Introduction

Tumor resection is a balance between extensive tumor removal and the preservation of brain function. The use of preoperative functional MRI, neuronavigation, fluorescent dyes, intraoperative magnetic resonance imaging (iMRI), and intraoperative stimulation mapping (ISM) helps delineate tumors from the functional brain. In awake craniotomy, the patient participates in ISM and neuropsychologic testing during tumor resection. Some centers use both iMRI and ISM to improve resection and minimize functional impairment.

Indications

The awake technique is the gold standard for tumor resection near “eloquent areas” of the brain. ^, “Eloquent areas” of the brain if injured lead to motor, sensory, vision, hearing, speech, or language processing deficits. Anatomically, “eloquent areas” of the brain include the primary motor cortex (precentral gyrus), primary sensory cortex (postcentral gyrus), primary visual cortex, primary auditory cortex, left posterior inferior frontal gyrus (Broca’s area), and left posterior superior temporal gyrus (Wernicke’s area). Tumors in or near the primary motor cortex, primary sensory cortex, or speech areas are often resected under awake conditions. Tumor location is the primary driver for choosing an awake craniotomy technique. During the awake portion of the craniotomy, patient participation in neurocognitive testing assists the surgeon in identifying functional areas of the brain, facilitating a more complete resection of the tumor while preserving brain function. A meta-analysis of 90 published reports of glioma resection with and without ISM concluded that glioma resections using ISM are associated with fewer late severe neurologic deficits and more extensive resection, and they involve eloquent locations more frequently.

Preoperative assessment by an anesthesiologist should occur at least 1 day prior to the planned surgery. A thorough preoperative evaluation and discussion between the anesthesiologist assigned to the case and the patient is strongly recommended to build rapport and trust, document preexisting neurologic deficits, prepare the patient for the surgical events, and appropriately set patient expectations. The discussion must include expected intraoperative body positioning, the possibility of unpleasant sensations (e.g., hip or shoulder pain, dry mouth, headache during resection, nausea, unfamiliar noises from surgical equipment), the tunnel-like view the patient will have due to surgical draping, strategies used to keep the patient as comfortable as possible, and the possibility that an awake technique may be abandoned if safety becomes compromised. The anesthesiologist must assess patient motivation, temperament, ability to cooperate and communicate, and preexisting comorbidities when considering the awake technique. Patients who are claustrophobic, severely anxious, or diagnosed with a psychiatric illness may not be able to stay calm and cooperate during the awake portion of the case. Patients with substantial speech impairment or expressive aphasia may not have a consistent baseline during preoperative testing, making intraoperative testing less reliable. A patient with a difficult airway or sleep apnea poses significant challenges for adequate oxygenation and ventilation.

Techniques

There are two well-described anesthetic techniques for awake craniotomy: asleep-awake-asleep and monitored anesthesia care. The primary differences between the two techniques involve anesthetic management prior to the intraoperative neuropsychologic testing. The asleep-awake-asleep technique includes induction of anesthesia, placement of a supraglottic airway, controlled ventilation during craniectomy and dural opening, awakening, and removal of the supraglottic airway followed by neuropsychologic testing. The advantages of the asleep-awake-asleep technique include a rest period for the patient prior to awake testing and tumor resection, control of ventilation to avoid hypoventilation and brain swelling, and reliable pain control during surgical opening. The monitored anesthesia care technique includes minimal sedation prior to surgical opening with the advantage of avoiding an abrupt, potentially tumultuous transition from fully anesthetized to fully awake. The MAC technique by definition includes spontaneous ventilation, which can lead to hypoventilation, increased CBF, and brain swelling. A third technique, the awake-awake-awake technique, relies on medical hypnosis to avoid all sedation.

Premedications

The choice of premedications should focus on preventing nausea, decreasing the risk of aspiration, and providing analgesia. A common regimen includes oral acetaminophen and aprepitant, and intravenous famotidine. Although transdermal scopolamine is an effective antiemetic, the side effects of mydriasis, blurred vision, and dry mouth are not well suited for patients undergoing awake craniotomy. We avoid administering benzodiazepines to decrease the likelihood of delayed awakening and delirium. However, if the monitored anesthesia care technique is planned, midazolam is commonly administered.

Preinduction

Awake positioning is critical for the success of awake craniotomy. Surgeons should place the patient in the position required for surgery. Significant effort is required to ensure maximum patient comfort in the surgical position prior to induction. Specific areas of concern include the position of the head, neck, and dependent shoulder and hip. The use of Mayfield pins, a three-pin head fixation system, is very common. Although rigid head fixation occurs after induction, the anticipated surgical position of the head and neck should be mimicked during preinduction positioning. Although head position is primarily determined by the required surgical exposure, the patient’s gaze direction must allow for participation in neuropsychologic testing. The neck position must allow for effective mask ventilation, insertion of a supraglottic airway, and airway rescue with a video-assisted bronchoscope. Reducing the pressure on the dependent shoulder and hip improves patient comfort, tolerance, and participation in testing. We use a combination of gel rolls, pillows, and foam padding to place the patient in a comfortable “sloppy lateral” position.

Induction

For the asleep-awake-asleep technique, intravenous induction with fentanyl 0.5–1 µg/kg, lidocaine 1.5 mg/kg, and propofol 1.5–2 mg/kg is standard. Following successful mask ventilation with the head and neck in the surgical position, rocuronium 0.6 mg/kg can be administered but this is not mandatory. Soon after induction, infusion of propofol 25–100 µg/kg/min and remifentanil 0.01–0.1 µg/kg/min are started. For younger or more anxious patients, the addition of dexmedetomidine 0.1–0.5 µg/kg/h is useful. Volatile anesthetic can be used if the end-tidal concentration is kept under 0.5 MAC. A supraglottic airway with a port for a gastric tube is placed, and the ability to provide adequate minute ventilation is verified. The inability to maintain an adequate seal or to provide tidal volumes of 4–6 mL/kg at peak inspiratory pressure <20 cmH ₂ O indicates a poor fit or malposition of the supraglottic airway and will lead to hypoventilation. This problem must be addressed before proceeding with the surgery. The gastric tube should be advanced to a depth indicative of intragastric placement. If oral premedications have been administered, suctioning of the gastric tube is delayed until just before waking up. Following placement of the supraglottic airway, the eyes should be protected with tape to ensure complete closure. An eye lubricant is not used to preserve the clear vision needed for ISM.

For the monitored anesthesia care technique, sedation is initiated with infusions of remifentanil 0.01–0.1 µg/kg/min and either propofol 25–100 µg/kg/min or dexmedetomidine 0.1–0.5 µg/kg/h. The patient’s nose can be sprayed with lidocaine and a soft nasal trumpet coated with viscous lidocaine inserted into the most patent nostril. Supplemental oxygen is supplied by attaching the anesthesia circuit to the nasal trumpet.

Regardless of the anesthetic technique, a bilateral scalp block is performed and includes injection of ropivacaine 0.5% with epinephrine 1:200,000 at the supratrochlear, supraorbital, zygomaticotemporal, auriculotemporal, lesser occipital, and greater occipital nerves. A scalp block provides analgesia for both Mayfield pin placement and skin incision. Many surgeons inject additional local anesthetics with epinephrine along the planned incision site.

Head Fixation

The three-pin Mayfield head fixation system is widely used in craniotomies. Shen et al. describe an awake craniotomy protocol used at Stoney Brook that eliminates the need for rigid head fixation using a frameless Brainlab skull-mounted array for stereotactic navigation. The authors describe the use of a soft foam pillow instead of rigid fixation and improved patient comfort and easier access to the airway for the anesthesiologist as advantages.

Access and Monitoring

A second peripheral intravenous line, an arterial catheter, a Foley catheter, and, if available, a BIS monitor should be placed. The intravenous lines and arterial catheter should be placed on the arm ipsilateral to the surgery so that sensory and motor testing on the contralateral side are unimpeded by invasive lines.

Intraoperative Management

Following line and catheter placement, surgeons use neuronavigation, and the patient is prepped and draped. The surgical drapes must be secured in a way that allows a clear visual connection between the patient’s eyes and the anesthesiologist and neuropsychologic testing team. The use of surgical drapes containing clear panels allows room light to illuminate the patient’s face. A small microphone is secured close to the patient’s mouth to facilitate patient-to-surgeon communication.

After the dura is opened, the surgeon will request that the patient be awoken. Intravenous ondansetron should be administered, and a dose of intravenous acetaminophen can be considered. The anesthesiologist discontinues all anesthetic infusions and volatile agents. If a BIS monitor is being used, the anesthesiologist can use the BIS as a rough guide for when the patient is nearing an awake state. If rocuronium has been administered, the response to a train of four should be measured. Reversal of muscle relaxant is indicated if the response is anything less than 4/4 without fade. The patient can be placed on pressure support to elicit spontaneous respiration. The anesthesiologist is positioned in direct line of sight with the patient and should firmly hold each of the patient’s hands. The anesthesiologist should begin talking to the patient well before there is objective evidence of the awakened state. Use of a reassuring, repetitive phrase to the patient helps to orient the patient as to where they are for example, “You are in the operating room. Surgery is going well. Don’t move. Stay very still. It is time to wake up, just like we talked about. Open your eyes. Squeeze my hands.” When the patient is breathing spontaneously with adequate minute ventilation and following commands, the supraglottic airway can be removed. Typically, patients take an additional 5–10 min after airway removal to be able to participate in testing. During this time period, blood pressure often rises and requires treatment to maintain a systolic blood pressure (SBP) of <140 mmHg. Patients may report discomfort that should be promptly addressed with minor repositioning, massage, or a low-dose infusion of remifentanil. Anxiety can be alleviated in most cases with a low-dose infusion of dexmedetomidine. Small ice chips are immensely helpful in treating dry mouth, and patients are grateful for the “treat.” When the patient is fully awake, testing can begin and may include object naming, sentence completion, action naming, simple math problems, motor tasks, and sensory identification. We have a neuropsychology team in the operating room to conduct the testing. The advantages of having such a team include quantifiable measurement, precise identification of deficit (e.g., syntax error versus hesitancy versus speech arrest), potentially shorter surgical times, and more frequent gross total resection. ^, Additionally, when a neuropsychology team conducts intraoperative testing the anesthesia team can focus on the physical and mental well being of the patient. As the awake time period extends, patients often become fatigued and increasingly notice the discomfort of positioning. The challenges for the patient in enduring through a long awake period cannot be overstated. Throughout the awake period, the anesthesiologist attends to the patient’s needs, provides reassurance, addresses pain issues, and communicates with the surgical team regarding the patient’s ability to continue in the awake state. At the completion of the resection, the surgeon will inform the anesthesiologist that the patient may “go back to sleep.” The anesthesiologist may decide to induce general anesthesia, reinsert the supraglottic airway, and resume controlled ventilation. Alternatively, the anesthesiologist may decide to sedate the patient and allow spontaneous respiration without an airway throughout the closing period. Factors influencing the anesthesiologist’s decision include the adequacy of the patient’s natural airway, hemodynamic status, anticipated length of closure, and need for additional intraoperative imaging.

Intraoperative Challenges

The intraoperative management plan must consider several common events. Intraoperative seizure is an emergency situation during awake craniotomy and must be managed immediately. Seizures increase cerebral oxygen demand and can cause uncontrolled movement, leading to patient injury. Uncontrolled movement of the head from a seizure can lead to scalp laceration at the pin sites or dislodgement of the head from the head fixation. Ice cold saline placed on the brain by the surgeon during seizures often stops the activity. If this intervention is unsuccessful, propofol is often effective; however, propofol depresses respiration and can lead to patient apnea. Mask ventilation or emergency placement of a supraglottic airway may be necessary; hence positioning is important at the beginning of the case to enable mask ventilation of the patient in the surgical position.

Most patients undergoing awake craniotomy have some level of anxiety, and some patients, upon awakening, develop severe anxiety and simply cannot tolerate the demands of the situation. Low-dose dexmedetomidine can be immensely effective in controlling anxiety. If this intervention fails, and the patient’s anxiety makes useful testing nearly impossible, the patient should be returned to an anesthetized state. This scenario should be discussed with every patient scheduled for awake craniotomy.

Many centers use iMRI in combination with the awake craniotomy technique. The use of iMRI usually includes a preincision iMRI, mapping and resection under awake conditions, postresection iMRI with contrast, additional resection if needed, and closure. The use of iMRI precludes the use of a BIS monitor or Foley catheter containing a temperature probe. iMRI following initial resection can be performed with the patient sedated and spontaneously breathing without an artificial airway or after insertion of a supraglottic airway. The significant distance between the anesthesia team and the patient undergoing the iMRI can create a tenuous situation if the patient is sedated without a supraglottic airway. Airway obstruction, respiratory depression, and inadequate sedation leading to movement or anxiety can create a dangerous situation for the patient, and we routinely reinsert the laryngeal mask airway (LMA) and control ventilation for the postresection iMRI.

Vascular Access and Monitoring

Vascular access for patients undergoing craniotomy is dictated by the anticipated blood loss. For the majority of cases, it is sufficient to have two intravenous (IV) lines, preferably with one being a large-bore IV line. If the semisitting position is planned, blood loss is expected to be significant or peripheral access is difficult or impossible, placement of a central venous catheter (CVC) should be strongly considered. Otherwise, a CVC is not necessary. If a CVC is needed, placement in the subclavian vein is preferred over either the internal jugular or femoral veins due to the potential for compromised cerebral venous drainage and infection, respectively.

For intraoperative monitoring, beat-to-beat blood pressure measurements using an arterial line are routine. An arterial line also provides ease of access to blood samples when intraoperative and postoperative laboratory studies are needed. Craniotomy patients benefit from meticulous blood pressure control and hemodynamic stability to minimize fluctuations in CBF that may contribute to changes in ICP or cerebral ischemia. Therefore avoidance of both hypotension and hypertension is important. Arterial hypotension, defined as SBP less than 90 mmHg or MAP less than 70 mmHg, may decrease cerebral perfusion and increase the risk of intracranial ischemic injury. Consequences of arterial hypertension, defined as SBP greater than 140 mmHg or MAP greater than 110 mmHg, include risk of surgical bleeding and increased CBF that may contribute to brain tissue swelling. In treating aberrant blood pressure, consider using vasopressors or antihypertensive medications that are short acting, since surgical stimulation may vary widely during craniotomy. Generally, noxious stimuli are more prevalent during skin incision and closure, bone flap removal and replacement, and dural opening and closure than during the time of tumor resection when stimulation is usually minimal. However, if tumor resection involves areas adjacent to intracranial blood vessels or the dura, elevations in blood pressure and heart rate may occur. Given this dynamic surgical environment, short-acting agents allow the provider to adjust the treatment administered to meet the patient’s ever-changing needs. Rhythm disturbances may occur during craniotomy, which warrants vigilant monitoring. Most notably, asystole and bradycardia resulting from surgically induced vagus nerve stimulation or trigeminal cardiac reflex during craniotomy have been reported in the literature; treatment is with cessation of the stimulus. If local anesthetics are used, toxicity may occur that could induce both rhythm disturbances and hemodynamic instability. The treatment for local anesthetic toxicity is administration of intralipid and supportive care until the baseline cardiac rhythm and blood pressure are restored.

Measuring the depth of anesthesia using noninvasive tools such as the BIS brain monitor system should be considered when TIVA is used. However, care must be taken to avoid encroaching on the surgical field when placing the BIS electrode sensor on the patient’s forehead.

Hyperthermia in the setting of an impaired brain or one at increased risk of injury is associated with poor outcome and higher mortality. Additionally, hyperthermia, regardless of severity or duration, can cause both neurologic and cognitive impairment that may persist even after normothermia is established. Mechanistically, hyperthermia negatively impacts the cell structure and function of neurons and can exacerbate neuronal injury resulting from other processes such as ischemia. ^, Intraoperative hyperthermia usually results from aggressive patient warming and thus can be avoided by carefully monitoring core temperature and discontinuing active warming and/or removing excessive blankets and drapes when indicated. Ideally, core body temperature for patients undergoing craniotomy should be maintained between 36°C and 37°C.

Head Pinning and Surgical Positioning

A scalp block (discussed later) or infiltration of the pin sites with local anesthetic can dramatically decrease the hemodynamic response to placement of the head fixation pins. If the use of a local anesthetic adjuvant is not possible, pretreatment with propofol, an opioid, nicardipine, and/or esmolol should be administered to control the blood pressure and heart rate during the placement of head pins. Regardless of the drug class used to control the response to the head pins, short-acting agents provide adequate depth without the risk of prolonged hypotension.

Surgical positioning concerns specific to craniotomy include head positioning to optimize surgical exposure and use of the semisitting position. For craniotomy patients positioned horizontally, either supine or in the lateral position, head rotation should be limited to avoid compromising the patient’s airway or impeding cerebral venous drainage. As discussed above, the semisitting position is used for surgeries involving tumors in the posterior fossa and cervical region. In addition to providing the neurosurgeon better access to these tumors, the semisitting position facilitates cerebral venous and cerebral spinal fluid (CSF) drainage; consequently, surgical exposure is improved, especially for deeper structures. Anesthetic advantages of the semisitting position include better access to the patient’s airway, better access for neuromonitoring, and in the case of a cardiopulmonary event easier access to perform chest compressions. The primary risks of the semisitting position are intraoperative VAE, paradoxical air embolism, and hypotension.

The most vulnerable time for VAE occurrence is from skin incision to dural opening. From a surgical standpoint, preventative measures for VAE include applying bone wax along the borders of the intact bone when the bone flap is removed, intermittently irrigating the surgical field, and avoiding dural retraction. Signs of VAE include a millwheel murmur from the Doppler, decline in end-tidal carbon dioxide, and potentially a decline in blood pressure. If VAE is suspected, the immediate goals are prevention of further entrainment of air, identification of the source of the air, maintenance of hemodynamic stability, and repair of open vessels. Placing the patient’s bed into the steep Trendelenburg position, initiating positive end-expiratory pressure, and manually compressing the jugular veins increase intracranial venous pressure and prevent the ongoing aspiration of air. If present, the CVC should be used to aspirate any air bubbles that may be present. If hemodynamic compromise occurs, supportive care with fluids and positive inotropic agents should be employed.

Brain Relaxation and Optimizing Surgical Exposure

Intraoperative brain relaxation, defined as the volume of brain tissue relative to the intracranial space in an open cranium, is an important determinant of surgical exposure and overall operating conditions. A variety of strategies may be employed to achieve brain relaxation, a state in which the intracranial tissue is soft, lacks swelling, and the ratio of tissue content to cranial volume is optimized. These strategies include hyperventilation, administration of a hyperosmolar treatment along with judicious use of fluids, placing the patient in the reverse Trendelenburg position, administration of a steroid, and minimizing or eliminating the use of volatile anesthetics.

Hyperventilation results in hypocapnia-induced cerebral vasoconstriction, which decreases cerebral blood volume (CBV) and helps to curtail tissue swelling. Because the reduction in CBV is associated with reduced CBF, the risk of ischemia-induced brain injury may be increased with hyperventilation. Current recommendations are to use hyperventilation only when there is a clinical indication and only as a temporizing measure when brain swelling is present. ^, Other side effects of hyperventilation include respiratory alkalosis and potential hypokalemia. Therefore, in the setting of hyperventilation, arterial blood gas (ABG) tests should be performed periodically to monitor the partial pressure of carbon dioxide (Pco ₂ ), pH, and potassium level. If utilizing hyperventilation, the lowest recommended arterial Pco ₂ value to target is 30 mmHg; below this threshold, the risks of hyperventilation may outweigh its benefits.

Administration of a hyperosmolar fluid, such as mannitol or hypertonic saline, also aids in brain relaxation. Hyperosmolar agents create an osmotic gradient that displaces free water from brain tissue to the intravascular space, effectively reducing brain tissue edema. However, in the setting of intracranial hypertension, hyperosmolar therapy may cause normal tissue to contract and exacerbate any midline shift or herniation. Risks specifically associated with the use of mannitol include severe diuresis, renal dysfunction, electrolyte disturbances, and transient changes in preload, afterload, and cardiac output. Fortunately, these side effects are self-limiting in patients with preserved cardiac and renal function. If there is a disruption in the blood-brain barrier, mannitol may worsen cerebral edema and thus should be avoided in these patients. Potential adverse effects of hypertonic saline include hypernatremia, hypokalemia, central pontine myelinolysis, and pulmonary edema. ^{, ,} In addition to utilizing hyperosmolar treatments, limiting the use of hypotonic fluids can help minimize brain swelling. Although furosemide has traditionally been used to facilitate brain relaxation, recent studies have not demonstrated its efficacy in reducing cerebral edema either alone or in conjunction with hyperosmolar fluids. ^,

When feasible, placing the patient in reverse Trendelenburg position can facilitate brain relaxation. In this head-up tilt position, the effect of gravity will translocate cerebral spinal fluid from the intracranial space to the extracranial subarachnoid space and enhance cerebral venous drainage to effectively reduce CBV; as a result, the intracranial tissue volume will be reduced. The risks associated with reverse Trendelenburg include systemic hypotension, cerebral hypoperfusion, VAE, and pneumocephalus. ^{, ,} Limiting the head-up tilt position to 30 degrees or less can reduce ICP and minimize cerebral edema without affecting brain perfusion. ^{, ,}

Administration of glucocorticoids in patients undergoing intracranial tumor resection has become a standard practice to reduce vasogenic edema from tumor-associated disruption of the blood-brain barrier, primarily affecting the white matter. Although the exact mechanism is not known, the effectiveness of glucocorticoids in facilitating brain relaxation is well established. The risks of steroid treatment include hyperglycemia and potential immunosuppression that may negatively impact the patient’s postoperative outcome and cancer prognosis. ^{, ,}

As discussed above, TIVA, consisting primarily of propofol, reduces ICP through its effect on CBF and CBV compared to volatile anesthetics. This reduction in ICP may translate to improved brain relaxation in the open cranium during craniotomy. Despite the generally accepted premise that TIVA has favorable effects on brain swelling, findings from clinical studies on anesthetic techniques and brain relaxation have not demonstrated a distinct advantage of one anesthetic agent over any other. ^, Because inhalational anesthetics have a dose-dependent effect on cerebral vasodilation, intravenous anesthetics may confer benefit as an adjunct to limit the dose of the volatile agent to <0.5 MAC.

Emergence From Anesthesia

Emergence from anesthesia is a critical period in which there is a greater chance of intracranial hemorrhage. To reduce this risk, meticulous blood pressure control is crucial, since both hypertension and tachycardia usually occur as the patient awakens. Although these hemodynamic derangements may be brief in duration, they are often severe enough to necessitate treatment. Incremental doses of a short-acting antihypertensive and beta blockers, such as nicardipine and esmolol, respectively, can be used to rapidly treat hypertension and tachycardia while minimizing the risk of prolonged hypotension. For patients with a history of severe hypertension that is refractory to treatment, a continuous infusion of nicardipine may be required and should be titrated to effect. Persistent hypertension that is observed after the extubation of the patient should be treated with a longer-acting antihypertensive medication. The desirable blood pressure and heart rate parameters outside of which the patient will require treatment should be determined based on the patient’s baseline preoperative values, comorbidities, and surgical determinants.

An intracranial bleed may also be caused by elevated ICP from coughing or retching during emergence due to endotracheal tube-induced stimulation. Patients with increased airway sensitivity (e.g., smokers and asthmatic patients) or in whom there is an increased risk of surgical bleeding should be considered for either deep extubation or LMA exchange. Deep extubation can decrease the risk of coughing, retching, and bronchospasm, but also has its own risks. Contraindications to deep extubation include known increased risk for aspiration, suspected or proven difficult mask ventilation or intubation, and risk of pneumocephalus if positive pressure mask ventilation is required. Deep extubation leaves the patient at some risk for aspiration because the endotracheal tube is removed before full airway reflexes have returned. Laryngospasm after deep extubation is common and can occur as the patient passes through stage two of anesthesia. Intraoperative fluid administration can cause airway edema, making deep extubation unwise.

An alternative to deep extubation is LMA exchange to facilitate smooth emergence. Similar to deep extubation, LMA exchange requires removal of the endotracheal tube, while the patient is still fully anesthetized. However, after the patient is extubated, an LMA is placed, and the patient can be mechanically ventilated during emergence from anesthesia. The LMA is subsequently removed once the patient meets the extubation criteria. Because LMA is less invasive and better tolerated in most patients than an endotracheal tube, its use may alleviate coughing and retching that might otherwise occur. The main advantage of this technique over deep extubation is the presence of a secured airway. However, it is important to recognize that deep extubation is still required, thus presenting the same risks—aspiration, laryngospasm, and hypoxia. Additionally, there is a potential that the LMA may not seat appropriately to allow adequate ventilation, in which case reintubation with an endotracheal tube is needed.

In addition to a smooth emergence, rapid wake-up from anesthesia is desirable in patients undergoing craniotomy. Intraoperatively, anesthetics and analgesics should be titrated to ensure that patients are awake and alert after extubation, allowing for adequate assessment of the neurologic status. Prolonged sedation from anesthesia can mimic the signs and symptoms of surgical complications and is problematic. While prolonged sedation will resolve with time, the delay in treatment for neurosurgical complications may be life threatening.

Scalp Block

As discussed above, patients undergoing craniotomy present a unique challenge in anesthetic management wherein tight regulation of blood pressure and heart rate is balanced with the need for rapid and smooth emergence. To address such challenges, the use of a regional block, termed a scalp block, can be incorporated in the anesthetic care plan as part of a multimodal approach to perioperative pain control in patients undergoing supratentorial craniotomy. A scalp block selectively targets up to 12 sensory nerves (6 on each side) innervating the forehead and scalp. These include the supraorbital, supratrochlear, zygomaticotemporal, auriculotemporal, greater occipital, and lesser occipital nerves ( Fig. 19.2 ).

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