Comparison of cardiac output determined by bioimpedance, thermodilution, and the Fick method.

BACKGROUND: Cardiac output can be determined by using a variety of methods.
OBJECTIVES: To determine the precision and bias between 3 methods for determining cardiac output: bioimpedance, thermodilution, and the Fick method.
METHODS: Cardiac output was determined by using bioimpedance via neck and thorax patches and thermodilution via pulmonary artery catheter in 46 patients in the intensive care unit. A subset of 15 patients also had cardiac output determined by using the Fick method.
RESULTS: Mean (SD) cardiac output in all patients was 6.3 (2.2) L/min by thermodilution and 5.6 (2.0) L/min by bioimpedance. In the 15 patients in whom all 3 methods were used, mean cardiac output was 6.0 (1.7) L/min by thermodilution, 5.3 (1.7) L/min by bioimpedance, and 8.6 (4.5) L/min by the Fick method. Bias and precision (mean difference +/- 2 SDs) were 0.7 +/- 2.9 L/min between thermodilution and bioimpedance, 1.7 +/- 3.8 L/min between the Fick method and thermodilution, and 2.4 +/- 4.7 L/min between the Fick method and bioimpedance.
CONCLUSION: Bioimpedance, thermodilution, and Fick determinations of cardiac outputs are not interchangeable in a heterogeneous population of critically ill patients.