Serum protein S100 as marker of postoperative delirium after off-pump coronary artery bypass surgery: secondary analysis of two prospective randomized controlled trials

Background: To investigate the predictive value of S100 (biochemical marker of neuroglial injury) for the occurrence of postoperative delirium (POD) in patients undergoing off-pump coronary artery bypass (OPCAB)-surgery. Methods: We enrolled 92 patients older than 18 years undergoing elective OPCAB-surgery. Serum-levels of S100 were determined at baseline (BL), end of surgery (EOS) and on the first postoperative day (PD1). Postoperatively, all-patients were evaluated daily until PD5 for the presence of POD using the confusion assessment method (CAM) or the confusion assessment method for the intensive care unit (CAM-ICU) for patients in the intensive care unit (ICU). Results: The overall incidence of POD was 21%. S100-values on PD1 significantly predicted the occurrence of POD during the later hospital stay [area under the curve (AUC)=0.724 (95% confidence interval (CI): 0.619-0.814); p=0.0001] with an optimal cut-off level of 123 pg mL(-1) (sensitivity 100%, specificity 44%). Below this value, the absence of POD was predicted correctly in 43.66% of patients without POD [negative predictive value (NPV) of 100% (95% CI: 88.8%-100.0%) -positive predictive value of 29.8% (95% CI: 18.4%-43.4%) and likelihood ratio (LR) of the negative result of 0.0]. Conclusions: S100-levels <123 pg mL(-1) measured on PD1 reliably rule out the development of POD after elective OPCAB-surgery. This finding warrants testing whether S100-levels could be used for a risk stratification of cardiac surgical patients and for the initiation of preventive measures against POD in patients with high postoperative S100-levels.