Impedance stroke volume compared with dye and electromagnetic flowmeter values during drug-induced inotropic and vascular changes in dogs.

Stroke volumes measured by impedance were compared with values obtained by dye dilution and an electromagnetic flowmeter (EMF) on 14 dogs during drug-induced changes in cardiac contraction strength and peripheral resistance changes. Grouping all data for a total of 305 points showed correlations between dye and EMF, dye and impedance, and EMF and impedance of 0.89, 0.68, and 0.72, respectively. Correlations for individual dogs between dye and EMF, dye and impedance, and EMF and impedance ranged from 0.60 to 0.99, -0.39 to 0.96, and -0.26 to 0.89, respectively. These data suggest that the use of impedance cardiac output measurements to make treatment decisions about individual patients could result in serious error.