Multiple cardiac output measurements in man. Evaluation of a new closed-system thermodilution method.

Cardiac output estimates by a new closed-system automatic injection thermodilution method (COI-TD) were compared serially with the direct Fick technique (COFICK) and the standard open-system manual injection thermodilution method (COTD). Comparison with cardiac outputs determined simultaneously by the direct Fick technique in 100 measurements involving ten patients showed close agreement with the new closed system method using both 25 degrees C and 3 degrees C injectates. The cardiac output range was between 1.9 to 11.6 L/min. The open-system manual injection thermodilution method under identical conditions produced a wide scatter of measurements when compared to the direct Fick technique. Reproducibility of simultaneous COI-TD and COTD measurements was examined in quadruplicate. The reproducibility of measurements was within 1.9 percent with COI-TD and 5.9 percent with the COTD method using both 25 degrees C and 3 degrees C injectates. The COI-TD method eliminates the technical problems of recirculation, unstable indicator baseline changes, thermal continuity, and reproducibility encountered with the current COTD method. Analysis of cardiac output by the closed-system automatic injection thermodilution method provides a simple, rapid, reproducible, and highly accurate method for multiple cardiac output measurements suitable for use at the bedside.