Advanced bilateral EEG monitoring for neuroprotection in high-risk cardiac surgery: a successful case report of emergency ascending aortic replacement

Background: Aortic surgery involving circulatory arrest and unilateral cerebral perfusion may be associated with hemispheric differences in scalp-recorded electroencephalographic (EEG) activity that are not detected by standard intraoperative monitoring. Bilateral frontal EEG analysis may provide additional descriptive information on cerebral electrical patterns during these procedures. Case presentation: A 62-year-old woman underwent emergency repair for type A aortic dissection with selective right-sided antegrade cerebral perfusion under deep hypothermia. Bilateral frontal EEG monitoring showed a marked reduction in EEG activity during circulatory arrest. Post hoc quantitative spectral analysis revealed asymmetric broadband power changes between hemispheres during cooling and perfusion phases, with alpha/delta ratio (ADR) values decreasing below 0.2 bilaterally and a peak left-to-right ADR ratio of 2.3. These hemispheric spectral differences were not appreciable on raw EEG inspection or cerebral oximetry alone. Conclusions: Post hoc quantitative bilateral EEG analysis, particularly spectral power distribution and ADR trends, may reveal hemispheric differences in scalp-recorded EEG activity during aortic surgery that are not captured by standard monitoring techniques. These observations support the exploratory role of advanced EEG analysis in the intraoperative assessment of cerebral electrical activity under deep hypothermia and selective cerebral perfusion.