Blood pressure and brain injury in cardiac surgery: a secondary analysis of a randomized trial

OBJECTIVES: Brain dysfunction is a serious complication after cardiac surgery. In the Perfusion Pressure Cerebral Infarcts trial, we allocated cardiac surgery patients to a mean arterial pressure of either 70-80 or 40-50 mm Hg during cardiopulmonary bypass (CPB). In this secondary analysis, we compared selected cerebral metabolites using magnetic resonance spectroscopy hypothesizing that a postoperative decrease in occipital grey matter (GM) N-acetylaspartate-to-total-creatine ratio, indicative of ischaemic injury, would be found in the high-target group. METHODS: Of the 197 patients randomized in the Perfusion Pressure Cerebral Infarcts trial, 55 and 42 patients had complete and useful data from GM and white matter (WM), respectively. Spectroscopies were done preoperatively and on postoperative days 3-6. Cognitive function was assessed prior to surgery, at discharge and at 3 months. We predefined the statistical significance level to be 0.01. RESULTS: A postoperative decrease was found in GM N-acetylaspartate-to-total-creatine ratio in the high-target group [mean difference -0.09 (95% confidence interval -0.14 to -0.04), P = 0.014]. No significant differences were found in other metabolite ratios investigated in GM or WM. No significant association was found between changes in metabolite ratios and new cerebral infarcts, WM lesion score or cognitive dysfunction. CONCLUSIONS: A higher mean arterial pressure during CPB was associated with signs of impaired cerebral metabolism, though not at the predefined significance level of 0.01. No significant association was found between metabolite ratio changes and neuroradiological pathology or change in cognitive function.