Neurophysiological signatures of latent brain vulnerability in perioperative neurocognitive disorders: integrating EEG, cerebral oximetry, and processed EEG.

Perioperative neurocognitive disorders (PND) remain difficult to prevent because conventional cognitive assessments may fail to capture brain vulnerability in patients who appear cognitively normal before anesthesia and surgery. This narrative review examines the potential role of objective perioperative neuromonitoring markers as complements to cognitive scales, focusing on electroencephalography (EEG), near-infrared spectroscopy (NIRS)/cerebral oximetry, and processed EEG/bispectral index (BIS). Evidence from perioperative studies and related neurophysiological literature suggests that reduced or slowed alpha activity, lower spectral edge frequency, altered theta-band activity, burst suppression, cerebral oxygen desaturation burden, rSO₂ variability, impaired autoregulatory responses, and prolonged deep anesthetic exposure may reflect different dimensions of perioperative brain vulnerability. EEG primarily provides information on cortical oscillatory dynamics, anesthetic sensitivity, and network recovery; NIRS/cerebral oximetry reflects oxygen delivery, perfusion-metabolism mismatch, and hemodynamic instability; and processed EEG/BIS offers a simplified index of anesthetic-depth exposure rather than an independent neurophysiological modality equivalent to raw EEG or NIRS. Their combined value therefore depends not on simple multimodal aggregation, but on integrated interpretation across baseline assessment, anesthetic induction, intraoperative maintenance, emergence, and early postoperative recovery. Current evidence is limited by heterogeneous PND definitions, device-dependent signal processing, baseline variability, and a lack of prospective trials testing monitor-guided interventions. As a narrative review without formal risk-of-bias grading, this synthesis is also vulnerable to study-selection bias. Accordingly, EEG, NIRS/cerebral oximetry, and processed EEG/BIS should be viewed as candidate objective markers for risk stratification and perioperative brain-vulnerability phenotyping, rather than as a validated early-warning system. Future studies should determine whether these signals can identify actionable vulnerability profiles beyond cognitive screening and guide individualized perioperative brain-protection strategies.