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 (CO) 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 Fick methods to establish the biases and limits of agreement (LA) between the methods. Results: The results obtained by ICG_WB and the invasive methods showed good agreement. The bias and LA between CO_TD and CO_ICG were 0.00 l/min; –1.37 and 1.37 l/min, respectively, and were close to those obtained between CO_TD and CO_FICK, 0.32 l/min; 1.74 and –1.10 l/min. The bias and LA between the CO_FICK and CO_ICG were –0.32 l/min; –2.24 and 1.60 l/min respectively. The repeatability value of consecutive single measurements for ICG_WB (RV_ICG = 0.57 l/min) was much better than for the TD method (RV_TD = 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. Received: 19 February 1997 Accepted: 14 August 1997