Serum S100B levels in patients after cardiac surgery: Possible sources of contamination

Background: S100B protein is considered to be a potential marker of brain damage. The aim of our study was to determine the contamination effect of retransfused blood on the serum S100B concentrations in patients undergoing cardiac surgery with cardiopulmonary bypass (CPB) and to differentiate between this simple contamination effect and its possible enhancement by haemolysis. Methods: The first part of the study was performed in a group of 10 patients scheduled for coronary artery bypass grafting. Baseline S100B level was determined in a blood sample drawn from the radial artery before skin incision. After performing the distal anastomosis, additional blood samples were drawn from 1) the radial artery, 2) the aortic root catheter, 3) the pericardial space, and 4) CPB suction. To study the possible haemolytic effect on serum S100B levels, a second group of 23 patients was studied. S100B concentrations were determined in samples drawn simultaneously from the radial artery and bypass circuit after the end of CPB. Further samples from the retransfusion blood bag were analysed after one, two and three hours. Results: Blood samples from the pericardial space and CPB suction exhibited significantly higher levels of S100B than the samples drawn from the peripheral artery and aortic root catheter in the first group of patients. No significant differences between the S100B levels in the peripheral blood and aortic root catheter were detected. In the second group, S100B was significantly elevated in the samples taken from the retransfusion blood bag in comparison with peripheral blood. S100B levels remained stable during the whole follow-up period. Conclusion: The results of our study show increased serum S100B levels caused by contamination originating in the mediastinal tissues. Storage of blood in the retransfusion bag and haemolysis can be excluded as sources of contamination. The role of S100B in perioperative monitoring of patients undergoing cardiac surgery remains to be established and should be confirmed by further studies using neuropsychological tests and imaging techniques.