Pulmonary artery catheter vs. esophageal Doppler monitor: Measurement of cardiac output and left ventricular filling during cardiac surgery.

INTRODUCTION: Despite the risk of invasive hemodynamic monitoring, [1] management of cardiac surgical patients frequently mandates the measurement of cardiac output (CO) and left ventricular (LV) filling. [2] This study was designed to compare measurements of CO and LV filling using the pulmonary artery catheter (PAC) and esophageal Doppler monitor (EDM). METHODS: Following IRB approval and informed consent, 34 patients undergoing coronary bypass were instrumented with PAC and EDM. An electromagnetic flow probe (EM) was placed on the ascending aorta and was used as the "gold standard" for CO. In 20 patients, a transesophageal echocardiogram probe was placed and an end-diastolic cross-sectional short-axis image of the LV at the mid-papillary level was obtained (LV-EDA). LV-EDA served as the "gold standard" for LV filling. Prior to cardiopulmonary bypass (CPB), CO was measured from EM, EDM, and PAC (by thermodilution). LV filling was assessed from the PAC (as pulmonary artery diastolic pressure [PAD]), EDM (corrected flow time [FTc]) and LV-EDA. These measurements were repeated at 4 additional time points: 1) following a volume challenge of 400 mls; 2) following a second volume challenge of 400 mls; 3) 5 minutes post-CPB; and 4) 15 minutes post-CPB. For each subject concordance correlations were calculated over the five timepoints. To evaluate CO determinations, concordance correlations relating EDM to EM and PAC to EM were transformed using Fisher's z-transformation and compared using Student's t-test. To evaluate LV filling assessments, regression coefficients were created between the values of FTc and LV-EDA and between PAD and LV-EDA. Spearman correlations of these regressions were compared using the Wilcoxon rank sum test. A p-value of <0.05 was considered significant. RESULTS: The correlations between EDM CO and PAC CO with EM CO for all subjects at all timepoints are shown in Figure 1 and Figure 2. Concordance analysis revealed that EDM exhibited a closer affinity to EM than PAC for cardiac output, although the difference was not statistically significant (concordance correlations 0.55 +/- 0.08 vs. 0.49 +/- 0.08, mean +/- SEM, p=0.088). The correlation between FTc and LV-EDA was better than the correlation between the PAD and the LV-EDA (concordance correlation 0.49 +/- 0.12 vs. 0.10 +/- 0.10, mean +/- SEM, p<0.01).Figure 1Figure 2DISCUSSION: These data suggest that measurement of CO by EDM is at least as accurate as by PAC. This study further suggests that EDM FTc reflects changes in LV filling better than the PAD. Future studies evaluating this less-invasive technology appear warranted.