Non-invasive measurement of cardiac output: whole-body impedance cardiography in simultaneous comparison with thermodilution and direct oxygen Fick methods

Objective: To determine the reliability of whole-body impedance cardiography (ICG(WB)), with electrodes attached to wrists and ankles, in the measurement of cardiac output (GO) on the basis of simultaneous comparison with thermodilution (TD) and direct oxygen Fick (Fick) methods. Design: Prospective clinical study. Setting: A surgical intensive care unit at a university hospital. Patients: Thirty consecutive subjects undergoing a coronary artery bypass surgery were investigated preoperatively. Measurements: ICG(WB) derived CO was measured simultaneously with the TD and Pick methods to establish the biases and limits of agreement (LA) between the methods. Results: The results obtained by ICG, and the invasive methods showed good agreement. The bias and LA between COTD and COICG were 0.00 l/min; -1.37 and 1.37 l/ min, respectively, and were close to those obtained between COTD and COFICK, 0.32 l/min; 1.74 and -1.10 l/min. The bias and LA between the COFICK and COICG were -0.32 l/min; -2.24 and 1.60 l/min respectively. The repeatability value of consecutive single measurements for ICG(WB) (RVICG = 0.57 l/min) was much better than for the TD method (RVTD = 1.10 l/min). Conclusion: There was close agreement between the results of the three methods in the measurement of CO. In sedated preoperative patients the accuracy of ICG(WB) is within clinically acceptable limits and its repeatability is excellent. ICG(WB) provides a useful alternative to the TD and Fick methods in cases where the pressures supplied by the pulmonary artery catheter are not essential.