Reports of Investigation

Purpose: Cardiopulmonary bypass (CPB) is characterized by transiocation of intestinal endotoxin and subsequent endogenous production of the pro-inilammatory cytokine interleukin-6 (IL-6). Plasma lipid fractions, especially high density lipoproteins, bind and neutralize endotoxin and, therefore, inhibit endotoxin-induced macrophage cytokine production, including IL-6. Increased IL-6 plasma levels have been implicated in adverse consequences associated with CPB. Previous studies demonstrated large interpatient variability in IL-6 plasma levels after CPB. The purpose of this study was to evaluate the relationship between plasma lipid concentrations and the concentrations of IL-6 following CPB in humans. Methods: In a prospective study, a group of 15 patients selected to exclude variables known to influence post-CPB plasma levels of IL-6 (preoperative left ventricular ejection fraction >45%, similar durations of aortic cross clamping and total CPB time, similar temperature control during CPB, and avoidance of platelet transfusion and shed mediastinal blood reqnfusion), IL-6 was measured at baseline, one and 24 hr post-CPB. Results: Interleukin-6 plasma concentrations (mean --SD) increased at one (142 + 89 pg'ml -~, P < 0.05) and 24 (129 82 pg'ml -j, P < 0.05) hr post-CPB compared with baseline (I.5 -+ I pg'ml -~) concentrations. An inverse correlation was found between IL-6 plasma concentrations at one hour post-CPB and plasma cholesterol concentrations (r = -0.592, P = 0.02), high density lipoprotein (r = -0.595, P = 0.02), and low density lipoprotein (r = -0.656, P = 0 . 0 1 ) .