Objective: To assess the degree of agreement between impedance cardiography, using the NCCOM3-R7 device, and the gold standard--the dye dilution method--both under basal conditions and after stimulation of cardiac output.
Patients: 35 paired measurements in five healthy male volunteers.
Interventions: To obtain higher levels of cardiac output, cardiac performance was stimulated with a dopamine infusion.
Results: In 35 paired measurements, the mean of all the impedance values was higher than that of the dye dilution values, at 10.2 v 7.4 l/min (p < 0.0001). The mean discrepancy between the two methods was 3.3 l/min, and the mean bias -2.9 l/min, with limits of agreement of -9.0 and 3.2 l/min. A change in cardiac output could not adequately be predicted by the NCCOM3-R7. In 20 of 25 measurements obtained during continuous intravenous dopamine infusions there was a rise in dye dilution cardiac output (range 0.2 to 5.9 l/min). Neither the magnitude nor the direction of the change in dye dilution values corresponded with the change measured by impedance cardiography. The mean discrepancy here between the two methods was 1.8 l/min, and the mean bias -0.8 l/min, with limits of agreement of -4.9 and 3.3 l/min.
Conclusions: In healthy volunteers, impedance cardiography with NCCOM3-R7 is inadequate for assessing cardiac output when compared with the dye dilution method.