Oversaturation Status of Reticuloendothelial System Following Cardiopulmonary Bypass

Abstract: In the past, it was generally believed that the phagocytic function of the reticuloendothelial system (RES) was depressed after cardiopulmonary bypass (CPB), but several investigators reported differing results. Therefore, this study was performed to determine the effect of CPB on RES function, experimentally and clinically. Six dogs undergoing CPB (CPB group) were compared with an identical number of dogs subjected to thoracotomy without CPB (control group). A lipid emulsion test was performed in all dogs before and after the surgical procedure to measure RES phagocytic function. Any ultrastructural changes in Kupffer cells were observed by electron microscopy. In both groups, the RES phagocytic index showed a significant decline after surgery. However, comparison of the 2 groups revealed that there was a significantly greater decrease in the CPB group (p < 0. 05). Electron microscopy of the Kupffer cells showed that the number of phagosomes, especially those containing deformed erythrocytes, increased after CPB. Twenty patients undergoing cardiac surgery requiring CPB (Group A) and 8 patients undergoing pulmonary resection (Group B) were studied. RES phagocytic function was determined 3 days prior to surgery and 3 days postoperatively using the lipid emulsion test. No significant difference was observed in the preoperative phagocytic indices between the 2 groups. The phagocytic function remained almost unchanged in Group A on the third postoperative day, compared with the preoperative value, but it increased significantly in Group B on the third postoperative day, compared with the preoperative value. The intergroup difference was significant on the third postoperative day (p < 0. 01). These findings suggest that phagocytic activities of RES are not depressed but stimulated by CPB and that the phagocytic ability of RES is saturated by formed microparticles after CPB, such as residual of hemolyzed erythrocytes, protein aggregates, and microbubbles, among others. “Depressed RES phagocytic function” after CPB may not be a proper expression of this situation. It should be considered that the status of RES function after CPB is not functionally depressed but functionally oversaturated.