Neuroanesthesia: Preoperative Evaluation

This chapter includes an accompanying lecture presentation that has been prepared by the authors: .

Key Concepts

Timely preanesthetic evaluation is critical for safety of perioperative care, optimal resource utilization, improved outcomes, and patient satisfaction for the neurosurgical patient.
Effective preanesthetic evaluation obviates unnecessary “medical consultations.”
The preanesthesia clinic is a key component of the Perioperative Surgical Home model aimed to make surgical care safer and more efficient, and is essential for the success of Enhanced Recovery After Surgery (ERAS) to decrease postoperative intensive care unit admission while minimizing length of hospital stay, complications, readmissions, and health care costs.
The American Society of Anesthesiologists (ASA) classification of physical status is a universally accepted system for stratification of patients’ preexisting health status.
Focused preoperative evaluation of geriatric patients is a key aspect of the Perioperative Brain Health Initiative, a patients’ safety initiative to minimize the impact of preexisting cognitive deficits on outcome and optimize cognitive recovery of adults aged ≥65 years.
Preanesthetic evaluation of cognitive function and assessment of frailty are increasingly important, given the increasing number of older individuals requiring surgery.
The American College of Surgeons (ACS) National Surgical Quality Improvement Program (NSQIP) surgical risk calculator is a valuable tool to estimate the possibility of unfavorable outcomes after surgery ( http://www.riskcalculator.facs.org ).
The 2014 update of the American College of Cardiology (ACC)/American Heart Association (AHA) guidelines on perioperative cardiovascular evaluation provides a useful framework for preanesthetic evaluation of patients with preexisting cardiac conditions.

Preanesthetic evaluation is defined as the clinical assessment that precedes the delivery of anesthesia care for surgical and nonsurgical procedures. The primary aim of preanesthetic evaluation is to minimize overall patient morbidity associated with surgery and anesthesia. This is achieved by assessing the patient’s baseline medical morbidity and, to optimize the balance between the anesthetic risk and surgical benefit, by improving any correctable medical condition within the limitations of the surgical circumstances, in addition to formulating the best anesthetic plan. Other benefits include improved safety of perioperative care, optimal resource utilization, and improved outcomes and patient satisfaction. The American Society of Anesthesiologists (ASA) model of the Perioperative Surgical Home—a patient-centered, physician-led system of coordinated care—strives for better health care and reduced costs of care ( Fig. 7.1 ). Appropriate preoperative evaluation by anesthesiologists is a critical component of this model, which incorporates, among other things, efforts to reduce unnecessary interventions (e.g., routine preoperative laboratory studies) as well as efforts to reduce cancellations and length of postoperative hospital stays. Preoperative consultation with an anesthesiologist enhances perioperative care and outcomes and has the potential to further decrease the cost of unnecessary routine “medical consultations,” often driven by highly variable clinical and nonclinical factors. The broad objectives of preanesthesia evaluation include:

1.
Establishment of rapport with the patient and family members or significant others in order to minimize their anxiety and to have a cooperative and relaxed patient
2.
Provision of information regarding anesthetic techniques and procedures and the associated risks and benefits; postoperative management issues including pain control and possible need for postoperative mechanical ventilation after major procedures
3.
Complete review of medical, surgical and anesthetic history and current medications, thus establishing a baseline profile
4.
Review of relevant personal, family, and social history and history of allergies
5.
General physical examination including recording of vital signs and examination of individual systems, particularly the nervous and cardiopulmonary systems
6.
Interpretation of relevant laboratory data, arrangements for further investigations and consultations if deemed necessary, and elimination of unnecessary preoperative standing “screening tests,” limiting investigations to only appropriate ones
7.
Optimization of the patient’s physiologic condition
8.
Stratification of patient risk regarding morbidity and mortality
9.
Formulation of an anesthetic plan and organization of resources for perioperative care and postoperative recovery
10.
Documentation of informed consent for anesthesia and planned surgical procedure

The preanesthetic evaluation may be performed well in advance of the planned operation for most elective procedures during a visit to the preanesthetic evaluation clinic. It may be performed on the bedside in the hospital ward or intensive care unit on the “night before” for inpatients. For urgent and emergent procedures, a brief, focused preanesthetic evaluation is performed just before surgery. The consensus of the ASA Task Force is that an initial record review, patient interview, and physical examination should be performed prior to the day of surgery for patients with high severity of disease and those undergoing procedures with high surgical invasiveness.

Preanesthesia clinics have been shown to improve operating room efficiency and minimize unexpected delays and cancellations due to poorly prepared patients. ^, In one study the preoperative evaluation led to a change in the proposed anesthetic plan in up to 15% of healthy individuals and 20% of ill patients. In a study from Stanford University, implementation of the preanesthetic clinic evaluation produced an 87.9% reduction in day-of-surgery cancellations. It is estimated that $30 to $40 billion is spent annually on preoperative testing and subsequent follow-up in North America alone, of which 50% could be saved by the appropriate and selective ordering of tests. In one study the implementation of a preoperative clinic, where the ordering of tests was at the anesthesiologist’s request, resulted in a savings of $112.09 per patient. This is equated with an annual potential saving of over $1.01 million at one institution. Briefly, the preanesthesia evaluation is critical to ensure patient safety, good surgical outcomes, patient satisfaction, and reduction of health care costs.

The advent of the ERAS program has further cemented the value of preanesthesia evaluation. ERAS programs involve an interdisciplinary, multimodal approach to evidence-based standardized perioperative care, integrating preoperative, intraoperative, and postoperative periods to achieve early recovery for patients undergoing any major surgery. Implementation of ERAS pathways for spine surgery has been shown to decrease postoperative intensive care unit admissions, length of hospital stay, complications, readmissions, and blood loss, in addition to improving pain control with decreased opioid consumption, improving mobilization and ambulation, and reducing health care costs. Likewise, implementation of an ERAS program has been associated with a significant reduction in the postoperative hospital stay and accelerated recovery without increasing complication rates following elective craniotomy. Preanesthesia evaluation and counseling is fundamental to ERAS by providing timely information to patients to optimize physical and psychological function, reduce anxiety, and prepare them to meet the ERAS milestones. Typical preanesthesia goals for ERAS include patient education and counseling, risk assessment screening and intervention, carbohydrate and protein loading, shortened preoperative fasting, and implementation of the analgesia regimen. Other preoperative interventions include orientation to pain management approach, prehabilitation to promote muscle strength, surgical site management, vitamin D regulation for healing, optimization of comorbid conditions, and smoking cessation. Irrespective of the institution-specific emphasis on select components of the ERAS pathway, incorporation of preanesthesia clinics is critical to the success of enhanced recovery programs.

Same-day neurosurgery (outpatient or ambulatory neurosurgery), in which patients are discharged from the hospital on the same calendar day (hospital admission <24 hours), is increasingly common in many centers. Hospital-based outpatient lumbar decompression increased from 18.7% to 68.5% in the United States between 2003 and 2014. In addition, with the successful demonstration of safety, feasibility, and cost benefits in select centers, there is growing interest in same-day discharge for anterior spinal discectomy and fusion as well as intracranial surgery. Although careful selection of patients appropriate for outpatient surgery begins in the surgeon’s clinic, all patients scheduled for outpatient neurosurgical procedures should be screened preoperatively by a neuroanesthesiologist well in advance to avoid complications and unplanned conversions to inpatient status on the day of surgery. Morbid obesity is often considered a risk factor for unplanned admission and increased perioperative complications, including infection. In general, patients with a body mass index (BMI) >50 kg/m ² are considered to have an unacceptable level of risk for ambulatory surgery. Other anesthetic considerations for ambulatory surgery include anticipated difficult airway and/or bag-mask ventilation, significant cardiovascular disease, pulmonary insufficiency, obstructive sleep apnea, and abnormal sensitivity to anesthetic medications. Uncontrolled seizures, poor preoperative neurological status or decreased cognitive function, and psychological instability also preclude ambulatory surgery. Last but not the least, the patient’s social situation including presence of a reliable caregiver is essential to safely discharge early after surgery.

General Preanesthetic Evaluation

During the preanesthesia evaluation, the effects of anesthesia, positioning, surgery, and postoperative pain must be considered in relation to the patients’ surgical state and medications. The patient’s preexisting medical condition, unrelated to the proposed surgical procedure, may require more intense scrutiny than the pathologic process being treated. The ASA classification of physical status is a universally accepted system used for stratification of the patient’s preexisting health status ( Table 7.1 ). Although it does not take into account the surgical risk, and is not primarily designed for outcome prediction, it correlates with perioperative morbidity and mortality. In fact, ASA physical status of 3 to 5 independently predicts perioperative cardiovascular complications in intracranial surgical patients, and is also a risk factor for perioperative mortality.

TABLE 7.1

American Society of Anesthesiologists (ASA) Classification of Physical Status

Excerpted from the Relative Value Guide 2016 of the American Society of Anesthesiologists. A copy of the full text can be obtained from ASA, 1061 American Lane, Schaumburg, IL 60173-4973 or online at www.asahq.org .

ASA Physical Status	Disease State
1	A normal healthy patient
2	A patient with mild systemic disease
3	A patient with severe systemic disease
4	A patient with severe systemic disease that is a constant threat to life
5	A moribund patient who is not expected to survive without the operation
6	A declared brain-dead patient whose organs are being removed for donor purposes

Specific neurosurgical aspects of preanesthesia evaluation are discussed separately later in this chapter. The general approach is summarized here.

Medical History

1.
Medical history related to intended surgical procedure and other constitutional diseases
2.
History of previous surgery and anesthesia (insight into problems with airway management, intravenous access, postoperative pain and nausea and vomiting, and so on)
3.
Current medications (anticonvulsant therapy is associated with increased resistance to nondepolarizing muscle relaxants and hence increased requirement; steroid administration might be associated with hyperglycemia and adrenal suppression) and allergies (e.g., allergy to latex, antibiotics, adhesive tape)
4.
Personal history (smoking, alcohol, recreational drug use—all of which have bearing on anesthesia and intraoperative care)
5.
Relevant family medical history and social and religious background (e.g., Jehovah’s Witnesses)

American Society of Anesthesiologists Perioperative Brain Health Initiative and Cognitive Assessment of Geriatric Patients

Approximately one-third of the surgical procedures performed in the United States are performed on patients ≥65 years of age. In addition to a reduced physiologic reserve, older surgical patents have an increased burden of comorbid conditions and have a higher rate of perioperative complications and poor surgical outcomes. ^, Postoperative neurocognitive disorders, ranging from transient delirium and delayed neurocognitive recovery to postoperative neurocognitive disorder, are among the most significant postoperative neurological complications for older patients. In 2015 the ASA launched the Perioperative Brain Health Initiative, a patient safety initiative to minimize the impact of preexisting cognitive deficits and optimize the cognitive recovery and perioperative experience for adults aged ≥65 years ( https://www.asahq.org/brainhealthinitiative/about ).

The standard preoperative evaluation in geriatric patients should be supplemented with a review of geriatric syndromes such as frailty, cognitive impairment, and dementia in addition to assessment of functional capacity. Although a basic geriatric assessment may be performed in the preanesthesia clinic, select patients may benefit from a more comprehensive assessment by a geriatric specialist. As many as 24% to 60% of geriatric age-group patients scheduled for elective surgery may have previously undiagnosed cognitive impairment preoperatively, and such impairment is associated with development of postoperative delirium, longer hospital stay, and lower likelihood of going home at hospital discharge. ^, Although the prevalence of cognitive impairment in geriatric patients presenting for intracranial surgery is unknown and postoperative neurocognitive recovery may be affected by intracranial surgery itself, screening for cognitive impairment should be a routine part of the preoperative assessment in patients >65 years of age. This may be particularly relevant in older patients presenting for complex spinal fusion surgery. The American Geriatrics Society guidelines recommend performing a preoperative assessment of delirium risk factors, including the following five major risk factors: age >65 years, chronic cognitive decline or dementia, poor vision or hearing, severe illness, and presence of infection. Despite a number of studies showing that preoperative cognitive function is a consistent predictor of postoperative cognitive dysfunction, cognitive screening of older adults as a part of preanesthetic evaluation is still not routine. The American College of Surgeons (ACS) National Surgical Quality Improvement Program (NSQIP) and the American Geriatrics Society Best Practices Guidelines recommend assessing cognitive ability in any patient older than 65 years to assess the risk of postoperative cognitive dysfunction.

Some options for preoperative cognitive screening tools include the animal fluency test, the Montreal Cognitive Assessment, and the Mini-Cog. ^, These are quick and acceptable to patients in the preoperative setting. ^, The Mini-Cog, in particular, is increasingly used ( https://mini-cog.com ). It involves a three-item recall test for memory and a clock-drawing test. The cutoff varies; in general, scores equal to or less than 2 are consistent with some impairment. Preoperative cognitive testing identifies vulnerable geriatric patients who may benefit from further testing or counseling during their preoperative evaluation in addition to recommendations for perioperative care to institute interventions likely to reduce the risk of delirium or cognitive decline.

General Physical Examination

The general physical examination should account for the patient’s level of consciousness, mental status, build, nutrition, and vital parameters. Patients with malignant tumors and those with high cervical lesions might be emaciated with significantly reduced muscle mass. On the other hand, obesity might be coexisting in many patients. Obese individuals have increased likelihood of associated diabetes, hypertension, coronary artery disease (CAD), restrictive lung disease, sleep apnea, and gastroesophageal reflux, which might warrant alteration in the anesthetic plan. Difficulty in tracheal intubation may be encountered more frequently in obese compared with lean individuals, and the pharmacologic profile of anesthetic agents may also be altered. Some neurosurgical patients might be dehydrated owing to reduced intake of fluids (because of impaired consciousness) or vomiting, or because of the use of diuretics and contrast agents. Correction of dehydration before induction of anesthesia can prevent postinduction hypotension. Significant blood loss is a possibility in surgery for intracranial aneurysms, arteriovenous malformations (AVMs), vascular tumors, craniosynostoses, and extensive spine surgeries. Preanesthetic evaluation should look for preexisting anemia and correct it preoperatively or arrange for intraoperative transfusion on a case-by-case basis. Recording of preoperative vital parameters (heart rate, blood pressure) provides baseline values for intraoperative management.

A crucial aspect of general examination is assessment of the patient’s airway. Routine maneuvers used for airway management may worsen spinal instability in patients with cervical lesions and may lead to increased intracranial pressure (ICP) with potentially devastating consequences in patients with decreased intracranial compliance. Mallampati scoring, thyromental distance, presence of overbite or underbite, and neck flexion and extension collectively provide an estimate of the risk of difficult intubation. Some specific situations in which difficult airway should be anticipated include patients with recent supratentorial craniotomy in whom the mouth opening might be significantly reduced secondary to temporalis muscle contracture, or ankylosis of the temporomandibular joint, acromegalic patients undergoing pituitary surgery, and cervical spine lesions. Recognition of potential airway difficulty allows proper planning with accessory equipment and resources, as well as formulation of backup plan.

Assessment of System Functions

Frailty Assessment

Frailty is defined as a decrement in physiologic reserves that can affect the resilience of a patient to recover from illness or disease independent of age. The concept of frailty has been well recognized in geriatric practice for a long time but has gained increased attention in the context of surgery and anesthesia in the last few years. Frailty is now recognized to be associated with increased vulnerability to stress such as surgery and anesthesia and with higher risk of postoperative complications, and poor surgical outcomes and recovery after a variety of surgical procedures. In fact, frailty scores may better predict postoperative outcomes in older individuals than ASA physical status and may be valuable for preoperative risk stratification. Specific to the neurosurgical population, frailty has been shown to be associated with higher mortality and prolonged hospital stay after resection of spine tumors and poor outcome (modified Rankin Scale scores 3–6) after subarachnoid hemorrhage (SAH). ^, Preoperative frailty in patients undergoing brain tumor resection is associated with an increased risk of postoperative complications (including pneumonia, urinary tract infection, deep vein thrombosis, pulmonary embolism, new neurological deficit, cerebrospinal fluid leak, and wound dehiscence or infection), longer length of hospital stay, and discharge to a location other than home. Consequently, assessment of frailty as a part of preanesthesia evaluation is increasingly being recognized as critical for older neurosurgical patients. Preoperatively frail patients may benefit from individualized multidisciplinary consultations such as a comprehensive geriatric assessment, discussions regarding prognosis and risk, and consideration for prehabilitation. It has been shown that a multifaceted interdisciplinary treatment program targeting specific elements of frailty can improve frailty and increase mobility. Specifically, dietitian-evaluated nutritional intake and nutritional supplements for underweight patients, psychiatrist or psychologist consultation and encouragement for greater social engagement in patients with depression or those meeting exhaustion criteria, and physiotherapy sessions and home exercise program in patients who met the weakness, slowness, or low energy expenditure criteria were effective in improving frailty. Although similar studies in the neurosurgical population are lacking, awareness of frailty may be helpful in tailoring preoperative counseling and rehabilitation. At a minimum, frailty assessment can be used to alert surgeons to the risks and lead to closer postoperative monitoring with attention to hydration, nutrition, and mobilization.

There are several approaches to frailty evaluation. Simplistically, most scales depend either on identification of a phenotype including certain physical traits (the frailty phenotype, or Fried Index), or the assessment of deficiencies across several domains. The Fried phenotype is relatively simple and consists of five criteria: weight loss, weak hand-grip strength, exhaustion, slow gait, and low physical activity. Scores of 4 to 5 are considered frail, 2 to 3 intermediately frail, and 0 to 1 not frail. The Hopkins frailty score (HFS) includes five components: shrinking, weakness, exhaustion, low activity, and slowed walking speed, with each domain yielding a dichotomous score of 0 or 1 based on specific criteria. The cumulative score then classifies the patients as frail (HFS 4–5), moderately frail (HFS 2–3), or nonfrail (HFS 0–1). Widespread implementation of frailty assessment is currently not within the capacity of majority of preanesthesia clinics. Nevertheless, given its growing significance, it is imperative that the preanesthesia evaluation incorporate capacity for frailty assessment with support for geriatric consultations.

Neurological System

Patients with a depressed level of consciousness preoperatively are likely to have reduced anesthetic need for induction, are more likely to have a slow or delayed emergence postoperatively, and may need postoperative mechanical ventilation. Such patients should not receive any sedative or narcotic agent unless they are under continuous supervision, with vigilance for respiratory depression. Patients who had previous motor deficits may develop exacerbation of focal neurological signs after sedative doses of benzodiazepines and narcotics. Presence of brainstem lesions and/or lower cranial nerve dysfunction predisposes patients to an increased risk of aspiration postoperatively. Finally, patients with major preexisting motor deficits may develop a life-threatening hyperkalemia secondary to succinylcholine administration. Succinylcholine has also been reported to cause hyperkalemia in patients with ruptured cerebral aneurysms independent of the presence of motor nerve disturbances, although this appears to be uncommon. Elevated ICP often presents with headache with nausea and vomiting, but can also lead to olfactory nerve dysfunction with loss of sense of smell, or sixth nerve palsy. Unilateral uncal herniation would result in a dilated unresponsive ipsilateral pupil, which should be distinguished from incidental anisocoria, or a unilateral third nerve palsy resulting from compression by a space-occupying lesion. Limitations of the field of vision in patients with pituitary and other suprasellar tumors should be documented for postoperative comparison. Dysfunction of the trigeminal nerve and facial nerve may interfere with mask ventilation and tracheal intubation. A patient with a damaged vagus nerve may present with a hoarse voice secondary to vocal cord paralysis and may be at increased risk of airway obstruction.

Respiratory System

The risk of perioperative respiratory complications is increased in the presence of preexisting obstructive or restrictive pulmonary disease. Perioperative hypoxemia or hypercapnia is more likely to occur and can aggravate an already compromised cardiorespiratory status. Patients with associated pulmonary disease require an assessment of their baseline status, and any element of potential reversibility should be addressed. Smoking is a common important risk factor for both cardiovascular and pulmonary disease and is associated with a threefold increase in perioperative morbidity. Cessation of smoking for 6 to 8 weeks is recommended for reactivation of mucociliary clearance, but cessation for as little as 24 hours can reduce the carboxyhemoglobin levels and improve oxygenation. The presence of reactive airway disease indicates an increased risk of bronchospasm with airway manipulation and tracheal extubation, and an increased risk of coughing and laryngospasm during emergence. In patients with symptomatic obstructive pulmonary disease, preoperative pulmonary function testing before and after bronchodilators allows assessment of reversibility and determination of optimal preparation. Some patients with sleep apnea might be using continuous positive airway pressure (CPAP) devices at home, and it is important to ensure that the same device is available postoperatively.

Patients with decreased levels of consciousness due to intracranial pathology and those with a high spine lesion or lower cranial nerve paralysis might have atelectasis preoperatively, which puts them at increased risk of postoperative mechanical ventilation. Aspiration pneumonitis and/or superimposed pneumonia can also occur. A restrictive pattern of lung disease often occurs in patients with craniovertebral junction anomalies preoperatively, which persists in the postoperative period. The following patient-related risk factors predict postoperative pulmonary complications: advanced age, ASA class II or greater, functional dependence, chronic obstructive pulmonary disease (COPD), and congestive heart failure. Other factors indicating increased risk include impaired sensorium, abnormal findings on chest examination, cigarette use, alcohol use, and weight loss. Although asthma is not a risk factor if well controlled, the perioperative risk may be increased if it is poorly controlled. Important procedure-related risk factors include neurosurgery, emergency surgery, and prolonged surgery. The value of preoperative testing to estimate pulmonary risk is controversial. Although an abnormal chest radiograph does indicate an increased risk for postoperative pulmonary complications and spirometry may provide some risk stratification, among potential laboratory tests to stratify risk, a serum albumin level less than 35 g/L is the most powerful predictor.

Cardiovascular System

The presence of cardiovascular disease significantly increases anesthesia risk, and optimizing the patient’s condition can significantly improve outcome. Major adverse cardiac events (MACEs) after noncardiac surgical procedures are often associated with prior CAD. The stability and timing of a recent myocardial infarction (MI) affect the incidence of perioperative morbidity and mortality. Postoperative MI and 30-day mortality decrease substantially as the length of time from MI to operation increases. Most data indicate that ≥60 days should elapse after an MI before noncardiac surgical procedures in the absence of a coronary intervention. In chronic hypertension, increased cerebrovascular resistance causes the lower and upper limits of cerebral blood flow (CBF) autoregulation to shift to higher pressure levels, and consequently poor tolerance to acute hypotension. ^, However, adaptive hypertensive changes in CBF autoregulation may be reversible with adequate control of blood pressure. ^, Left ventricular dysfunction with symptoms of cardiac failure indicates significantly reduced cardiac output, which can worsen with general anesthesia. In fact, patients with heart failure may have a higher 30-day postoperative mortality rate than those with atrial fibrillation or CAD. Mannitol must be used judiciously or not at all in the presence of left ventricular failure. Beta blockers should be continued in patients who have been on them chronically. ^, Particular attention should be paid to the need to modify or temporarily discontinue beta blockers as clinical circumstances (e.g., hypotension, bradycardia, bleeding) dictate. ^, In patients with intermediate or high-risk MI noted in preoperative risk stratification tests, it may be reasonable to begin perioperative beta blockers. However, beta-blocker therapy should not be started on the day of surgery. According to the Revised Cardiac Risk Index (RCRI), the presence of three or more of the following factors is associated with cardiac morbidity of 11%: (1) high-risk surgery, (2) history of ischemic heart disease, (3) history of congestive heart failure, (4) history of cerebrovascular disease, (5) preoperative treatment with insulin, and (6) preoperative serum creatinine level greater than 2.0 mg/dL.

Preoperative cardiac evaluation must be carefully tailored to the circumstances and nature of the surgical illness. The 2014 update of the American College of Cardiology (ACC)/American Heart Association (AHA) guidelines on perioperative cardiovascular evaluation and care for noncardiac surgical procedures defines urgency of surgery in the context of perioperative risk. An emergency procedure is one in which life or limb is threatened if not in the operating room and there is limited time for clinical evaluation, typically <6 hours. For an urgent procedure, 6 to 24 hours may be available for a limited clinical evaluation. A time-sensitive procedure is one in which a delay of >1 to 6 weeks to allow for an evaluation and significant changes in management will negatively affect outcome. An elective procedure is one that could be delayed for up to 1 year. A low-risk procedure is one in which the combined surgical and patient characteristics predict a risk of a MACE of death or MI of <1%. Procedures with a risk of MACE of ≥1% are considered to have an elevated risk. The ACS prospectively collected data on operations performed in more than 525 participating hospitals in the United States, and data on more than 1 million operations have been used to create surgical risk calculators ( www.riskcalculator.facs.org ). Anesthesia and surgery are increasingly becoming safer, and this affects the subjective “readiness” of a patient with cardiac disease for neurosurgery. For instance, the cardiac risk in patients with significant aortic stenosis who are undergoing noncardiac surgical procedures has substantially declined. Consequently, according to the current recommendations, elevated-risk elective noncardiac surgical procedures with appropriate intraoperative and postoperative hemodynamic monitoring are reasonable to perform in patients with asymptomatic severe aortic stenosis.

Functional status is a reliable predictor of perioperative and long-term cardiac events. Patients with reduced functional status preoperatively are at increased risk of complications. Conversely, those with good functional status preoperatively are at lower risk. In highly functional asymptomatic patients, it is often appropriate to proceed with planned surgery without further cardiovascular testing. Functional status can be estimated from activities of daily living, often expressed in terms of metabolic equivalents (METs). Perioperative cardiac and long-term risks are increased in patients unable to perform 4 METs of work during daily activities. Examples of activities associated with >4 METs are climbing a flight of stairs or walking up a hill, walking on level ground at 4 mph, and performing heavy work around the house. In an acute surgical emergency, preoperative evaluation might have to be limited to simple and critical tests such as rapid clinical assessment, hematocrit, electrolytes, renal function, and ECG, with a more extensive evaluation conducted after surgery. In patients in whom coronary revascularization is not an option, it is often not necessary to perform a noninvasive stress test. In general, preoperative tests are recommended only if the information obtained will result in a change in the surgical procedure performed, a change in medical therapy or monitoring during or after surgery, or a postponement of the operation until the cardiac condition can be corrected or stabilized. A cardiologist consultation should be sought only if deemed necessary and if surgical circumstances allow.

The 2014 ACC/AHA guidelines recommend an algorithmic approach to perioperative cardiac assessment on the basis of the available evidence and expert opinion. This approach may be conveniently described in the following steps:

Step 1: In patients scheduled for surgery with risk factors for or known CAD, the urgency of surgery should be determined. If an emergency, surgery should proceed with appropriate monitoring and management strategies.
Step 2: If the operation is urgent or elective, determine if the patient has an acute coronary syndrome. If yes, then the patient should be referred for cardiologic evaluation and management.
Step 3: If the patient has risk factors for stable CAD, then the perioperative risk of a MACE is estimated on the basis of the combined clinical/surgical risk using the risk calculator ( http://www.surgicalriskcalculator.com ) or incorporating the RCRI.
Step 4: If the patient has <1% risk of a MACE, the operation may proceed without further testing.
Step 5: If the patient is at elevated risk of a MACE, then functional capacity is determined. If the functional capacity is ≥4 METs, then the operation can proceed without further evaluation.
Step 6: If the patient has <4 METs or unknown functional capacity, then the need for further testing depends on the possibility that the test results will affect patient decision making (e.g., decision to perform original operation or willingness to undergo cardiac intervention, depending on the results of the test). In patients with unknown functional capacity, exercise stress testing may be reasonable to perform. If the stress test result is abnormal, cardiac intervention may have to be considered prior to the planned operation or alternative noninvasive treatment of the indication for surgery (e.g., radiation therapy). If the test is normal, the operation should proceed.
Step 7: If testing is unlikely to affect decision making, the operation should proceed or an alternative noninvasive treatment of the indication for surgery may be considered.

The guidelines also recommend that elective noncardiac operations be delayed for 14 days after balloon angioplasty, 30 days after bare metal stent implantation, and 365 days after drug-eluting stent implantation (but may be considered after 180 days of implantation of a drug-eluting stent if the risk of further delay is greater than the expected risks of ischemia and stent thrombosis). In patients undergoing an urgent noncardiac operation during the first 4 to 6 weeks after bare metal or drug-eluting stent implantation, dual antiplatelet therapy should be continued unless the relative risk of bleeding outweighs the benefit of the prevention of stent thrombosis. In patients undergoing surgical procedures that mandate the discontinuation of platelet receptor–inhibitor therapy, it is recommended that aspirin be continued if possible. In patients undergoing a nonemergency/nonurgent noncardiac surgical procedure who have not had previous coronary stenting, it may be reasonable to continue aspirin when the risk of potential increased cardiac events outweighs the risk of increased bleeding.

Gastrointestinal System

Patients at risk of aspiration include those with full stomachs, bowel obstruction, or gastroesophageal reflux. Patients with dysfunction involving the 9th and the 10th cranial nerves, as well as those with a decreased level of consciousness, are also at risk if they have not been fasting. In these patients, general anesthesia may be induced using a rapid sequence with cricoid pressure to minimize the risk of aspiration.

Renal System

Patients presenting for neurosurgical intervention sometimes have coexistent acute or chronic renal dysfunction. Patients with renal disease present an anesthetic challenge, as they may have autonomic neuropathy, encephalopathy, fluid retention (congestive heart failure, pleural effusion, ascites) despite intravascular volume depletion, hypertension, metabolic acidosis, electrolyte imbalances (hyperkalemia, hyponatremia, hypocalcemia), anemia, and delayed gastric emptying. The generalized effects of azotemia mandate a thorough evaluation of patients in renal failure. Signs of fluid overload or hypovolemia should be sought. Hematocrit, serum electrolytes, coagulation studies, blood urea nitrogen (BUN), and creatinine measurements are advisable. A chest radiograph and arterial blood gas analysis might be required in patients with breathlessness, and the ECG should be examined for signs of hyperkalemia or hypocalcemia, as well as ischemia and conduction blocks. Severely anemic patients may require preoperative red blood cell transfusions. Preoperative drug therapy should be carefully reviewed for drugs with significant renal elimination. Dosage adjustments and measurements of blood levels are sometimes necessary to prevent drug toxicity.

Intravascular volume depletion, contrast dye injections, aminoglycoside antibiotics, angiotensin-converting enzyme inhibitors, and nonsteroidal antiinflammatory drugs (NSAIDs) are risk factors for an acute deterioration in renal function and should be minimized. Hypovolemia appears to be a particularly important factor in the development of acute postoperative renal failure. The emphasis in management of these patients is on prevention because of the high mortality associated with postoperative renal failure. Optimal management may require preoperative dialysis in select situations, the usual indications being severe acidosis or volume overload, hyperkalemia, metabolic encephalopathy, and drug toxicity. Neuromuscular blocking agents not dependent on renal function for their elimination should be selected. Mannitol is contraindicated in anuric patients. Postoperative mechanical ventilation is sometimes required in patients with renal failure, because inadequate spontaneous ventilation with progressive hypercapnia can result in respiratory acidosis that may exacerbate preexisting acidosis, lead to potentially severe circulatory depression, and dangerously increase serum potassium concentration.

Hematologic System

Intracranial hemorrhage is a potentially lethal catastrophe. Therefore any bleeding tendency should be investigated thoroughly and corrected preoperatively. If deemed necessary, appropriate clotting factors and platelets should be made available at the time of surgery. Patients on NSAIDs such as aspirin should have their medications stopped for a week before intracranial surgery. This decision may have to be modified in patients with transient ischemic attacks, when the risk of discontinuation may exceed those of the benefits.

The use of direct oral anticoagulants (DOACs) is increasing prevalent. They are commonly used for the prevention and treatment of venous thromboembolism and for the prevention of cerebrovascular embolism in patients with nonvalvular atrial fibrillation. DOACs selectively inhibit the enzymatic activity of thrombin and factor Xa, leading to a rapid and predictable anticoagulant effect. Dabigatran competitively inhibits thrombin in a concentration-dependent manner, inhibits tissue factor–induced thrombin generation, and decreases endogenous thrombin generation. Apixaban, rivaroxaban, and edoxaban inhibit free and bound factor Xa to reduce thrombin generation. Elderly patients presenting for neurosurgical procedures are often likely to be on oral anticoagulants, including DOACs. Given the catastrophic implications of postoperative bleeding in neurosurgery, perioperative management of anticoagulation therapy is critical. Preoperative interruption of DOACs is required for practically all neurosurgical procedures. However, the preanesthesia evaluation should address the optimal timing of such interruption, potential need for bridging therapy, and timing for restarting anticoagulation.

Anticoagulant half-life is agent specific and is significantly influenced by renal function; dabigatran is affected to a greater extent by renal impairment than the direct factor Xa inhibitors. In general, all guidelines recommend withholding factor Xa inhibitors preoperatively for at least 48 hours, irrespective of renal function. The French Working Group recommends holding off for 72 hours, regardless of renal function, whereas the ACC suggests 72 hours if the creatinine clearance is <30 mL/min. ^, All guidelines recommend stopping dabigatran at least 96 hours prior to elective surgery if the creatinine clearance is <50 mL/min, except the French Working Group, which recommends 120 hours of cessation.

Bridging of anticoagulation is another important consideration to minimize the risk of thrombosis. However, evidence demonstrates that in patients with atrial fibrillation requiring DOAC therapy interruption for elective surgery or procedures, perioperative management without heparin bridging or coagulation function testing was safe and associated with low rates of major bleeding and arterial thromboembolism. Likewise, forgoing bridging therapy in patients with atrial fibrillation on vitamin K antagonists has been shown to be noninferior to bridging. Heparin bridging is currently recommended only for patients with a CHA ₂ DS ₂ -VASc score ≥7 or a CHADS ₂ score ≥5. The CHA ₂ DS ₂ -VASc score (congestive heart failure [+1], hypertension [+1], age ≥75 years [+2], diabetes [+1], previous stroke, transient ischemic attack, or thromboembolism [+2], vascular disease [+1], age 65–74 years [+1], female sex [+1]) estimates the risk for thromboembolism in patients with atrial fibrillation. Because of the short onset and offset of effect, bridging therapy is not usually recommended with DOACs. For emergent procedures, patients on dabigatran can be reversed with the monoclonal antibody idarucizumab. For patients on apixaban and rivaroxaban, an antidote, andexanet, is available, but its cost is prohibitive. Alternatively, four-factor prothrombin concentrate complex and factor eight inhibitor bypass activity (FEIBA) have been used with apparent efficacy.

Although anticoagulant medications have to be typically stopped prior to open neurosurgery, the consideration for endovascular neurosurgery is somewhat opposite. Thromboembolic events represent a clinically significant cause of neurological morbidity during endovascular management, particularly of cerebral aneurysms. Consequently patients are often electively started on antiplatelet agents preoperatively. There appears to be no uniform strategy for preoperative and postoperative anticoagulation for endovascular interventions, but it is common for patients to be placed on an antithromboembolic regimen of 81 mg of aspirin and 75 mg of clopidogrel daily, starting 7 days prior to elective aneurysm coiling. Alternatively the patient receives a loading dose of 300 mg of clopidogrel prior to the procedure, and then is started on a maintenance dose of aspirin and clopidogrel.

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