Thoracic electrical bioimpedance measurement of cardiac output in postaortocoronary bypass patients.

Objective: To assess the degree of correlation and agreement between cardiac output by thermodilution and bioimpedance using the BoMed NCCOM3-R7 monitor in postaortocoronary bypass patients.

Design: Prospective, randomized sampling.

Setting: Military teaching hospital intensive care unit.

Patients: Fifty patients undergoing coronary artery bypass surgery with thermodilution pulmonary artery catheters in place. Simultaneous determination of cardiac output by thermodilution and thoracic bioimpedance was performed. Readings were taken between 8 and 24 hrs after surgery. Forty patients were intubated; 19 patients had left-sided tube thoracotomy in addition to two mediastinal tubes, and 19 patients were obese.

Interventions: None.

Measurements And Main Results: The overall degree of correlation between the two measures was fair (r2 = .24). The bias and precision measurements were inaccurate as well (-0.33 +/- 3.14). Patients with normal body habitus or who were not receiving mechanical ventilation showed the best correlation (r2 = .40 and r2 = .45, respectively). Only 62% (31/50) of all patients had simultaneous measurements fall within 20% of each other, and there were no clinical features that made identification of those patients possible.

Conclusions: Use of the BoMed NCCOM3-R7 bioimpedance monitor as a replacement for thermodilution-derived cardiac output cannot be recommended in postaortocoronary bypass patients. The distortions of patients' normal anatomy and physiology, coupled with the presence of endotracheal tubes and mechanical ventilation, mediastinal tubes and chest tubes, result in only fair correlation, significant bias, and poor precision between the two measures of cardiac output.