Perioperative Neurocognitive Disorders in Older Adults: Mechanisms, Biomarkers, and Evidence-Informed Management.

Perioperative neurocognitive disorders (PNDs) encompass cognitive change identified before or after surgery. Postoperative delirium (POD) is an acute, fluctuating disorder of attention and awareness, whereas delayed neurocognitive recovery and postoperative mild or major neurocognitive disorder describe objectively assessed decline over longer intervals. This narrative review focuses on older adults undergoing noncardiac and cardiac surgery and examines neuroinflammation, blood-brain barrier dysfunction, neurotransmitter imbalance, oxidative stress, synaptic dysfunction, candidate fluid biomarkers, and electroencephalography (EEG) features, and evidence-informed management. Multicomponent prevention, medication review, mobilization, sleep support, and individualized anesthetic care remain the most defensible clinical strategies. EEG-guided anesthetic titration can reduce anesthetic exposure but has not consistently reduced POD. Blood biomarkers, machine-learning models, trial-by-trial neural variability, and noninvasive brain stimulation are promising research tools, but none currently replaces standardized clinical assessment or justifies routine mechanism-specific treatment.