Comparison of bioimpedance and thermodilution methods for determining cardiac output: Experimental and clinical studies

The changes in electrical bioimpedance caused by the blood flow through a thoracic segment may be measured using a series of electrodes placed at opposing ends of this segment. Cardiac output (CO) is calculated by computer as the change in bioimpedance over time. This study was performed to determine the accuracy of bioimpedance CO (CObi) compared with standard thermodilution CO (COtd) in an animal model and in patients. COtd was determined using a thermodilution CO computer, and CObi was calculated with a bioimpedance computer in 10 dogs at baseline and at 5-minute intervals following the injection of 7 mEq of calcium chloride. A high correlation between COtd and CObi was observed (r = 0.91, p < 0.001) over a range of 2.5 to 6 L/min. Thirty-three paired observations using the CObi and COtd methods were performed in 10 patients following elective coronary artery bypass surgery. A significant correlation between the two methods was determined with a CO range of 2.1 to 7.8 L/min (r = 0.77, p < 0.001). CObi became inaccurate with severe tachycardia (pulse, 180/min), low CO, or frequent arrhythmias. These results indicate that this technique provides a continuous noninvasive method of determining CO that is comparable with thermodilution techniques. The technique of CObi holds promise for widespread use when continuous and noninvasive monitoring of CO is necessary.