Tracking cardiac output by a saline dilution technique using esophageal catheter electrodes

This paper presents preliminary results of a study in which saline indicator dilution curves were obtained by measuring impedance dilution curves using a tetrapolar catheter-based electrode placed in the esophagus of anesthetized dogs. Cardiac output (CO) was calculated from the area under the impedance-derived saline dilution curve, and compared to CO calculated from the saline dilution curve obtained by a cylindrical external conductivity cell placed in an arterio-venous shunt. The results revealed an approximately two-third overestimation in CO determined using the esophageal electrodes. However, the esophageal impedance CO tracked CO determined by the conventional indicator dilution method very well. When the data were pooled, a cumulative correlation coefficient of 0.96 was obtained. Although the esophageal impedance CO method overestimates CO, it tracks changes in CO well. Further investigation is indicated to determine an optimal electrode configuration for the tetrapolar esophageal electrode.