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 lead to functional brain asymmetries undetected by standard monitoring. Frontal EEG, analyzed bilaterally, can provide deeper insights into cerebral physiology. Case Presentation: A 62-year-old female underwent emergency repair for type A aortic dissection with selective right-sided antegrade cerebral perfusion under deep hypothermia. Bilateral frontal EEG monitoring revealed a progressive suppression during circulatory arrest. Post-hoc spectral power analysis showed an early transient right-sided suppression during cooling, followed by delayed relative downregulation of the left hemisphere toward the end of surgery. Alpha/delta ratio (ADR) dropped below 0.2 bilaterally, with a peak ADR left versus right ratio of 2.3. These findings were not appreciable on raw EEG or cerebral oximetry alone. Post-hoc spectral analysis revealed functional hemispheric asymmetries possibly related to cooling techniques, asymmetric anesthetic redistribution and metabolic inactivation that are not appreciable on raw EEG or cerebral oximetry alone. Our observations support a multifactorial mechanism of EEG suppression and shed light on the potential diagnostic value of bilateral quantitative EEG monitoring. Conclusions: Quantitative bilateral EEG—particularly ADR and spectral power trends—may uncover functionally relevant cerebral asymmetries during aortic surgery, offering a complementary tool to guide neuroprotective strategies beyond standard oximetry.