Anesthesiology

Awake Craniotomy

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What the Anesthesiologist Should Know before the Operative Procedure

"Awake" craniotomy is a bit of a misnomer. Most of these procedures are done using an "asleep-awake-asleep" technique. During line and block placement, pinning, craniotomy, and bone flap, the patient is asleep, using a variety of airways (natural, nasal trumpet, laryngeal mask airway [LMA], endotracheal). The patient is then awakened for continuous neuromonitoring as the lesion is mapped and then excised. This "awake" portion is what makes the technique unique and different from the standard asleep craniotomy. The patient has to be cooperative enough to interact with the monitoring team while tolerating the stress of surgery, positioning, and airway manipulation. After the lesion has been excised, the patient is usually returned to sleep for closure of the craniotomy.

Patients undergoing awake craniotomies usually have a pathologic lesion (tumor, epileptic focus) in the eloquent part of the brain (Wernicke's, Broca's) or critical dexterity portion of their motor homunculus. Alternatively, awake craniotomies are performed for deep brain stimulator placement and the patient must be responsive to the surgeon. Due to coordination of services (neurosurgery, anesthesia, neuromonitoring), the procedure is rarely, if ever, an emergency. Therefore, patient must be medically optimized before undergoing the procedure.

The unique conditions of an awake (versus asleep) self-selects the patient population capable of tolerating the procedure. Patients have to be mentally competent and relatively healthy and be willing to undergo the lines, blocks, and manipulation of the airway that may be stressful to endure while awake. Patients with known difficult airways, sleep apnea, anxiety disorder, claustrophobia, alcohol or substance abuse, lower back pain, or morbid obesity should be heavily scrutinized.

1. What is the urgency of the surgery?

What is the risk of delay in order to obtain additional preoperative information?

Due to the complexity of awake craniotomies, the procedure is rarely emergent. The pathologies associated with this procedure are usually diagnosed incidentally (change in speech, dexterity, seizure) or with no symptoms (CT scan after a trauma). It is rare for tumors in this area to be fast growing, and if there is a life-threatening lesion, the procedure is often done asleep emergently.

Emergent: These procedures are almost never done emergently. If the pathology or symptoms are emergent, the craniotomy should be done asleep. Intraoperative neuromonitoring (SSEP, MEP) can help reduce the risk of postoperative neurologic deficits.

Urgent: If the patient is medically optimized and the appropriate personnel and equipment are available, then the procedure can be facilitated more urgently.

Elective: The majority of awake craniotomies are done electively. The patient is diagnosed, and the decision is made by a neurosurgeon to proceed awake. Both anesthesia and neurology are consulted, and the procedure is scheduled when the appropriate resources are available.

2. Preoperative evaluation

First the patient needs to be evaluated for neurologic deficits. Changes in speech and/or motor function, new-onset seizures, or incidental radiologic findings will lead to further workup including neurologic testing, head CT, and MRI. Functional MRI evaluates speech and motor function with brain activity near the lesion. If the lesion is appropriate for an awake approach, the patient requires further work up. The patient has to be mentally competent, able to follow commands, and able to lie flat for several hours. The patient has to be able to protect his or her airway and tolerate sedation without significant obstruction, hypercarbia, or hypoxemia. Patients with anxiety disorder, claustrophobia, and/or alcohol or substance abuse must be counseled on the length and possible stressors of the procedure.

Medically unstable conditions warranting further evaluation include unstable angina, arrhythmias, asthma, seizures, fever/infection, hypo/hyperglycemia, acute renal failure, and acute pain. Delaying surgery may be indicated until these conditions are sufficiently medically optimized, if the patient is considered to have a full stomach, or if the appropriate personnel (anesthesia and neuromonitoring) are not available.

3. What are the implications of co-existing disease on perioperative care?

The patient's coexisting diseases have to be optimized so that the patient can tolerate the stress of the surgery and the unique anesthetic considerations for the awake portion of the surgery. Although the plane of anesthesia is "lighter" than a general anesthesia for a standard asleep craniotomy, there are risks of intraoperative complications that differ from those for patients with a controlled airway. The "awake" patient is at a significant risk of obstruction, hypoxemia, seizure, and aspiration. Also, the procedure shares similar risks to the standard asleep approach such as cerebral and myocardial ischemia, intracranial hypertension, and stroke.

Perioperative evaluation

In addition to the neurologic workup for the awake craniotomy, other comorbidities should be appropriately evaluated and optimized (see each system below).

Perioperative risk reduction strategies

Patients should continue taking their beta-blocker, anticonvulsant, antacid (H2 blockers, proton pump inhibitors [PPIs]), anxiolytic, antidepressant (with the exception of monoamine oxidase inhibitors [MAOIs]), and asthma/chronic obstructive pulmonary disease (COPD) medications up to the day of surgery. Antiplatelet therapy and warfarin should be discontinued 7 days before surgery. Other medications should be taken up to the day before therapy and held in the morning.

b. Cardiovascular system

Acute/unstable conditions

Coronary artery disease, unstable angina, arrhythmias, cardiomyopathy, congestive heart failure, valvular diseases, and carotid artery disease should be evaluated with the goal of determining the patient's functional status.

Baseline coronary artery disease or cardiac dysfunction: goals of management

The patient's ability to tolerate the awake craniotomy needs to be balanced with possible intervention. Patients with unstable angina or active myocardial ischemia need to be revascularized. Arrhythmias should be stable and rate controlled or paced (including automated internal cardioverter/defibrillator [AICD] placement). The extent of carotid stenosis is especially important to measure and possibly treat due to the changes in cerebral blood flow that can occur during the awake craniotomy and the need for collateral circulation. The extent of valvular disease will determine the extent of intraoperative invasive monitoring needed.

c. Pulmonary

COPD

Most patients undergoing awake craniotomy should not have significant COPD. The patient needs to be able to tolerate mild sedation with minimal oxygen therapy and the possibility of general anesthesia. Patients with controlled COPD should optimize their medication regimen, including steroids if necessary.

Reactive airway disease (asthma)

Patients with brittle reactive airway disease are not candidates for awake craniotomies due to the lack of a controlled airway and the preference for total intravenous anesthesia (TIVA) versus inhaled anesthesia (and avoidance of ketamine for sedation). Patients with mild, controlled asthma should maintain their medication regimen, including steroids if necessary.

d. Renal-GI:

Renal

Patients with end-stage renal disease (ESRD) should be dialyzed the day before or day of surgery. Electrolytes and fluid status should be under tight control.

GI

Due to the risk of aspiration, patients with uncontrolled gastroesophageal reflux disease (GERD) are not candidates for awake craniotomy. Those with well-controlled GERD should continue to take their H2 blockers or PPIs on the day of surgery. If necessary, a nonparticulate antacid can be given the day of surgery. Diabetics and patients with gastroparesis should be given metoclopramide the day of surgery. Patients should be NPO for at least 6 hours.

e. Neurologic:

A majority of patients undergoing awake craniotomy will have concomitant neurologic disease associated with the lesion: usually speech or cognitive dysfunction, motor weakness, vision changes, headache, or seizures. Patients may also have other neurologic disease not related to the primary lesion that may factor in their management during awake craniotomy.

Acute issues

Active seizures need to be under control before undergoing surgery, and surgery should be delayed until the postictal phase has passed and the patient is lucid. Patients with prodromal, ongoing, or postdromal migraines will poorly tolerate the procedure, so they should be symptom free before proceeding.

Chronic disease

During the procedure, the brain will be directly stimulated with electricity, so patients with seizure disorder need to be under tight control before undergoing awake craniotomy. The appropriate anticonvulsant regimen should be established and dosed up to the procedure itself. Patients on heavily sedating anticonvulsants (benzodiazepines, barbiturates) may not be good candidates for awake procedures. The need for continuous intraoperative neurologic testing necessitates that the patient be cooperative and communicative. Patients with intellectual disability, significant cognitive impairment, or psychosis are poor candidates. Anxiety disorder and claustrophobia can also prove problematic if the patient is not able to tolerate the blocks, lines, and positioning (often including Mayfield pinning) associated with the hours-long procedure. Patients with alcohol or substance abuse may be difficult to sedate, and the therapeutic window of sedatives and opioids significantly reduced. Patients with peripheral neuropathy need to be able to lie in one position without significant movement for several hours.

f. Endocrine:

To reduce cerebral edema associated with the lesion and the surgery, corticosteroids are given perioperatively. Those with adrenal insufficiency currently on steroid therapy may need perioperative stress-dose steroids. Large doses of steroids can lead to poor glycemic control, poor wound healing, and mood/mental status changes. Patients with diabetes (either insulin or non–insulin dependent) receiving steroid therapy may have even greater trouble controlling blood sugar. Tight glycemic control is important perioperatively. Insulin and oral hypoglycemics should be held during NPO status to prevent intraoperative hypoglycemia. Other acute endocrine emergencies (e.g., thyroid storm, diabetes insipidus, SIADH) should be under control before proceeding with surgery.

g. Additional systems/conditions which may be of concern in a patient undergoing this procedure and are relevant for the anesthetic plan (eg. musculoskeletal in orthopedic procedures, hematologic in a cancer patient)

Most patients undergoing awake craniotomy are relatively healthy. Unexpected "failure" (conversion to general anesthesia) in healthy patients comes from their inability to stay in one position for several hours. Those with lower back pain, cervical spine disease, fibromyalgia, restless leg syndrome, benign tremor, Parkinson's, and other chronic pain or dysarthric conditions need to be evaluated for their tolerance for positioning. Patients with skull defects (previous craniotomy, trauma) may not have the bony infrastructure for proper pinning.

4. What are the patient's medications and how should they be managed in the perioperative period?

Patients should continue taking their beta-blocker, clonidine, anticonvulsant, antacid (H2 blockers, PPIs), anxiolytic, antidepressants (with the exception of MAOIs), and asthma/COPD medications up to the day of surgery. Antiplatelet therapy and warfarin should be discontinued 7 days before surgery. Other medications should be taken up to the day before therapy and held in the morning.

h. Are there medications commonly seen in patients undergoing this procedure and for which should there be greater concern?

Patients undergoing awake craniotomy will typically receive corticosteroids, anticonvulsants, antibiotics, and diuretics (mannitol and loop diuretics). Large doses of steroids can lead to poor glycemic control, poor wound healing, and mood/mental status changes. Anticonvulsants have been shown to induce cytochromes and speed the metabolism of other certain medications, specifically nondepolarizing paralytics (paralytics are typically not used during awake craniotomies). Antibiotic allergies should be screened to prevent anaphylaxis. In patients receiving diuretics, electrolyte, acid-base, and fluid status should be followed.

i. What should be recommended with regard to continuation of medications taken chronically?

Cardiac: Beta-blockers and clonidine should be continued up to the day of surgery. Other antihypertensives (e.g., angiotensin-converting enzyme inhibitors [ACEIs]) should be held the day of surgery to decrease risk of intractable hypotension.

Pulmonary: Inhaled medications (both short and long acting) should be continued to the day of surgery, including a dose of albuterol preoperatively. Oral steroids and antileukotrienes should be continued up to the day of surgery.

Renal: Renal medications should be taken up to the night before surgery. Antirejection medications for renal transplantation should be continued through the day of surgery. Insulin and oral hypoglycemics should be held the morning of surgery (or during NPO status) to prevent hypoglycemia.

Neurologic: Anticonvulsants should be taken the day of surgery to help prevent intraoperative seizure. An intraoperative intravenous dose of phenytoin or levetiracetam may be given.

Antiplatelet: Antiplatelet therapy should be discontinued 7 days before surgery. Warfarin therapy should be discontinued 5 days before surgery or PT/INR checked the day before the procedure. Low-molecular-weight heparin (LMWH) should be discontinued the day before surgery (12 hours for prophylaxis, 24 hours for therapeutic doses).

Psychiatric: Patients with well-controlled anxiety, depression, or psychotic disorders should be maintained on their medications up through the day of surgery. Withdrawal of these medications can decrease the patient's ability to tolerate the awake portions of the procedure. MAOIs should be discontinued as they will interfere with some of the medications used during the surgery.

j. How To modify care for patients with known allergies -

Nonantibiotic, nonlatex allergies to the medications commonly used during awake craniotomies are rare. A personal or familial history of malignant hyperthermia (MH) is not concerning as most approaches to awake craniotomy avoid inhaled anesthesia (preferring TIVA) and succinylcholine (paralytics are rarely used in awake procedures and succinylcholine is generally avoided in intracranial procedures due to its effect on intracranial pressure [ICP]). Anaphylactic allergy to eggs has been associated with anaphylaxis to propofol (1% to 2%), a common agent used in awake craniotomies. In those cases, alternatives to propofol include dexmedetomidine, etomidate, droperidol, barbiturates, and benzodiazepines depending on how much sedation the patient requires. When continuous neuromonitoring is not required, inhaled anesthesia can be delivered through an LMA or endotracheal tube.

k. Latex allergy- If the patient has a sensitivity to latex (eg. rash from gloves, underwear, etc.) versus anaphylactic reaction, prepare the operating room with latex-free products.

Latex allergies do not pose a problem for patients undergoing awake craniotomy. The room can easily be prepared with latex-free products including gloves, tourniquets, Foley catheters, and anesthesia equipment. Medication vials containing latex septa can have the septum removed so that needles are not being introduced through latex.

l. Does the patient have any antibiotic allergies? (common antibiotic allergies and alternative antibiotics)

Although the cross-reactivity of penicillin allergies and cephalosporins is about 10%, the risk (especially in an unsecured airway) is considered high enough to use alternatives such as clindamycin or vancomycin.

m. Does the patient have a history of allergy to anesthesia?

Malignant hyperthermia

Documented: Avoid all trigger agents such as succinylcholine and inhalational agents. Follow a proposed general anesthetic plan: many awake craniotomies use a TIVA approach with propofol, an opioid infusion, and another agent such as dexmedetomidine. Inhaled agents are easily avoided. Succinylcholine increases ICP and is avoided in intracranial procedures. Also, paralytics are generally not necessary in awake procedures unless the airway needs emergent securing. In those cases, nondepolarizing agents are used.

Ensure that an MH cart is available [MH protocol].

Family history or risk factors for MH: Local anesthetics/muscle relaxants: Amide local anesthetics such as lidocaine, bupivacaine, and ropivacaine are used for regional and local anesthesia for awake craniotomies. Muscle relaxants are generally not necessary, but if needed for emergent airway, nondepolarizers are used.

5. What laboratory tests should be obtained and has everything been reviewed?

CBC, type and screen, chemistry panel, and coagulation panel should be obtained.

Common laboratory normal values will be same for all procedures, with a difference by age and gender.

Hemoglobin levels are obtained due to the risk of bleeding. The use of diuretics can lead to electrolytic derangements. Coagulation panel is for patients on warfarin and heparin therapy Imaging includes head CT, MRI, and fMRI. Other tests should be obtained only per the individual patient's comorbidities.

Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?

Most centers approach "awake" craniotomy with an "asleep-awake-asleep" approach. After standard monitors are placed, and intravenous access is established, patient sedation is initiated or general anesthesia is induced. During the initial "asleep" stage, there are different approaches to airway management. Lightly sedated patients without significant airway obstruction can tolerate a natural airway with nasal cannula. Alternatively, the nasopharynx can be topicalized and nasal trumpets placed. Other centers induce general anesthesia and place an LMA, or an endotracheal tube if the LMA does not sit correctly. The benefit of using an LMA is a secured airway and the ability to provide positive pressure ventilation. Disadvantages include a deeper plane of anesthesia (and increased delay to monitoring) and increased risk of coughing, laryngospasm, and emergence delirium.

The team then secures adequate intravascular access and places an arterial line and a Foley catheter, and then a scalp block is placed by either the anesthesia or surgical team. The patient is then positioned (usually in Mayfield or a similar system), providing the anesthesia team with adequate airway access and the ability to visualize and communicate with the patient. Adequate access to the patient also alleviates the sense of claustrophobia during the awake portion of the procedure. Pressure points are padded to prevent neuropathy/pain during asleep stage and to minimize pain, agitation, and movement during awake neuromonitoring. Warm blankets or a forced air warmer should be provided to prevent shivering or discomfort during awake stage. Skin incision, craniotomy, and bone flap are performed by the surgical team. Once the bone flap has been turned, the patient is awakened. It is important to remove the LMA (or endotracheal tube) deep enough to prevent coughing, laryngospasm, or emergence delirium, but at a plane that the patient can maintain the airway with minimal obstruction or hypoxemia.

Once the patient is able to communicate, the lesion is mapped and then excised while the patient undergoes continuous neurologic testing. During this stage, the patient has to be awake enough to communicate but needs to tolerate the pain/stress/positioning in order to cooperate. After neuromonitoring has finished, the patient can either be resedated or general anesthesia reinduced for closure. Risk/benefits for sedation/general anesthesia are similar to those for the original "asleep" stage; however, the closure is less stimulating than opening and the airway is more difficult to secure (due to positioning). Some surgical teams may wish to be able to communicate with the patient through closure.

Regional anesthesia

A scalp block can be performed by either the anesthesia or surgical team. A scalp block consists of 10 nerves al1ong the skull that will allow for both incisional pain and for placement of a head frame (e.g., Mayfield or Sugitta). The supraorbital, zygomatic, auriculotemporal, and lesser and greater occipital nerves are blocked bilaterally 25 to 40 mL of 0.5% bupivacaine or 0.5% ropivacaine can be used with 4 to 6 hours of anesthesia.

There is no role for neuraxial blockade in awake craniotomy.

Peripheral nerve block

A good scalp block and local anesthetic at the incision site and in the field reduce the amount of intraoperative sedation. This allows for a better neurologic exam, quicker emergence, and less risk of loss of airway/obstruction. However, local anesthetic toxicity can be a problem with large doses or if injected intravascularly. The addition of epinephrine and aspiration before injection can reduce this risk. If the block is not performed adequately, few patients are able to tolerate the procedure.

General anesthesia

General anesthesia can be useful during lining, blocking, prepping, incision, and craniotomy. It is important to decide the depth of the general anesthesia and the appropriate airway management. A lighter general anesthesia may not require an instrumented airway. However, a natural airway or simple nasal trumpet increased the risk of obstruction, hypoxemia, hypercarbia, and aspiration. Securing the airway with an LMA or endotracheal tube provides the benefit of a secured airway and the ability to provide positive ventilation. However, it does require a deeper plane of anesthesia, which can lead to emergence delirium or a delay in time to monitoring. Also, a "light" patient can buck, cough, and (in the case of an LMA) go into laryngospasm. During general anesthesia, a TIVA technique can be used, although inhaled agents can be used if an LMA or endotracheal tube is in place.

Benefits include a secured airway, ability to provide positive pressure ventilation, and control of O2 and CO2. Drawbacks are a deeper plane of anesthesia, coughing, increased ICP, laryngospasm, emergence delirium, and delay to monitoring. In addition, if the LMA does not seat, the use of an endotracheal tube may require paralysis and reversal. Also, placement of airway post monitoring may be more technically challenging than at initial induction.

Monitored anesthesia care

During neuromonitoring, the level and approach to monitored anesthesia care can differ from center to center. There are different combinations of hypnotic, anxiolytic, analgesic, and neuroleptic agents possible. The optimal combination includes short-acting agents that can be easily titrated with minimal airway obstruction. Dexmedetomidine (1 μg/kg load over 10 minutes; 0.3 to 0.7 μg/kg/min infusion), an alpha-2 agonist, provides anxiolysis and analgesia with minimal airway obstruction. It has a relatively quick (10 to 15 minutes) onset with a long (1 to 2 hours) offset. It has a profound opioid-sparing effect, allowing for smaller infusion of opioids and therefore less airway obstruction, hypoxemia, and hypercarbia. The ultra-short acting opioid remifentanil (0.01 to 0.05 μg/kg/min) can be added for extra analgesia and can be titrated to respiratory rate and end-tidal CO2 (if it is being monitored). Propofol, barbiturates, and benzodiazepines should be used sparingly during the neuromonitoring stage to prevent disinhibition and airway obstruction. Neuroleptic analgesia has been associated with dysphoria, oversedation, and hypotension.

Benefits are superior neuromonitoring, no instrumentation of airway, and less hemodynamic change. Drawbacks include inadequate sedation/disinhibition, loss of airway, obstruction, hypoxemia, and hypercarbia. It is important to titrate the agents (hypnotics, anxiolytic, opioids, neuroleptics) independently and to specific effect. If the patient is nervous, increase the anxiolytic. If the patient is in pain, increase the opioid.

6. What is the author's preferred method of anesthesia technique and why?

Cefazolin 1 to 2 g IV is the prophylactic antibiotic to be used per current guidelines. Positioning of the patient depends on the surgical approach. Type of frame, orientation of the patient, anesthesia, and surgical team should be discussed before the procedure. Incision and craniotomy should be observed so that the patient is kept at the appropriate plane of anesthesia, and awakening for monitoring is not delayed. Mapping and excision of lesion should be monitored to determine when it is appropriate to lighten or deepen the patient. The emergence from anesthesia will be determined by closure and removal of patient from surgical frame for preparation of transport to the ICU.

Intraoperatively, the type and depth of anesthesia can have profound effects on surgical field. Tight control of CO2, blood pressure, diuresis, fluid management, and the possibility of transfusion should be communicated between the surgical and anesthesia teams. Most importantly, during neuromonitoring, the patient needs to be able to communicate while tolerating the procedure. Appropriate sedation and reassurance must be facilitated to minimize postoperative neurologic complications.

Regarding the most common intraoperative complications and how they can be avoided/treated, prioritize them by urgency. Since the surgeon is directly stimulating the brain with electrodes, seizure is the number one complication. This is problematic in a patient without a secure airway who can become apneic and bite the tongue. Prophylactic anticonvulsants should be given and ice-cold saline available to pour onto the brain. Seizures can be ablated with small doses of propofol or benzodiazepines. Since the patient is awake during testing, neurocognitive function will be able to detect cerebral ischemia hopefully before a stroke can occur. Bleeding is also a risk and blood loss and resuscitation should be communicated with the surgical team. A type and screen and possibly blood products should be available, and an arterial line will allow serial hemoglobins if necessary.

Loss of airway, hypercarbia, and hypoxemia can be controlled by minimizing sedation and constant communication with patient; ultimately, the airway can be secured. Hemodynamic changes (hypotension, hypertension) are easily controlled with intra-arterial monitoring and treatment with pressors or antihypertensives.

Cardiac complications include hypotension, hypertension, myocardial ischemia, and arrhythmias, and pulmonary complications include hypoxemia, hypercarbia, aspiration, and bronchospasm.

a. Neurologic:

Neurologic complications are unique to the procedure—seizure, stroke, neurologic deficits from surgical excision, or cerebral edema.

b. If the patient is intubated, are there any special criteria for extubation?

Patients undergoing awake craniotomy generally do not remain intubated. If they are, it is usually due to an intraoperative surgical or anesthesia complication. Criteria for extubation include the patient being able to follow commands and protect the airway. If the patient should remain intubated, he or she should proceed immediately for postoperative neuroimaging.

c. Postoperative management

The goal of postoperative analgesia is to keep the patient comfortable while preventing oversedation. The scalp block should provide short-term postoperative pain control. Intravenous opioids can be administered either PRN or using patient-controlled analgesia (PCA) until the patient can take oral medication. NSAIDs should be avoided to decrease risk of postoperative bleeding and renal failure. Oral, rectal, or intravenous acetaminophen is appropriate in patients with normal liver function.

Patients should be in the ICU or equivalent setting to allow observation of any acute neurologic changes. The most common postoperative complication will be acute neurologic change due to cerebral edema or bleeding. Patients should be immediately imaged and/or sent to the operating room for decompressive craniotomy/hematoma removal. Seizures can be prevented with continued anticonvulsant therapy and treated with anticonvulsants and benzodiazepines. Tight blood pressure control can help prevent postoperative stroke. Postoperative nausea and vomiting should be aggressively treated with nonsedating antiemetics such as 5-HT antagonists.

What's the Evidence?

Bulsara, KR, Johnson, J. "Improvements in brain tumor surgery: the modern history of awake craniotomies". Neurosurg Focus. 2005;April.

Bonhomme, V, Franssen, C. "Awake craniotomy". Eur J Anesthesiol. vol. Nov. 2009. pp. 906-912.

Mack, PF, Perrine, K. "Dexmeditomidine and neurocognitive testing". J Neurosurg Anesthesiol. vol. Jan. 2004. pp. 20-25.

Sarang, A, Dinsmore, J. "Anaesthesia for awake craniotomy: evolution of a technique that facilitates awake neurological testing". Br J Anaesth . vol. 90. 2003. pp. 161-165.

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