Background
Carotid stenosis is a frequent coexisting condition in patients undergoing Coronary Artery Bypass Graft (CABG) surgery. During cardiac surgery, acute hemodynamic changes can cause cerebral ischemia. When acute slowing of the Electroencephalography (EEG) develops because of cerebral ischemia, a profound reduction in Bispectral Index (BIS) is seen, although the depth of anesthesia does not change. We investigated the diagnostic value of bilateral BIS as an indicator of cerebral hypoperfusion during CABG surgery in patients with carotid artery stenosis and the incidence of left-right BIS differences.
Methods
Forty patients scheduled for elective CABG surgery were randomized into two groups according to preoperative Duplex carotid ultrasound; Group with Carotid Artery stenosis (CA-stenosis) ( = 23) and Group without stenosis (CA-normal) ( = 17). All patients underwent monitoring using bilateral BIS system. We analyzed BIS data at eight stages of the CABG procedure.
Results
Mean BIS values recorded from left and right hemispheres declined significantly in comparison to steady state of anesthesia in both groups (T2), ( < 0.0001 for both). In CA-stenosis group only, there were significant interhemispheric differences during AXC apply ( < 0.01). Average BIS values of right and left hemispheres and parallel to it, SEF data decreased significantly in both groups during initiation of CPB-T3, during AXC application-T4 and during AXC removal-T6 ( < 0.001). Intergroup comparison showed significant decrease in BIS values in CA-stenosis group when compared to CA-normal group during induction of anesthesia-T1 and during AXC apply-T4 (both  < 0.001) and during AXC removal-T6 ( = 0.04).
Conclusion
Our findings suggest that an acute decrease in BIS which represent abrupt slowing of the EEG, reflects acute cerebral hypoperfusion particularly when it accompanies acute hypotension, as long as the changes in BIS is not drug induced.