Anesthetic Considerations in the Geriatric Population

Issues of Concern

Physiologic Changes

Normal aging is associated with decreased reserve and function of all major organ systems limiting the available response to acute stress. Depending on many variables, including genetics, lifestyle, and preventative healthcare, the extent of each system's loss of function is highly variable. Proper assessment of each organ system's reserve should be obtained through history, physical, and focused diagnostic workup. Understanding patient physiology is vital to forming a safe and effective anesthetic plan.[3]

Cardiovascular

Decreased beta response limits the tachycardic response to hypotension in elderly patients. As a result, geriatric patients rely more on preload to maintain cardiac output. Additionally, baroreceptor reflexes become less sensitive with aging, limiting their maximum heart rate, stroke volume, and cardiac output in settings of decreased cardiac contractility and hypovolemia.[4]

Increased calcification, stenosis, and rigidity of arteries increase systemic vascular resistance and decrease compliance. As a result, elderly patients have wider pulse pressure and disproportionately large changes in blood pressure from small changes in preload and contractility. Labile hypertension commonly presents clinically as hemodynamic instability from dehydration, marked hypotension upon induction with intravenous anesthetic agents, and difficulty controlling postoperative hypertension. Patients may benefit from the coadministration of a vasopressor on induction to maintain blood pressure and coronary perfusion. Careful pain control and antihypertensives are often required postoperatively to avoid profound hypertension.[5]

Coronary atherosclerosis is not a component of normal aging and is rarely present in a healthy geriatric patient. However, elderly patients display a higher prevalence of coronary artery disease and are at higher risk for perioperative coronary ischemia. Left ventricular hypertrophy, widened pulse pressure with decreased diastolic blood pressure, and chronic hyperglycemia synergistically increases myocardial oxygen demand and decrease coronary perfusion. From the age of 65 to 86, the annual incidence of myocardial infarction in patients with no history of a cardiac event increases from 7.8 per 1000 person-years to 25.6, with higher risk associated with male sex, uncontrolled glucose levels, and poorly-treated hypertension.[6][7][8]

Decades of contracting against gradually increasing systemic vascular resistance cause concentric hypertrophic remodeling of the left ventricle. Poorly treated systemic hypertension and atherosclerosis accelerate the rate of hypertrophy. For this reason, geriatric patients are exceptionally reliant on cardiac filling and atrial kick and should not be subjected to tachycardia and arrhythmia. Left ventricular hypertrophy exposes patients to many high-risk comorbidities, including myocardial ischemia and diastolic heart failure.[9][10][11]

Physiologic stress to the aortic valve can result in pathologic calcification and thickening of the valve leaflets in elderly patients. Between 2% and 13% of patients over 65 have significant aortic stenosis, often undiagnosed. For non-urgent procedures, appropriate preoperative evaluation can guide anesthetic induction. As a significant number of geriatric procedures are urgent or emergent, obtaining an echocardiogram to evaluate the severity of aortic stenosis is not always feasible. Avoiding tachycardia and hypotension are general principles to improve coronary perfusion and avoid myocardial ischemia in older patients.[12][13]

Aging of the cardiac conduction system increases the incidence of ectopic beats and is a risk factor for many arrhythmias independent of other pathologies. Most age-related arrhythmias develop gradually due to fibrotic changes, inhibiting conduction pathways and promoting re-entry. Depending on where along the cardiac conduction pathway fibrotic remodeling is most significant, premature atrial and ventricular complexes, atrioventricular blocks, or bundle branch blocks can complicate the care of geriatric patients. Atrial fibrillation is the most common arrhythmia, with approximately 13% of the US population diagnosed by the age of 80. Atrial fibrillation more commonly develops secondary to diastolic dysfunction as left atrial dilation and fibrosis delay and disrupt conduction from the sinoatrial node to the atrioventricular node.[14][15]

Additionally, elderly patients often have atypical or asymptomatic presentations of atrial fibrillation, with some studies increasing detection and diagnosis by 33% with EKG screening. Naturally, elderly patients commonly rely on pacemakers or implanted defibrillators which may benefit from interrogation and setting optimization before surgery. Patients with atrial fibrillation are also commonly on chronic blood thinners due to the increased risk of stroke. In surgical and trauma settings, this can translate into increased blood loss and hemodynamic instability.[16]

Pulmonary

Nearly half of all perioperative deaths in geriatric patients are related to pulmonary complications. Decreases in immune function and loss of physiologic reserve make pulmonary optimization vital to prevent hypoxia, hypercarbia, and pneumonia. The pulmonary system and thorax undergo many gradual age-related changes, which steadily decrease function and reserve. Mechanically, patients experience increased work of breathing. The chest wall stiffens, the diaphragm flattens, and intercostal muscles weaken, all of which decrease inspiratory capacity. These changes place elderly patients at high risk of respiratory fatigue, especially in the setting of residual neuromuscular blockade and opioid use.[17]

At the parenchymal level, age-related lung changes mimic those of emphysema. Alveolar airspace and physiologic dead space increase while surface area decreases, inhibiting gas exchange and causing a ventilation-perfusion mismatch. The functional residual capacity decreases while the closing capacity increases resulting in earlier closure of small airways, diffuse atelectasis, and shunting. These appear in pulmonary function testing as decreased forced expiratory volume (FEV1), decreased diffusion capacity of the lung (DLCO), and increased A-a gradient.[18]

Furthermore, aging causes blunting of central responses to hypoxia and hypercarbia, especially in COPD and other lung diseases, decrease respiratory drive up to 50%. As many as 75% of patients over 65 in the US have some element of decreased pharyngeal muscle tone and obstructive sleep apnea, which may, in part, explain this phenomenon. As expected, blunting of these responses is even more pronounced during sleep or lingering sedation following surgery. Many anesthetic adjuncts, such as opioids and benzodiazepines, can cause significant postoperative sedation and hypercarbia leading to altered mental status, reintubation, or even life-threatening arrhythmias.[19][20][21]

Finally, pulmonary risk factors for geriatric patients extend far beyond the post-anesthesia care unit. Older patients have weaker pharyngeal muscles and less effective upper airway reflexes, and coughing. Older patients are also commonly colonized with gram-negative bacteria and have difficulty clearing secretions at baseline, much less following general endotracheal anesthesia. Even under ideal conditions, these patients are at high annual risk for hospitalization and death from pneumonia. During anesthesia, these risks can be reduced by minimizing and fully reversing neuromuscular blocking agents, using opioids and other sedating medications conservatively, and neutralizing gastrointestinal contents preoperatively to minimize aspiration risks. Postoperatively, incentive spirometry and early ambulation can also decrease pulmonary complications.[22][20][21]

Neurologic

Neurologic function in older patients is of particular importance perioperatively. Normal and pathologic aging cause many changes within the central and peripheral nervous system, most of which increase susceptibility to medications and postoperative complications. The most well-studied change in pharmacodynamics is that of volatile anesthetics and minimum alveolar concentration. An elderly patient is reliably anesthetized with up to a 30% decrease in concentration than a young adult. Similarly, all IV anesthetics share similar dosing adjustments. Many medications have undesirable side effect profiles in elderly patients. When forming and executing an anesthetic plan, the consequences of these side effects should be considered. Common potentially inappropriate medications used by anesthetists include diphenhydramine, scopolamine, benzodiazepines, metoclopramide, meperidine, and non-steroidal anti-inflammatory drugs (NSAIDs).[2][23]

As the brain ages, it commonly loses brain volume, cerebrospinal fluid, and dendrite synapses. Functionally, this can cause memory loss, cognitive decline, sleep disorders, delirium, depression, and decreased neuroplasticity. The diagnosis of dementia becomes relevant when memory and cognition limitations become severe enough to limit normal daily activities. The prevalence of dementia sharply rises as patients age. Dementia is rarely diagnosed before the age of 65, while 60% of all patients are affected by the age of 90. Depending on the severity, dementia can present several challenges that subject these patients to higher risk. Incomplete or inaccurate medical history and medication lists can yield missed anesthetic considerations, and difficulty communicating pain can delay important diagnoses (for example, delayed recognition of pain associated with an acute abdomen). Dementia also increases the risk of delirium and postoperative cognitive dysfunction, discussed later in the article.[24]

As a final point, some have hypothesized that cerebral autoregulation is blunted in the elderly, placing these patients at increased risk for cerebrovascular events. However, several recent studies have brought this principle into question. As anesthetics generally decrease cerebral autoregulation, care is necessary to ensure cerebral perfusion and oxygenation, especially for patients with dementia at higher risk for postoperative cognitive complications.[19][25]

Renal

Although the rate at which functional nephrons decline under physiologic and pathologic stress varies, the glomerular filtration rate generally declines as patients age. Increased rates of diabetes, hypertension, and vasculopathy further decrease renal function. On average, the glomerular filtration rate decreases by one milliliter per minute per meter squared each year after the age of 40. Older patients are typically at increased risk of acute kidney injury secondary to nephrotoxic agents such as NSAIDs and IV contrast. Geriatric patients also have decreased response to renin, angiotensin, aldosterone, and vasopressin and may have difficulty with volume status, electrolyte abnormalities, and acid-base derangements.[26][27]

Aging also contributes to several physiologic changes that affect pharmacokinetics. A typical patient that is 75 years old has 20% to 30% less plasma and intracellular volume. Along with adipose stores that do not decrease as rapidly, these decreased volumes explain the larger volume of distribution for lipophilic agents such as propofol. Combined with a decreased clearing capacity of aging renal and hepatic systems, these changes decrease required doses of many medications and increase the duration of their effects.[28][29]

Endocrine and Metabolism

Similar to other aspects of aging, there is a wide range in endocrine function and metabolic changes as patients age. Generally, the average patient's weight begins to decline in the sixth decade of life. However, some patients retain muscle mass and weight as they age, dependent on genetics, diet, and activity. Consideration of a patient's endocrine reserve can be a valuable component of perioperative care.[19]

Malnutrition is a common issue in elderly patients and strongly correlates with perioperative morbidity and mortality. Depending on many physical, social, and emotional factors, malnutrition may present acutely as a sharp decline in daily caloric intake and unintentional weight loss, or chronically as a body mass index of less than 18. For elective surgeries, clinicians should perform a nutrition screening during surgical evaluation. However, for urgent procedures, this requires immediate consideration and evaluation by the anesthetist.[30]

Heat production, insulation, and the ability to thermoregulate commonly decline with age. Many common procedures in the elderly, such as exploratory laparotomy or surgical repair of a hip fracture, can result in significant blood and insensible fluid loss and limit the available surface area of forced-air warmers. Incorporating temperature goals into the anesthetic plan and keeping the patient's normothermic decreases serious complications, including dysrhythmias, infection, and delayed wound healing.[31]

Type 2 diabetes mellitus is an increasingly common and particularly complicating comorbidity in the aging population. More than 15% of elderly patients in the US have been diagnosed with diabetes mellitus. Depending on the extensiveness of the disease and the proactivity of glucose management, perioperative management can range from checking blood glucose several times during the case to planned admission to the intensive care unit. Patients with uncontrolled diabetes are at significantly higher risks for coronary and peripheral artery disease, chronic kidney and end-stage renal disease, peripheral neuropathy, autonomic dysfunction, neurogenic bladder, and gastroparesis. A detailed history and chart review can be valuable in assessing a patient's insulin resistance level. Uncontrolled glucose levels place patients at higher risks of wound dehiscence and infection, which are much more likely to cause significant complications or death in elderly patients. However, treatment with antihyperglycemic medications must not be too aggressive, as tight euglycemic goals are associated with increased rates of hypoglycemia and mortality.[32][33][34]

Preoperative Assessment

The geriatric preoperative assessment should follow sound principles of the general medical evaluation, with additional attention paid to several issues of significance. While the current American Society of Anesthesiologists (ASA) Physical Status score does not explicitly list age as a predictor of risk for adverse outcome, increased likelihood of serious pathologies contributes to a higher median ASA score for older patients. Age should not be used as an absolute cutoff for preoperative testing or to cancel a surgical procedure but should encourage a more thorough assessment with several unique focus areas. To further complicate assessing geriatric patients, higher rates of urgent surgery and nursing home care often prevent patient and anesthetic planning evaluation until the day of surgery.[35][36]

More than 20% of patients over 65 undergoing surgery have baseline cognitive deficits that place them at higher risk of worsened postoperative cognitive dysfunction. Screening for cognitive impairment on the day of surgery can be complicated. While all elderly patients would benefit from a formal neurocognitive assessment, limited time and availability of geriatricians necessitate a more practical approach in the perioperative setting. Brief Cognitive Screening Tools such as the Minicog or Mini-Mental State Examination (MMSE) are practical and efficient means to stratify and document underlying cognitive deficits. A Brief Cognitive Screening Tool should be used outside of emergent cases to anticipate and decrease the risk of postoperative delirium and cognitive dysfunction.[37][38][39][24]

First and foremost, assessment of capacity for medical decision-making is non-negotiable when evaluating geriatric patients. A patient may act and converse normally but must comprehend and have a rational discussion concerning their condition, treatment options, and risks associated with these options. If there is any question concerning a patient's capacity to make informed decisions concerning their treatment, the right thing to do is to seek additional help from colleagues and the patient's family to encourage shared decision-making that aligns with their values.[40]  

Frailty is a general characterization of a patient's decline in organ function and physiologic reserve, as well as the accumulation of comorbidities. Grip strength, weight loss, gait assessment, cognitive tests, and medical history (including recent falls) are typical variables measured as frailty indicators. In other words, frailty is a preoperative stratification of perioperative vulnerability and correlates to increased mortality, lengthier hospital admission, and discharge to a skilled nursing facility. Several validated screening tools show a correlation between frailty and poor clinical outcomes such as mortality and 30-day postoperative complications. Many frailty assessment tools are chosen and implemented at the hospital level, but an understanding of alternative frailty criteria allows for more accurate risk stratification in particular patient populations. As an example, frailty assessment tools that include grip strength may miscategorize a patient with an isolated upper extremity nerve injury in his or her dominant hand. Along with other information obtained during the preoperative evaluation, frailty assessment can guide anesthetic and surgical plans, plan postoperative admissions and discharges, and anticipate postoperative delirium. When correctly assessed, frailty should also be a sensitive indicator for the necessity of in-depth conversations concerning complication risks, likely outcomes, goals of care, and alternatives to surgery.[41][42][43]

There is no current consensus among routine preoperative testing guidelines for noncardiac surgery, regardless of patient age. For major surgeries with anticipated admission, clinicians obtain routine bloodwork before the procedure. Electrocardiograms (EKG) are less specific than ASA scores in predicting perioperative risk and should only be obtained to provide answers to specific clinical questions rather than for routine screening. Preoperative testing should be guided by the patient's comorbidities and anticipated surgical complications. Some screening tests, such as pulmonary function testing, endoscopy, and echocardiography, require coordination with multiple departments and require discussion days before surgery.[44][45][46]

Clinical Significance

Monitoring

Anesthetists should follow ASA Standards for basic anesthetic monitoring for every patient undergoing anesthesia. First and foremost, qualified anesthesia personnel should be present and vigilant throughout the surgery to monitor hemodynamic stability and adequate anesthesia and analgesia. Additional monitors to detect changes in oxygenation, ventilation, circulation, and temperature are essential for a safe and effective anesthetic. Evidence is lacking concerning the use of processed electroencephalogram (EEG), such as the bispectral index (BIS), and the incidence of postoperative cognitive disorder (POCD). However, evidence supports lower anesthetic doses decreasing postoperative delirium risk; some have hypothesized that processed EEG may improve the ability to titrate anesthetic dosage carefully. Monitoring decisions should be patient and procedure-specific, with little data supporting the general use of more invasive monitors. However, many common comorbidities in the elderly will predispose these patients to the need for invasive blood pressure monitoring and other non-standard monitors.[47][48]

Positioning

Aging is accompanied by significant musculoskeletal changes, nearly all of which increase the risk of nerve, joint, and skin injury. Oversight during initial patient positioning and neglect during intraoperative shifting can cause increased pain and infection risks. Stiff joints, particularly in the cervical spine, hips, and shoulders, can prevent optimal patient positioning. Avoid applying force against resistance to increase joint angles, and apply supportive cushioning to rigid extremities. Geriatric patients also have fragile skin and decreased peripheral circulation. When positioning a patient, take additional care to avoid causing skin tears and bruising, and apply extra padding to areas at risk for pressure ulcers, including the sacrum and heels.[49][50]

General Anesthesia

Changes in the dosing of volatile anesthetics have been discussed previously in this article, but there are several other considerations for older patients undergoing general anesthesia. First, a thoughtful airway management plan must be formed to intubate the patient safely. Geriatric patients are often edentulous, making mask ventilation more challenging, and have decreased cervical extension, impairing direct laryngoscopy. These patients also display a wide range of hypotensive responses to induction agents and hypertensive responses to laryngoscopy. Vasopressors and fast-acting antihypertensives should be available during induction to maintain safe and adequate blood pressure. During the maintenance and emergence phases of general anesthesia, tempered dosing and patience are valuable principles, as elderly pharmacokinetics and dynamics can delay the return of respiratory function and extubation.[51][52]

Neuraxial Anesthesia

Several aspects of geriatric care hint toward the overall utility of neuraxial anesthesia to improve outcomes for certain surgeries. One of the most common surgeries performed almost exclusively on elderly patients, repair of fall-related hip fractures, lends itself well to spinal anesthesia. Compared to general anesthesia, Neuraxial techniques are associated with fewer pulmonary complications in patients with lung disease. Decreased requirement of sedating medications may decrease the risk of postoperative delirium. Evidence supports decreased discharge to skilled nursing facilities following total hip replacement for patients undergoing spinal anesthesia rather than general anesthesia.[53][54][55]

Conversely, neuraxial anesthesia is not ideal for long surgeries, patients with anxiety, and patients who have difficulty lying comfortably in the required position for surgery. Regional techniques follow similar principles as neuraxial anesthesia. Preservation of pulmonary function and decreased sedation are ideal as long as the patient can safely and comfortably tolerate surgery. Neuraxial techniques are also relatively contraindicated in patients with coagulopathies (pathologic or from anticoagulant or antiplatelet medications), aortic stenosis, or hemodynamic instability secondary to hypovolemia. For regional anesthesia, relative contraindications may include anticoagulation, local tissue infection, and respiratory dysfunction for nerve blocks near the phrenic nerve (specifically interscalene and supraclavicular nerve blocks).[56]

IV Anesthetic Agents

As discussed previously, geriatric patients typically require lower doses of intravenous anesthetics due to altered pharmacodynamic response and decreased drug clearance. Care and precision should be taken when administering these medications, especially in the setting of an unsecured airway, as aggressive dosing can lead to apnea or aspiration. Propofol, in particular, requires only 50 to 70 percent dosing (bolus or infusion) relative to that of a younger patient to achieve the same effect. Etomidate is often a more favorable choice as an induction agent in elderly patients with decreased cardiac reserve or hemodynamic instability. Again, a small dose is required for these patients to achieve a similar effect, primarily due to decreases in clearance and volume of distribution. Ketamine may be a practical primary or adjunct agent in certain circumstances but is rarely used in older patients due to postoperative delirium. The bronchodilatory effects of ketamine can be valuable for patients with reactive airway disease or hemodynamic instability without coronary artery disease.[57][2][58]

Opioids

Elderly patients are at higher risk of opioid-induced apnea, with decreased hypoxic and hypercarbic respiratory drive to compensate for oversedation. Opioids are significantly more potent due to decreased clearance and increased neurologic sensitivity. Due to this increased potency and side effect profile, many physicians are hesitant to aggressively treat pain in elderly patients. Pain should be treated first with non-opioid analgesics, with escalating treatment to weak opioids, then strong opioids until the pain is adequately relieved. For geriatric patients, smaller initial doses should be prescribed and titrated up to meet requirements safely. Consideration should also be given to renal dysfunction, limiting the clearance of morphine and its active metabolite morphine-6-glucuronide. The use of morphine places patients with decreased renal function at risk of apnea. Meperidine should also be used with caution in geriatric patients as it significantly increases the risk of postoperative delirium.[59][60][61][62]

Neuromuscular Blockers

The availability of neurotransmitters and neuroreceptors decreases with normal aging, with a significantly profound decline in the setting of neurologic disease. This decrease often results in a prolonged duration of neuromuscular blockade for most agents. In the setting of respiratory dysfunction, these changes increase the risk of postoperative respiratory complications and reintubation. Neuromuscular blocking agents should be avoided or used sparingly in the elderly population, considering agents eliminated by ester hydrolysis or Hoffmann degradation (atracurium, cisatracurium, and mivacurium), as these agents do not prolong paralysis in geriatric patients. Furthermore, weaker pharyngeal muscles and reflexes place older patients at higher risk for aspiration pneumonia in the setting of even minimal residual neuromuscular blockade, so complete reversal should be verified before extubation.[63][64][65][66]

Fluid Management

Fluid management has been a problematic area of research in the general population and can be particularly challenging in elderly patients. Depending on cardiac and renal abnormalities, geriatric patients often have poor tolerance for hypervolemia and hypovolemia. To compound this issue, older patients frequently present for urgent surgery at either extreme in terms of volume status, ranging from fluid overload in the setting of congestive heart failure (CHF) to severe dehydration following a fall. Dehydrated patients may benefit from preoperative fluid resuscitation or drinking clear fluids up to two hours before surgery, while fluid overloaded patients may require hospital admission for diuresis to optimize surgical conditions. In general, moderate administration of crystalloids or colloids to maintain euvolemia and avoid CHF exacerbation, pulmonary edema, and dilutional coagulopathies is appropriate for most patients. Depending on cardiopulmonary comorbidities, lower thresholds for transfusion of blood products may also be beneficial.[67]

Postoperative Delirium and Cognitive Dysfunction

Postoperative cognitive complications are the most common complication in elderly patients but are often neglected in preoperative discussions and planning. Risk factors include underlying cognitive dysfunction, history of cerebrovascular accident, depression, advanced age >70 years old, alcohol use, poor functional status at baseline, and abnormal electrolytes including sodium, potassium, and glucose. The ASA developed the Brain Health Initiative to help improve postoperative cognitive dysfunction health literacy amongst practitioners. This accessible platform contains tools and resources for practitioners and medical centers to implement preoperative cognitive assessment and postoperative cognitive dysfunction prevention guidelines. An additional goal of this initiative is to describe and study postoperative cognitive dysfunction better. In the near future, changes in nomenclature will likely rename Postoperative Cognitive Dysfunction as Perioperative Neurocognitive Disorder (PND) and further classify conditions based on duration and magnitude as delirium, delayed neurocognitive recovery, and major or mild neurocognitive disorder. Inclusion in future iterations of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) may also improve perioperative neurologic outcomes.[68][69][70][71]

Mortality

Many different attempts and strategies have been undertaken to quantify morbidity and mortality risks in older patients in previous years. Most have discovered age to be an independent risk factor, along with the invasiveness of the surgery and baseline comorbidities. For outpatient surgery, a Medicare database review discovered a mortality rate of 0.23% on the day of surgery and a 0.66% 30-day mortality rate, with higher risk associated with ages over 85. For inpatient noncardiac surgery within the Veteran Affairs system, patients over the age of 80 had an 8% 30-day mortality risk, with a 5% increase in relative risk for each year over 80. Additional mortality risk factors include diagnosis of ischemic or nonischemic heart failure, emergency surgery, invasive surgeries (abdominal surgery, aortic aneurysm repair, and thoracic surgery), and delay in emergent surgical intervention. Even minor procedures such as colonoscopies and cataract surgeries place patients at significant risks, and thorough efforts should be taken to minimize complications.[72][1][73][74]

Enhancing Healthcare Team Outcomes

Anesthetic care of elderly patients is a challenging aspect of perioperative medicine. As patients with more comorbidities and physiologic changes require anesthesia for procedures, an interprofessional team with adequate training and excellent communication is vital to decreasing morbidity and mortality. The role of the interprofessional team may include anesthesiologists, surgeons, nurses, surgical technicians, geriatricians, palliative care physicians, pharmacists, chaplains, and more. Failure of the team in assessing the patient and forming a surgical plan to maximize benefits while minimizing risks can result in poor outcomes and preventable patient harm. Before the patient arrives in the procedure room, assessments by team members should focus on determining the patient's physiologic reserve and be directed at cardiopulmonary risk factors, cognitive function, and common geriatric pathologies.[75] [Level I]

Intraoperatively, the surgical and anesthetic plans should minimize known risks for elderly patients. General anesthesia in geriatric patients is associated with acute respiratory failure, lengthier hospital stays, and higher mortality in hip fractures. Some studies suggest spinal anesthesia to be a safer primary anesthetic, but more research is needed to evaluate this hypothesis.[76] [Level II]

Finally, the incidence of Postoperative Cognitive Dysfunction is increasing each year. Early detection and thorough postoperative assessment of cognition changes should be a joint effort by physicians and nurses. Guidelines should be implemented at the institutional level and taught to all perioperative employees to improve neurologic outcomes.[77] [Level I]