Thermodilution cardiac output--a systematic error.

The purpose of this study was to examine the mechanism and magnitude of a systematic error in thermodilution cardiac output measurement. One hundred and seventy-one thermodilution cardiac output measurements in dogs using a Swan-Ganz catheter were compared with simultaneously made dye dilution measurements under different conditions over a wide range of cardiac outputs. A systematic error with the thermodilution technique was confirmed and was almost identical to that observed in the literature. It is proposed that its mechanism is loss of thermal indicator between the injectate orifice and detection. Application of a further correction factor for thermal indicator loss is suggested.