Cerebral oxygenation and processed EEG response to clamping and shunting during carotid endarterectomy under general anesthesia

Clamping and shunting during carotid endarterectomy (CEA) surgery causes changes in cerebral blood flow. The purpose of this study was to assess and compare, side by side, the cerebral oxygenation (rSO(2)) and processed electroencephalogram (EEG) response bilaterally to carotid artery clamping and shunting in patients undergoing CEA under general anesthesia. With institutional approval and written informed consent, patients undergoing CEA under general anesthesia and routine carotid artery shunting were recorded bilaterally, simultaneously and continuously with an rSO(2) and processed EEG monitor. The response of the monitors during carotid artery clamping and shunting were assessed and compared between monitors and bilaterally within each monitor. Sixty-nine patients were included in the study. At clamping the surgical-side and contralateral-side rSO(2) dropped significantly below the baseline incision value (-17.6 and -9.4 % respectively). After shunting, the contralateral-side rSO(2) returned to baseline while the surgical-side rSO(2) remained significantly below baseline (-9.0 %) until the shunt was removed following surgery. At clamping the surgical-side and contralateral-side processed EEG also dropped below baseline (-19.9 and -20.6 % respectively). However, following shunt activation, the processed EEG returned bilaterally to baseline. During the course of this research, we found the rSO(2) monitor to be clinically more robust (4.4 % failure rate) than the processed EEG monitor (20.0 % failure rate). There was no correlation between the rSO(2) or processed EEG changes that occurred immediately after clamping and the degree of surgical side stenosis measured pre-operatively. Both rSO(2) and processed EEG respond to clamping and shunting during CEA. Cerebral oximetry discriminates between the surgical and contralateral side during surgery. The rSO(2) monitor is more reliable in the real-world clinical setting. Future studies should focus on developing algorithms based on these monitors that can predict clamping-induced cerebral ischemia during CEA in order to decide whether carotid artery shunting is worth the associated risks. From the practical point of view, the rSO(2) monitor may be the better monitor for this purpose.