S100 protein and its relation to cerebral microemboli in on-pump and off-pump coronary artery bypass surgery.

OBJECTIVES S100 protein has been used as a marker for cerebral injury. Studies have reported lower levels in off-pump coronary artery surgery (CABG) compared to on-pump surgery. However, most of these are flawed as S100 from extracerebral sources was included (e.g. blood from cardiotomy suckers). Microemboli (high-intensity transient signals or HITS) during CABG have been implicated as a cause of postoperative neurocognitive dysfunction. The aim of this study was to compare the number of HITS during on-pump and off-pump CABG, measure S100 accurately by excluding extracerebral sources, and assess whether any changes in S100 were related to HITS. METHODS Thirty-five patients admitted for CABG were randomised to on-pump (n=20) or off-pump (n=15) surgery. Bilateral transcranial Doppler ultrasonography was performed on the middle cerebral artery to detect HITS. S100 was measured preoperatively, at termination of bypass in on-pump surgery, at completion of anastomoses in off-pump surgery, and 48 h postoperatively. A cell saver was used instead of cardiotomy suction in the on-pump group in order to limit extracerebral contamination of the S100 assay. RESULTS The number of HITS was 2016+/-1897 during on-pump and 16+/-21 during off-pump surgery (P<0.0001). In on-pump surgery S100 increased from 0.05+/-0.03 to 0.50+/-0.28 microg/l (P<0.0001) at termination of bypass. In off-pump surgery S100 increased from 0.08+/-0.05 to 0.35+/-0.20 microg/l (P<0.0001) at completion of anastomoses. The mean intraoperative S100 in the on-pump group was 1.6 times greater compared to that in the off-pump group (95% CI 0.88-2.8; P=0.01). There was no evidence of a relationship between S100 and HITS in both groups. By 48 h S100 decreased to 0.22+/-0.14 microg/l in the on-pump and 0.21+/-0.09 microg/l in the off-pump group (P<0.0001, compared to the preoperative value). CONCLUSIONS We have demonstrated a significantly higher number of cerebral microemboli in patients undergoing on-pump compared to off-pump CABG. By limiting contamination from extracerebral sources, we have shown S100 beta levels during on-pump CABG one and a half times greater than that in off-pump, although this did not reach statistical significance. In addition, we have shown no correlation between S100 beta and the total microemboli count, possibly because of the small numbers in this study.