodilution a known change in heat content of the blood is induced at one point of the circulation and the resultant change in temperature detected at a point downstream. When cardiac output is measured, a bolus of cool liquid is injected into the upper right atrium and the temperature change detected in the pulmonary artery. When flow in single blood vessels is measured, the distance between the site of injection and the site of detection is small; therefore, mixing must be attained by the kinetic energy of the injectate. The continuous constant rate injection technique is most suitable for measurement of venous flow. Since the blood flow in arteries can be markedly and unpredictably altered by the injection or the injectate, this technique is not suitable to measure flow in arteries. Measurement of venous flow by the bolus injection technique is tedious and time-consuming because of the complex formula. Minimal recirculation, simple and accurate calibration, intravascular detection of temperature and simple equipment are the advantages of the thermodilution technique.