Quantitative relationships between plasma beta-endorphin immunoactivity and hemodynamic performance in preoperative cardiac surgical patients

To quantitate the importance of cardiac dysfunction as a stimulus for plasma immunoactive beta-endorphin (iBE) secretion, we measured iBE and hemodynamic indices in 65 patients prior to anesthetic induction for coronary artery bypass grafting or valve replacement. Linear regression analysis for the group as a whole showed significant correlations between iBE and stroke index (SI), pulmonary artery wedge pressure (PCW), and right atrial pressure (RAP), but not mean arterial pressure (MAP). Two patient subgroups were identified (P less than 0.001 by F-test): those with low SI and high iBE, or those with high SI and low iBE (cutoffs at 40 ml/m2 and 35 pg/ml, respectively). Correlations between hemodynamics and iBE were always stronger within the low-SI than the high-SI subgroups. These correlations were greater for patients with coronary artery than with valvular heart disease. Cardiac output (CO) and cardiac index (CI) correlated with iBE in valve-replacement and coronary-grafting groups. These findings were not an artifact of impaired iBE clearance due to renal dysfunction. Our results quantitate the importance of hemodynamic dysfunction for iBE secretion, and indicate that this relationship is particularly strong when stroke index declines below 40 ml/m2.