The measurement of cardiac output in dogs by impedance cardiography with different electrode arrangements.

This study was performed to compare cardiac output (CO) values determined by means of impedance cardiography (ICG) with the conventional four-band electrode array and with different spot electrode arrays in anaesthetised dogs. CO values determined at end-expiratory apnoea with hand-calculation (ICG1) and during several respiratory cycles with a computer program (ICG2) were compared with values obtained via simultaneous thermodilution (TD) measurements. Changes in CO during isoproterenol infusion, bleeding and reinfusion were also studied by means of ICG1, using one of the spot electrode arrays and TD. Band voltage electrodes yielded a significantly lower CO, whereas spot electrodes on the left thorax gave a significantly higher CO than that measured with TD. In spite of the high correlation coefficients in the different electrodes arrays, the bias between ICG1 and TD, and that between ICG2 and TD CO in the SL1-SL8 and BN-BX electrode arrays showed differences statistically significant from zero. The percentage changes in CO measured with ICG1 in the SN-SX electrode array and TD during isoproterenol infusion, bleeding and reinfusion also showed a high correlation. These results indicate that band voltage electrodes can be replaced by the more convenient spot electrodes in certain arrays. Further CO may be measured during several respiratory cycles by using a computer program. Thus, ICG is a reproducible, non-invasive method for the measurement of CO in anaesthetised dogs.