Delirium is likely the most well-known perioperative cognitive disorder. Delirium, an acute and fluctuating alteration in the level of consciousness and attention, has significant consequences for patients, families, and the health care system. The incidence of delirium is associated with increased mortality, cognitive and functional decline, increased duration of hospital stay, and greater health care costs (JAMA 2010;304:443-51; N Engl J Med 2012;367:30-9; Ann Surg 2017;265:647-53; JAMA Surg 2015;150:1134-40; Arch Intern Med 2008;168:27-32). Though the effect of delirium in the ICU population is well recognized, perioperative delirium and the broader spectrum of neurocognitive dysfunction are ongoing areas of study and potential targets for improvement.

Patients who develop neurocognitive deficits in the perioperative setting (a broad category called perioperative neurocognitive disorders) are categorized based on the onset and duration of deficits (preoperative vs. various durations postoperatively) as well as the nature of the deficits (fluctuating vs. persistent). Preoperatively, patients with changes to cognition (preexisting cognitive impairment) are at increased risk of postoperative cognitive dysfunction (POCD). POCD includes delirium within seven days of surgery (postoperative delirium), cognitive impairment up to 30 days after surgery (delayed neurocognitive recovery), and cognitive impairment that persists between 30 days to over one year postoperatively (neurocognitive disorders) (Anesth Analg 2018;127:1189-95).

POCD is common, occurring in 50% of older adult patients after major cardiac surgery and 20% after major noncardiac surgery. POCD is a common concern among older patients undergoing surgery, and it can result in anxiety, depression, and post-traumatic stress disorder (Int J Geriatr Psychiatry 2019;34:1070-7). Risk factors for POCD include advanced age, lower level of education as a marker of lower cognitive reserve, baseline cognitive impairment, higher ASA Physical Status score, and longer length of surgery or higher blood loss (Anesthesiology 2015;122:1224-34).

While the etiology of POCD is currently unknown, hypotheses include aberrant oxidative cellular metabolism causing neurotransmitter abnormalities and imbalance, stress response to surgery altering the hypothalamic-pituitary-adrenal axis resulting in the release of proinflammatory cytokines, perioperative neuroinflammation, and an acceleration or unmasking of underlying cognitive disorders. Intraoperative management is also thought to play a role in developing POCD, including both depth and type of anesthesia administered, though ongoing study is needed (Anesthesiol Res Pract 2020;2020:7246570).

Despite national and international recommendations for assessing cognitive ability for patients older than age 65, routine preoperative assessment of cognitive function still needs to be fully integrated into clinical practice (Br J Anaesth 2019;123:464-78; Eur J Anaesthesiol 2017;34:192-214). As such, many patients with preexisting cognitive impairments remain undiagnosed. Screening for preoperative cognitive impairments would allow for a more individualized discussion of perioperative risks (delirium, delayed neurocognitive recovery, increased length of stay, discharge to a skilled nursing facility). One challenge to consistent screening is the need for a universally accepted screening tool. Some of the more common brief exams include the Mini Mental State Exam, Mini-Cog, and the Montreal Cognitive Assessment. Ideally, patients identified on screening assessment would be referred to an interdisciplinary team for a comprehensive assessment to identify potential modifiable risk factors, including presurgical medication changes to reduce polypharmacy. In addition, anesthesia and surgical teams should be provided with information about the risk of POCD in their patient and any additional perioperative risks (for example, vascular dementia is associated with higher perioperative stroke risk).

While there is insufficient evidence to recommend a specific method of anesthesia in higher-risk patients, there are actions that may reduce the risk of POCD. Consensus and expert advice continue to recommend avoidance of medications with anticholinergic properties (diphenhydramine, promethazine, scopolamine), benzodiazepines, and corticosteroids. Since intraoperative hypotension has been linked to POCD, careful dosing of anesthetics and blood pressure monitoring may be helpful, with exact hemodynamic goals varying based on a patient’s comorbidities and individual physiological state. Similarly, hypoglycemia and dehydration can also increase the risk of postoperative delirium, and proper glucose management and fluid resuscitation should be attained. Lastly, avoiding excess depth of anesthesia may also reduce the risk of POCD, though this is still an area of ongoing research.

Similar to recommendations for preoperative screening, patients should be screened for postoperative delirium or cognitive dysfunction in the PACU or shortly thereafter. Though there is no universally accepted standard screening tool, the 4AT and 3D-CAM have been associated with high sensitivity and specificity for delirium (ASA Monitor 2023;87:27-8).

Patients who screen positive for delirium should be started on nonpharmacologic treatment bundles. While multiple bundles exist depending on the hospital and patient’s location (HELP, Hospital Elder Life Program, and the ABCDEF ICU bundle are two examples), consistent themes include reorientation, appropriate hearing, visual, and speech aids, appropriate sleep hygiene, and limiting polypharmacy (Crit Care Med 2018;46:1464-70; Am J Geriatr Psychiatry 2018;26:1015-33).

As anesthesiologists, our impact on patients over a relatively short time period in the OR can have wide-ranging effects on a patient’s recovery and function at home after surgery. A thorough understanding of the range of POCD, frequent assessment preoperatively and postoperatively for treatable cognitive deficits and delirium, avoidance of evidence-based medication triggers, and thoughtful intraprocedural care can greatly impact our collective patient population.