CNS Changes with Aging

Introduction

• The population of adults aged 65 and older is growing, and these patients are accounting for a growing share of surgeries. Age-related changes, comorbidities, frailty, and preexisting cognitive impairment increase vulnerability to perioperative complications.³
• A basic understanding of typical changes in the CNS is paramount for providing informed guidance on individualized anesthetic management in older adults and for potentially reducing postoperative neurocognitive complications^.1

Pathophysiology of CNS Aging

Characteristic morphologic, physiologic, and pathologic changes within the CNS can affect anesthetic management and postoperative outcomes.²

Structural and Functional Changes

• Progressive loss of neuronal density, synaptic connections, and regional brain volume, particularly in the prefrontal cortex and hippocampus, diminishes cerebral reserve and reduces neural plasticity, increasing susceptibility to perioperative insults.¹
• Cerebral reserve is a key determinant of resilience to aging. Higher education, complex occupations, and lifelong cognitive engagement enhance reserve and buffer against decline. Neuroimaging findings, such as atrophy or amyloid deposition, must therefore be interpreted with reserve, as patients with greater reserve may retain normal cognition despite pathologic changes.^3,4
• Age-related cerebrovascular change, such as endothelial dysfunction and impaired cerebral autoregulation, reduce cerebral blood flow and the brain’s ability to maintain adequate perfusion during fluctuations in blood pressure. These alterations can increase the risk of ischemia during periods of perioperative hypotension. Patients with cerebrovascular disease or chronic hypertension are particularly vulnerable. Close hemodynamic monitoring is essential to preserve cerebral perfusion and prevent neurologic injury.^1,2

Molecular and Cellular Changes

• Age-related declines in neurotransmitter synthesis and receptor density, especially in the cholinergic system, increase the brain’s sensitivity to anesthetic agents, predisposing older adults to oversedation, delayed emergence, and POD. Cholinergic deficits may amplify the negative cognitive effects of anticholinergic drugs.²
• Mitochondrial dysfunction, oxidative stress, and impaired autophagy reduce neuronal energy reserves, heightening older adults’ vulnerability to perioperative hypoxia, hypotension, and anesthetic neurotoxicity. In practice, intraoperative cerebral oximetry and close hemodynamic monitoring remain the most effective tools for assessing real-time cerebral perfusion and oxygenation.^2,5
• Clinically, anesthesiologists can mitigate these risks through age-adjusted dosing, avoidance of deep anesthesia, maintenance of cerebral perfusion pressure, and use of multimodal neuroprotective strategies (e.g., optimizing oxygenation, minimizing sedative exposure, maintaining normothermia, and controlling inflammation).¹

Pharmacologic Changes

• Older adults experience significant age-related changes in pharmacokinetics, including reduced hepatic and renal clearance, increased body fat, and decreased plasma protein binding. These factors prolong drug elimination and increase the volume of distribution for lipophilic anesthetics and sedatives.⁶
• In addition, pharmacodynamic sensitivity is heightened due to alterations in receptor density, neurotransmitter availability, and impaired homeostatic regulation within the CNS. As a result, anesthetic agents exert more potent and prolonged effects, leading to an increased risk of excessive CNS depression, hypotension, and delayed emergence.^2,6
• These physiological changes necessitate lower induction and maintenance doses, gradual titration, and close monitoring to prevent overdose and complications. Some drug classes (e.g., benzodiazepines, anticholinergics, corticosteroids) should be used cautiously in older adults due to their greater pharmacodynamic sensitivity and altered pharmacokinetics.²

Perioperative Anesthetic Considerations for the Aging CNS System

• Advanced age, frailty, and preexisting cognitive impairment are among the strongest predictors of adverse perioperative brain outcomes. A preoperative history should identify conditions such as pre-existing cognitive impairment, frailty, cerebrovascular disease, seizure disorders, multiple sclerosis, and autoimmune disease. The preoperative evaluation should also assess alcohol, tobacco, substance use, psychiatric comorbidities, sleep, nutrition, and prescription or over-the-counter medication misuse.
  • Use of validated tools such as the Mini-Cog or MoCA (cognition), Clinical Frailty Scale (frailty), and Beers Criteria (polypharmacy), can facilitate systematic risk identification.^1,3
• Medication reconciliation is essential for identifying polypharmacy and inappropriate drug use. Polypharmacy is strongly linked to delirium and prolonged recovery.³
• Regional or general anesthesia, and total intravenous anesthesia (TIVA) or inhalation agents, are acceptable for older adults. As of yet, randomized trials have not demonstrated a superiority of one technique (regional vs. general, TIVA vs. volatile) over the other for delirium prevention. Therefore, the choice of anesthesia should be guided by surgical requirements, patient comorbidities, and goals of care.³
• The minimum alveolar concentration of volatile anesthetics decreases by approximately 6–7% per decade after age 30, reflecting age-related reductions in anesthetic requirements. Age-adjusted dosing with gradual titration is recommended, ideally guided by depth-of-anesthesia monitoring such as electroencephalogram (EEG) or bispectral index to minimize the risk of postoperative neurocognitive complications. While processed EEG monitoring may help reduce delirium incidence in some studies, multicenter trials have produced mixed results, suggesting that patient vulnerability and baseline frailty may be more influential than anesthetic depth alone.^1,2
• Polypharmacy and exposure to potentially inappropriate medications (as defined by the Beers Criteria) should be minimized perioperatively, as these agents may be associated with increased risk of POD.⁷

POD

• POD has a wide range of incidence, 5–65%, in older adults.1 Its multifactorial etiology involves neuroinflammation, neurotransmitter imbalance (particularly decreased acetylcholine and increased dopamine), and cerebral hypoperfusion, all of which disrupt large-scale neuronal networks and precipitate acute cognitive dysfunction.
• The table below outlines key risk factors for POD across the preoperative, intraoperative, and postoperative phases. It summarizes targeted strategies to mitigate delirium through proactive screening, physiologic optimization, and nonpharmacologic interventions.^1,3,6
• Please see the OA summary on postoperative delirium in aging patients. Link