Cardiac output measurement by thermodilution: methodologic problems.

In clinical practice, thermodilution technique for cardiac output measurement is generally applied to the right heart (injection of a saline cold bolus in the right atrium, temperature measurement downstream in the pulmonary artery). This technique is well adapted to repetitive measurements using a single catheter. However, its validity is dependent on several methodologic requirements: quantitation of the indicator, control of the catheter's dead-space effect, conservation and mixing of the cold bolus, accurate measurement of small thermal gradients. Calculations from the thermal dilution curve must be adapted to possible baseline shifts. All these different methodologic aspects are studied. Several solutions (heat exchanger, automatic injection, calculation method) are proposed. Comparison between an automatic thermodilution device and dye dilution has been performed successfully.