Asploro Journal of Biomedical and Clinical Case Reports

Asploro Journal of Biomedical and Clinical Case Reports

Author(s): Wei Ma^1*
1Department of Anesthesiology, West China Hospital, Sichuan University, Chengdu, China

Corresponding Author: Wei Ma
Address: Department of Anesthesiology, West China Hospital, Sichuan University, Chengdu, Sichuan 611743, P.R. China.
Received date: 07 May 2026; Accepted date: 18 May 2026; Published date: 25 May 2026

Citation: Ma W. Research Progress on Anesthesia Depth Monitoring and Perioperative Neurocognitive Disorders in Elderly Patients. Asp Biomed Clin Case Rep. 2026 May 25;9(2):80-87.

Copyright © 2026 Ma W. This is an open-access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium provided the original work is properly cited.

Keywords: Electroencephalogram, Bispectral Index Monitor, Depth of Anesthesia, Perioperative Neurocognitive Disorders, Elderly Patients

Abstract

Perioperative neurocognitive disorders (PND) are highly frequent complications of the central nervous system in elderly patients and are closely related to trauma and neuroinflammation caused by anesthesia and surgery. However, the effect of the depth of anesthesia on PND remains unclear. Previous studies have shown that the use of electroencephalogram (EEG) monitoring to guide the management of anesthesia depth can reduce the dosage of anesthetic drugs and intraoperative awareness, but its preventive effect on postoperative cognitive dysfunction in elderly patients remains controversial. This review discusses the assessment of PND and its correlation with anesthesia and surgery. It also provides an overview of the effect of anesthesia depth monitoring on PND and its clinical application.

Background

Perioperative neurocognitive disorders (PND), the most common complication in surgical patients aged >65 years, encompass cognitive impairments occurring preoperatively or within 12 months postoperatively. These include pre-existing neurocognitive disorders, postoperative delirium (POD) within 7 days or before discharge, delayed neurocognitive recovery (DNR) persisting up to 30 days after surgery, and postoperative neurocognitive disorders extending to 12 months [1]. Studies report a PND incidence of 30%-65% in cardiac surgery patients. Among elderly non-cardiac surgery populations, the incidence approximates 30% at 1 week postoperatively and remains approximately 10% at 3 months [2]. Although most symptoms resolve in the short term, persistent or recurrent cognitive deficits occur in a subset of patients. These deficits not only impede postoperative recovery and prolong hospitalization but also profoundly affect long-term quality of life and survival outcomes [3]. PND significantly reduces patients’ functional independence, increases healthcare burden, and elevates mortality risk by 1.63-fold compared with unaffected individuals [4]. As society ages, elderly patients now comprise nearly 40% of surgical cohorts [5], making effective prevention of PND a critical issue in clinical anesthesia and perioperative management.

Anesthesia depth monitoring, as an important tool for assessing and regulating the degree of central nervous system inhibition, has attracted increasing attention in recent years because of its potential role in PND prevention strategies. Appropriate anesthesia depth management may be closely related to neurocognitive outcomes. Therefore, this article reviews current research progress on anesthesia depth monitoring and PND, aiming to provide references for optimizing anesthesia management and improving neurocognitive prognosis in clinical practice.

The Diagnosis of PND

To facilitate interdisciplinary communication and enhance clinical patient management, the diagnostic criteria for PND related to anesthesia and surgery are aligned with those for general neurocognitive disorders in the general population. Consequently, the diagnosis of PND continues to rely on the gold-standard criteria outlined in either the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), published by the American Psychiatric Association, or the International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10). However, applying the DSM-5 criteria presents challenges for non-psychiatric healthcare providers without specialized mental health training, as these criteria can be complex and nuanced. Therefore, neuropsychological tests serve as essential adjunctive tools for evaluating cognitive dysfunction. Such testing enables clinicians to detect surgery- and anesthesia-associated cognitive changes and subsequently diagnose PND according to DSM-5 or ICD-10 criteria.

To date, over 20 neuropsychological testing tools have been developed and validated for detecting cognitive impairment. Among these, the most widely utilized tools include the Mini-Mental State Examination (MMSE), the Montreal Cognitive Assessment (MoCA), the Confusion Assessment Method (CAM), and its ICU-adapted version, the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU). Research indicates that the MMSE demonstrates a sensitivity of 81% and specificity of 89% for distinguishing dementia patients from cognitively normal controls [6]. However, a limitation of the MMSE is its incomplete coverage of cognitive domains, particularly executive function. Notably, its specificity decreases to 65% and sensitivity to 63% when diagnosing mild neurocognitive disorders. Consequently, while the MMSE is suitable for rapidly screening moderate-to-severe cognitive impairment, it lacks adequate sensitivity for detecting mild cognitive impairment (MCI).

The MoCA, another extensively employed tool, also uses a 30-point scoring system [7]. Its key advantage lies in broader cognitive domain coverage, with a pronounced emphasis on executive function. Meta-analyses report a pooled sensitivity of 91% and specificity of 81% for identifying dementia, as well as 89% sensitivity and 75% specificity for detecting MCI [6]. Current guidelines strongly recommend the MoCA because of its high sensitivity and specificity in MCI detection and endorse its use for early screening.

The CAM is a simpler tool, typically requiring approximately 5 minutes for bedside delirium assessment while demonstrating high sensitivity (94%-100%) and specificity (90%-95%) [8,9]. The CAM-ICU, adapted for the intensive care setting, enables delirium detection in nonverbal ICU patients, including those receiving mechanical ventilation. It assesses behavioral responses to simple questions and visual/auditory identification tasks while maintaining excellent sensitivity (93%-100%) and specificity (98%-100%) [10]. However, existing cognitive tests still exhibit limitations in sensitivity and specificity, and no single neuropsychological test is universally accepted as the optimal method.

The Correlation Between PND and Anesthesia/Surgery

The pathophysiological mechanisms underlying PND remain incompletely understood [11-18]. Among these, the neuroinflammatory hypothesis is widely regarded as the predominant mechanism in PND pathogenesis. Surgically induced systemic inflammatory responses trigger neuroendocrine alterations that may damage synapses and neurons [19]. In elderly patients, age-related structural and functional decline of the central nervous system compromises resilience against perioperative inflammatory and oxidative stress, thereby predisposing this population to PND. Notably, whether specific anesthetic types or agents increase long-term cognitive disorder risk remains controversial.

Regarding the impact of different anesthesia types on postoperative PND, although regional anesthesia and nerve blocks may help mitigate the potential neurotoxic effects of general anesthetic agents, their effectiveness in reducing postoperative delirium and cognitive dysfunction has not been confirmed [20-22]. Some studies suggest that regional anesthesia does not interfere with cognitive function and may be safer than general anesthesia, with patients receiving general anesthesia exhibiting poorer cognitive function one week after surgery than those receiving regional anesthesia [23,24]. However, other studies have found no such difference [25,26]. Rasmussen et al. found no causal relationship between regional or general anesthesia and cognitive dysfunction, concluding that regional anesthesia offers no significant advantages [23]. Furthermore, no differences in cognitive function were observed at 3 or 6 months postoperatively between patients receiving general anesthesia and those receiving regional anesthesia [23,25].

Propofol and sevoflurane, as the most widely used intravenous and inhaled general anesthetic agents, respectively, have also attracted considerable attention regarding their potential roles in postoperative cognitive dysfunction. Previous studies have indicated that volatile anesthetic agents are associated with alterations in microtubule proteins and tau protein phosphorylation, potentially affecting cognitive function through β-amyloid accumulation, altered neurotransmission, and synaptic modifications, thereby increasing the risk of postoperative cognitive disorders [27]. Consequently, some studies have suggested that inhaled anesthetics may elevate the risk of postoperative cognitive disorders [28]. One study involving elderly patients under general anesthesia showed that those maintained on sevoflurane had a higher risk of neurocognitive disorders compared with those receiving propofol [29]. However, Konishi Y et al., who investigated the incidence of postoperative cognitive disorders in patients undergoing total hip arthroplasty under sevoflurane or propofol anesthesia, found no statistically significant difference in the incidence of postoperative cognitive disorders between the sevoflurane and propofol groups at 7 days, 3 months, or 12 months postoperatively [30]. Nevertheless, variations in the assessment methods used for postoperative cognitive dysfunction outcomes across these studies, along with potential confounding effects from other perioperative medications such as midazolam, dexmedetomidine, and nonsteroidal analgesics, may contribute to the discrepancies observed.

Anesthesia Depth Monitoring and PND

Anesthesia depth monitoring technologies, particularly quantitative indices derived from EEG signals such as the Bispectral Index (BIS), Patient State Index (PSI), and Entropy Index, provide essential tools for the objective assessment of anesthesia depth during the perioperative period. By applying proprietary algorithms to analyze complex raw EEG signals, these systems generate simplified, user-interpretable numerical indices, significantly lowering the threshold for EEG interpretation and aiding clinicians in the quantitative assessment of anesthesia depth. Previous studies have demonstrated that the use of anesthesia depth monitoring devices in adult surgical patients can reduce anesthetic drug consumption [31], help avoid intraoperative hypotension, and decrease end-organ toxicity associated with anesthetic agents [32,33]. Nevertheless, their role in preventing postoperative delirium and cognitive dysfunction remains controversial.

A growing body of evidence supports the potential benefit of EEG monitoring in reducing the risk of PND, particularly when maintaining a relatively lighter depth of anesthesia. Chan et al., who enrolled 921 elderly patients undergoing elective non-cardiac surgery, demonstrated that BIS-guided anesthesia resulted in a 21% reduction in propofol consumption and a 30% reduction in volatile anesthetic requirements compared with standard care without BIS monitoring. Importantly, the BIS-guided group exhibited a significantly lower incidence of postoperative cognitive disorders at 3 months postoperatively (10.2% vs 14.7%) [34]. This finding is supported by a meta-analysis showing a protective effect of BIS monitoring against cognitive dysfunction at 3 months postoperatively (15.8% vs 18.8%) [35]. Processed EEG-guided general anesthesia holds promise for tailoring sedative dosing to individual patient needs, potentially mitigating postoperative delirium symptoms. This approach is particularly important in frail elderly patients. Reflecting this emerging evidence base, several guidelines endorse EEG monitoring during general anesthesia in geriatric populations to help prevent early postoperative delirium [36,37]. Meanwhile, some studies suggest that, during anesthesia in elderly patients, the BIS value can be maintained at a relatively high level, namely 50-60 [38]. Maintaining lighter anesthesia may reduce the risk of postoperative cognitive dysfunction in elderly patients. Hou R et al. included elderly patients undergoing elective total knee arthroplasty and found that the risk of postoperative cognitive dysfunction was significantly lower in the BIS 55–65 group than in the BIS 40-50 group [39]. Another study involving elderly patients who underwent hip replacement surgery under general anesthesia combined with nerve block showed that the incidence of postoperative cognitive dysfunction was also lower in the BIS 60–80 group than in the BIS 40-60 group [35]. Some studies suggest that the use of BIS monitoring and maintenance of lighter anesthesia may reduce anesthetic drug exposure in elderly patients, thereby avoiding extremely low BIS values and reducing the impact on postoperative cognitive function [40]. However, it remains unclear whether the correlation between deep anesthesia and postoperative complications is caused by physiological effects such as impaired organ perfusion, altered immunity, or neuronal inhibition, or by the pharmacological effects of anesthetic drugs.

However, contrary evidence also exists. Some researchers suggest that deep anesthesia may exert neuroprotective effects by reducing brain metabolism and suppressing surgical stress responses [41]. A study involving 120 elderly patients undergoing general anesthesia for abdominal surgery found that the deep anesthesia group (BIS 35) had a significantly lower incidence of postoperative cognitive dysfunction 7 days after surgery than the light anesthesia group (BIS 50) (19.2% vs 39.6%) [42]. Similar conclusions were reported by An J et al., in which a lower BIS value (30-40) was associated with a significantly lower risk of postoperative cognitive dysfunction than a higher BIS value (55-60) (10% vs 27.5%) [43]. However, all of these studies were limited by small sample sizes and poor consistency in BIS maintenance between groups. Shi et al. included 4 studies involving 255 elderly patients in a meta-analysis. Low-level evidence suggested that the deep anesthesia group (BIS 30-40) had a lower risk of postoperative cognitive dysfunction after surgery. Differences in surgical procedures and anesthesia management among studies may have contributed to deviations in the results [44]. On the other hand, some high-quality studies have failed to demonstrate that EEG monitoring-guided anesthesia management is beneficial in preventing postoperative cognitive disorders. The ENGAGES study showed that the effect of EEG-guided anesthesia on the incidence of delirium within 1-5 days after surgery in elderly patients was not statistically significant [45]. Based on these findings, some current guidelines suggest that the available evidence is insufficient to recommend the routine use of processed EEG monitoring to reduce the risk of PND in elderly high-risk patients [46].

In conclusion, studies investigating the association between anesthesia depth monitoring and PND have yielded inconsistent results, which may be attributed to several factors, including differences in study populations, surgical types, and anesthesia protocols; inconsistencies in the definitions, assessment tools, and observation time points of PND; and the unclear mechanisms by which anesthesia depth affects cognitive function. Therefore, although EEG monitoring provides a powerful tool for achieving precise anesthesia, there is still no clear consensus regarding its routine use as a strategy for preventing PND. In the future, more rigorous and well-designed prospective studies with adequate sample sizes are required. Under standardized assessment systems, further exploration is needed to identify optimal anesthesia depth management strategies for different elderly subgroups and surgical scenarios, as well as to elucidate the underlying neurobiological mechanisms, ultimately guiding clinical practice.

Conclusion

PND is a common complication in elderly patients, and its occurrence is associated with multiple perioperative factors. Anesthesia management guided by EEG monitoring may be associated with a reduced incidence of PND, although the specific mechanisms remain unclear. At the same time, differences in the assessment criteria and methods used for PND across studies continue to pose challenges in clarifying its precise relationship with anesthesia depth monitoring. Although optimization of anesthesia depth management represents an important potential strategy for improving perioperative brain function in elderly patients, including “deep anesthesia” or “light anesthesia” strategies targeting specific BIS values, whether these approaches truly constitute controllable clinical variables still requires verification through more high-quality studies. As the number of elderly patients undergoing surgery continues to increase, maintaining cognitive health and promoting functional recovery through precise anesthesia management will remain an important direction for future clinical research and practice.

Conflict of Interest

The author has read and approved the final version of the manuscript. The author has no conflicts of interest to declare.

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