Tools That Help Identify the Vulnerable Brain

A comprehensive geriatric assessment (CGA) is a detailed and thorough examination of a patient’s medical comorbidities, medications, frailty, cognitive status, mental health, psychosocial support, and physical limitations. The CGA looks at how these components interact and how they can be optimized to improve the patient’s health. From a perioperative brain health perspective, a CGA develops a personalized plan that not only helps identify which patients may have vulnerable brains but also how optimization may be able to decrease the risk of perioperative neurocognitive disorders. Expert consensus (BMC Anesthesiol 2021;21:127). Prior negative studies may be due to the inclusion of robust subjects, who may not have substantial benefit from a CGA, in contrast to frail patients.

Frailty is a syndrome of decreased resilience to stressors. It can occur as a result of multiple medical comorbidities, polypharmacy, physical weakness, poor nutrition, and cognitive impairment. Once present, frailty can lead to a rapid decline in a patient’s physical, psychological, and cognitive health. Preoperative frailty in older surgical patients carries a two- to three-fold increased incidence of POD (Anesth Analg 2021;133:314-23). Expert consensus recommends screening older patients for frailty (Br J Anaesth 2021;126:423-32). There are a plethora of tools to identify frailty. In the perioperative space, the National Surgical Quality Improvement Project 5-factor frailty index is a useful and easily implemented tool, as the majority of the factors within each index are already routinely documented (Am Surg 2021;87:1420-25). Preanesthesia evaluations are the perfect opportunity to determine the presence of the five factors: hypertension, COPD or recent antibiotic-treated pneumonia, diabetes, congestive heart failure exacerbation within 30 days, and assistance with any activities of daily living. Alternatively, the Clinical Frailty Scale is a phenotypic scale that uses the gestalt of the examiner to qualify the patient between fit to severely frail (BMC Geriatr 2020;20:393). It can be integrated into in-person assessments, but this method has limitations in the perioperative setting when many preanesthetic evaluations are performed over the phone or virtually. The FRAIL scale is another method that does not need in-person evaluation and can be given as a questionnaire to the patient to fill in on their own (J Nutr Health Aging 2008;12:29-37). It assesses five components of frailty: fatigue, resistance, ambulation, illnesses, and loss of weight. Whichever frailty screening is chosen, it should facilitate preselection of patients who then may benefit from a preoperative CGA and targeted interventions. A preoperative CGA offers the opportunity to optimize medications, comorbidity treatment, and nutritional status with the goal of reducing the patient’s risk of postoperative complications, including POD. Cognitive impairment often coexists with frailty and can also be quickly screened. However, most screening methods do require in-person or virtual video assessments, and few studies have shown how to do this on a large scale. Most of the brief cognitive screeners are shortened neurocognitive screens, such as clock drawing, three-word memory recall, or counting backward from 100 by seven. Ideally, if a patient screens positive for possible cognitive impairment, they would then be referred for a CGA. Even if a CGA is not obtained for frail or cognitively impaired patients, alerting the perioperative team of the patient’s frailty and vulnerability may improve vigilance and compliance with delirium prevention best practices.

Processed EEG (pEEG) monitors are commonly used by anesthesiologists to monitor depth of anesthesia. The integration and interpretation of the EEG in the perioperative period has the potential to improve brain health and should have a role in CGA implementation. EEG features such as processed indexes, burst suppression ratio, EEG waveforms (δ, θ, α, β, and γ waves) and their power, spectral analysis such as spectral edge frequency parameters and entropy features, among other elements, can hold valuable information representing perioperative vulnerability (Anesthesiology 2020;132:1003-16). Overall EEG power is diminished in the older patient, including decrease in alpha and delta power (Br J Anaesth 2015;115:i46-i57). Since pEEG indexes rely in part on the power of these two waves, algorithms misinterpret this phenomenon as a superficial anesthetic depth or low hypnotic plane. In addition, aging causes other brain morphological changes such as reduction in skull conductivity capable of modifying EEG features that are not recognized by pEEG algorithms (Br J Anaesth 2015;115:i46-i57). Of course, to be clinically significant, it’s necessary to conduct a thorough evaluation based on the context of several different signals of risk (Neurotherapeutics 2023;20:975-00).

In an awake state, older patients exhibit lower occipital alpha power as well as gamma power (J Clin Anesth 2023;86:111058). Beta band power increases with aging, peaking around 60 years and subsequently decreasing (J Clin Anesth 2023;86:111058). Cognitive impairment impacts EEG features in a similar fashion as aging and was shown to be associated with reduced beta and gamma power (Br J Anaesth 2015;115:i46-i5; J Clin Anesth 2023;86:111058). Although preoperative pEEG was shown to predict POD in older patients, it was only when clinical variables considering cognitive impairment and comorbidity status were added that the model exhibited satisfactory predictive performance (Aging Clin Exp Res 2023;35:1531-9). Additionally, decreased beta and gamma power as well as lower spectral edge frequency were associated with POD (Anesthesiology 2024;140:979-89). Finally, older patients demonstrate increased tendency to develop intraoperative periods of burst suppression. In the vulnerable brain, periods of burst suppression are associated with adverse postoperative outcomes, such as perioperative neurocognitive disorders, and should be avoided.

We have a great opportunity as perioperative clinicians to make use of the tools and comprehensive examinations available to optimize outcomes for our older patients, including frailty screening, CGA, and emerging advents in EEG monitoring within the perioperative period. These interconnected tools provide clinicians with a more expansive view into the brain health of surgical patients, allowing for better-tailored anesthetic care and management for vulnerable populations.