Exposure to Bacteroides fragilis endotoxin during cardiac surgery

Although endotoxemia has been observed during cardiac surgery, the identity of endotoxins to which patients are exposed is unknown. We tested the hypothesis that antibodies to Bacteroides fragilis (an anaerobic gut commensal and a common pathogen) decrease during cardiac surgery, thereby reflecting systemic exposure to this type of endotoxin. Serum anti-endotoxin antibody levels were measured in 55 patients during routine cardiac surgery at the following times: Preoperatively, Pre-CPB (immediately before initiation of cardiopulmonary bypass [CPB]), Pre-CPB+5 (5 min after initiation of CPB), and End (end of surgery). Antiendotoxin antibody levels were determined by using enzyme-linked immunosorbent assay. Total immunoglobulin M (IgM) levels were measured by using laser nephelometry and decreases in total IgM levels were used to control changes in antiendotoxin antibody levels attributable to hemodilution. Median (interquartile range) hemodilution corrected IgM anti-B fragilis antibody levels decreased by 12% (5%-20%) from Preoperatively to End of surgery (P < 0.001). In contrast, median hemodilution corrected anti-B fragilis antibody levels did not change significantly from Pre-CPB to Pre-CPB+5, validating the correction for hemodilution. Immunoglobulin G anti-B fragilis antibody levels and IgM and immunoglobulin G anticore antibody levels decreased similarly during surgery. Intraoperatively, levels of anti-B fragilis endotoxin antibodies decreased significantly out of proportion to hemodilution. These results suggest that cardiac surgical patients are exposed to B fragilis endotoxin. Implications: We prospectively measured hemodilution-corrected antiendotoxin antibody levels in 55 cardiac surgical patients. We observed significant decreases in hemodilution-corrected levels of antibody to both Bacteroides fragilis and the core of endotoxin.