THORACIC ELECTRICAL BIOIMPEDANCE MEASUREMENT OF CARDIAC-OUTPUT IN POSTAORTOCORONARY BYPASS PATIENTS

Objective: To assess the degree of correlation and agreement between c ardiac output by thermodilution and bioimpedance using the BoMed NCCOM 3-R7 monitor in postaortocoronary bypass patients. Design: Prospective , randomized sampling. Setting. Military teaching hospital intensive c are unit. Patients: Fifty patients undergoing coronary artery bypass s urgery with thermodilution pulmonary artery catheters in place. Simult aneous determination of cardiac output by thermodilution and thoracic bioimpedance was performed. Readings were taken between 8 and 24 hrs a fter surgery. Forty patients were intubated; 19 patients had left-side d tube thoracotomy in addition to two mediastinal tubes, and 19 patien ts 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 recei ving mechanical ventilation showed the best correlation (r2 = .40 and r2 = .45, respectively). Only 62% (31/50) of all patients had simultan eous measurements fall within 20% of each other, and there were no cli nical features that made identification of those patients possible. Co nclusions. Use of the BoMed NCCOM3-R7 bioimpedance monitor as a replac ement for thermodilution-derived cardiac output cannot be recommended in postaortocoronary bypass patients. The distortions of patients' nor mal anatomy and physiology, coupled with the presence of endotracheal tubes and mechanical ventilation, mediastinal tubes and chest tubes, r esult in only fair correlation, significant bias, and poor precision b etween the two measures of cardiac output.