Right ventricular end-diastolic volume as a measure of preload

Right ventricular (RV) end-diastolic volume index (RVEDVI) measured by a modified thermodilution pulmonary artery catheter has been proposed as an improved measure of cardiac preload, compared with pulmonary capillary wedge pressure (PCWP). This study compared the correlation of RVEDVI and PCWP with cardiac index (CI) to determine which parameter better reflected ventricular preload. Modified thermodilution catheters were placed in 38 critically ill patients. Hemodynamic parameters were recorded in these patients at 2- to 4- hour intervals for 1 to 7 days. Complete data sets (1,008) were obtained. Regression analysis was performed comparing PCWP, RVEDVI, RV ejection fraction (RVEF) to CI in the entire group and in individual patients. Because mathematical coupling may exist between RVEBVI and CI, the correlation between these variables was corrected for mathematical coupling using the method described by Stratton. Simple regression analysis of data from all patients, uncorrected for mathematical coupling, yielded a significant correlation between CI and RVEDVI (r = 0.60, p < 0.0001), RVEF (r = 0.37, p < 0.0001), and PCWP (r = 0.10, p < 0.001). Correction for mathematical coupling between RVEDVI and CI resulted in a minor change of the correlation coefficient to 0.56. In individual patients, a significant, uncorrected correlation (p < 0.05) was found between RVEDVI and CI in 27 of the 38 patients, whereas 11 patients had a significant correlation between PCWP and CI. RVEDVI correlated more closely with CI than did PCWP, even after correction for mathematical coupling. In both the group as a whole and in individual patients, RVEDVI was a better indicator of cardiac preload.