Whole-body impedance cardiography in the measurement of cardiac output.

OBJECTIVE: To evaluate the reliability of whole-body impedance cardiography with electrodes on wrists and ankles in the measurement of cardiac output compared with the thermodilution method.
DESIGN: Prospective, clinical investigation.
SETTING: Surgical intensive care unit and operating room at a university hospital. PATIENTS: Simultaneous cardiac output measurements by thermodilution and whole-body impedance cardiography were performed in 74 patients undergoing a coronary artery bypass grafting operation.
INTERVENTIONS: None.
MEASUREMENTS AND MAIN RESULTS: A total of 97 triplicate, simultaneous cardiac output measurements were carried out with thermodilution and whole-body impedance cardiography: 74 measurements were conducted in patients who were awake and 23 measurements were conducted during anesthesia but before the commencement of surgery. The mean cardiac output difference (bias) between the two methods was 0.25 +/- 0.81 (SD) L/min; the limits of agreement (2 SD) were-1.37 and 1.87 L/min, respectively. The repeatability value (rv = 2.83 x SD) for whole-body impedance cardiography (rv = 0.46 L/min) was considerably better than for the thermodilution method (rv = 1.05 L/min). Whole-body impedance cardiography reliably detected cardiac output changes induced by head-up tilt before anesthesia, by anesthesia induction, and by intubation. Two factors predicted the between-methods stroke volume difference: hematocrit (correlation coefficient r = -.36, r2 = .13; p < .001); and body mass index (r = .29, r2 = .08; p < .01). Using the multiple linear regression equation for correcting the stroke volume by hematocrit and body mass index, the limits of agreement (2 SD) between the methods studied were reduced to +/-1.28 L/min for cardiac output and +/-0.72 L/min/m2 for cardiac index.
CONCLUSIONS: There was close agreement between whole-body impedance cardiography and thermodilution in the measurement of cardiac output in patients with coronary artery disease without cardiac shunts and valvular lesions. The repeatability of the impedance method was significantly better than the repeatability of thermodilution. Whole-body impedance cardiography can be recommended for the assessment of cardiac output and its changes in the resting state. Whole-body impedance cardiography is a feasible and handy method for noninvasive and continuous measurement of cardiac output.