WHOLE-BODY IMPEDANCE CARDIOGRAPHY IN THE MEASUREMENT OF CARDIAC-OUTPUT

Objective: To evaluate the reliability of whole-body impedance cardiog raphy with electrodes on wrists and ankles in the measurement of cardi ac output compared with the thermodilution method. Design: Prospective , clinical investigation. Setting: Surgical intensive care unit and op erating room at a university hospital. Patients: Simultaneous cardiac output measurements by thermodilution and whole-body impedance cardiog raphy were performed in 74 patients undergoing a coronary artery bypas s grafting operation. Interventions: None. Measurements and Main Resul ts: A total of 97 triplicate, simultaneous cardiac output measurements were carried out with thermodilution and whole-body impedance cardiog raphy: 74 measurements were conducted in patients who were awake and 2 3 measurements were conducted during anesthesia but before the commenc ement of surgery. The mean cardiac output difference (bias) between th e 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/mi n) 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 anesthes ia induction, and by intubation. Two factors predicted the between-met hods stroke volume difference: hematocrit (correlation coefficient r = -.36, r(2) = .13; p < .001); and body mass index (r = .29, r(2) = .08 ; p < .01). Using the multiple linear regression equation for correcti ng 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/m(2) for cardiac index. Co nclusions: There was close agreement between whole-body impedance card iography and thermodilution in the measurement of cardiac output in pa tients with coronary artery disease without cardiac shunts and valvula r 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 cardiograph y is a feasible and handy method for noninvasive and continuous measur ement of cardiac output.