1. Advances in neuroimaging and neurophysiology are identifying resectable lesions and surgical technique to mitigate medically intractable seizure disorders.

2. Chronic anticonvulsant drug therapy has multiple side effects such as hematologic derangements and increased hepatic metabolism of drugs.

3. Intraoperative monitoring of central nervous function will significantly alter the choice of the anesthetic technique.

I. Background. Epilepsy is one of the most common neurologic disorders. There has been significant improvement in the medical management of epilepsy. Despite the development of new drugs and treatment regimens, the prevalence of pharmacologically intractable seizures is still high, leading to significant developmental delays. Intractable epilepsy is defined as failure of more than two antiepileptic drugs and having more than one seizure per month over a period of 18 months. Advances in neuroimaging techniques and electroencephalography (EEG) have provided epileptologists with surgically resectable anatomic targets that mediate some of these medically intractable seizure disorders [1]. Neurosurgeons have utilized these technologies to dramatically improve outcomes in these patients.

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II. Physiologic considerations

A. There are several features of pediatric epilepsy that differ from adult epilepsy:

1. The developing brain has a lower seizure threshold, which results in a more frequent occurrence of catastrophic epilepsy in young children.

2. In adults, mesial temporal lobe epilepsy is the most common form whereas in children, lesional epilepsy is more common. The presence of auras or focal manifestations of the seizure are relatively uncommon in the pediatric population.

3. Cerebrovascular physiology is different. Compared to adults, a larger percentage of the cardiac output is directed toward the brain, resulting in a greater cerebral blood volume in infants. Coupled with the fact that children have a lower baseline mean arterial pressure than adults, infants are at greater risk of hemodynamic instability during neurosurgical procedures.

4. Hepatic function is decreased in neonates leading to delayed metabolism of drugs. Renal function is also decreased in neonates, limiting the ability to compensate for changes in fluid and solute loads. Combined, these may alter the clearance of medications given to these patients.

B. Other considerations

1. Side effects of medical treatments.

2. Possible cranial nerve dysfunction resulting in impaired protective airway reflexes.

3. Significant comorbidities such as degenerative diseases, cerebral palsy (CP), scoliosis, inborn errors of metabolism with respiratory, myocardial effects, and hypo- or hyperglycemia.

III. Imaging techniques. Various imaging techniques are utilized to assess structural or functional epileptogenic zones. Magnetic resonance imaging (MRI) is the modality of choice for structural imaging. If the MRI is nonlocalizing and functional neuroimaging is necessary, newer modalities such as positron emission tomography (PET), single photon emission computed tomography (SPECT), MR spectroscopy (MRS), functional MRI (fMRI), magnetoencephalography (MEG), and diffusion tensor imaging (DTI) can be utilized. None of these have emerged as the best modality.

Adults in general will be able to tolerate these imaging modalities without sedation. However, since infants and patients are uncooperative, anesthesiologists. Anesthesiologists may be asked to sedate or anesthetize these children for MRI studies which can last almost one hour and require the patient, to be kept still for optimal imaging. Typically IV sedation is given to these patients, but occasionally a general anesthetic is necessary in the MRI suite to obtain optimal imaging while protecting a patient’s airway.

IV. Surgical treatment

A. Surgical treatment of seizures often involves resection of a lesion or area of cortex that has been shown to be related to seizure generation and propagation.

1. The most common location of seizure foci is the temporal lobe.

2. The temporal lobe is involved with complex partial seizures (50% of new epilepsy cases each year) that are often related to mesial temporal sclerosis or a structural lesion of the temporal lobe.

3. Approximately one-third of patients with complex partial seizures are not adequately controlled with medication alone.

4. Although many epileptogenic foci are located in the region of the temporal lobe, such foci may be located in any area of the cerebral cortex.

5. The mechanisms by which such foci contribute to seizure generation include alteration of vascularization, alteration of regional CBF, and irritation of adjacent cortex by compression or mass effect.

V. Surgical resection of seizure foci. A major concern for resection of seizure foci is to avoid harming brain tissue that controls vital functions such as motion, sensation, speech, and memory, especially if a seizure focus is adjacent to these cortical areas.

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Advances in neurophysiologic monitoring (EEG and electrocorticography [ECoG]) have increased the ability to safely perform resections in functional areas of the brain. Typically low levels of anesthetic are necessary for these types of monitoring. Sometimes, cortical stimulation of the motor cortex is performed to observe motor movement of the area of the homunculus. Here, muscle relaxants must be avoided to enable visualization of the stimulated area. Asleep craniotomy is appropriate for lesions that are not located in or deep to eloquent areas of the brain. Awake neurosurgical procedures are most important for those patients requiring interventions close to or partially overlapping eloquent brain.

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Potentially cooperative patients (adolescents and adults) can assist in determination of the limits of safe cortical resection if speech and motor functions can be continually assessed intraoperatively while performing an awake craniotomy. This technique incorporates a variety of techniques with the common goal of allowing intraoperative neurologic assessment and feedback to determine if eloquent cortex is at risk during surgical resection. Eloquent cortex is defined as a cortical region that serves a critical neurologic function such as motor, language, memory, or special sensory function. Removal of this area and loss of that specific function would have a deleterious effect on neurologic outcome. There are no randomized controlled trials comparing the safety or efficacy of these various techniques. Overall, there is a 33% to 86% seizure reduction with follow-up times of 6 months up to 7.9 years.

A. Awake craniotomy. There are different anesthetic approaches for an awake craniotomy:

1. All procedures including line placement, local anesthetic infiltration for surgical exposure, skull and dural opening, and surgical resection of the seizure focus can be done with the patient completely awake or with minimal sedation. If intraoperative electrocorticography is being utilized, benzodiazepines and barbiturates should be avoided, unless specifically accepted by the monitoring team. Patient completely awake or with minimal sedation. This requires an extremely motivated and cooperative patient.

2. Alternatively, short-acting sedatives and analgesics, such as propofol, fentanyl, or dexmedetomidine, can be titrated to unconsciousness but maintaining spontaneous ventilation for the infiltration of local anesthetic, catheter insertion for monitoring, placement of head pins, and skull opening. Then patients are allowed to awaken or kept slightly sedated for the surgical resection of the seizure focus. After surgical resection has been completed, then sedatives and analgesics can be restarted or increased for patient comfort during surgical closure.

B. Asleep–awake–asleep technique. This technique allows the painful portions of the procedure such as line placement and placement of head pins to be performed under general anesthesia. The patient does not have to tolerate a potentially uncomfortable and claustrophobic position for a long duration as a totally awake craniotomy.

1. Induce general anesthesia and maintain airway control with a supraglottic device (i.e., laryngeal mask airway [LMA]). Maintain general anesthesia for line placement, placement of head pins, and skull and dural opening.

2. The patient is then awakened, the supraglottic airway carefully removed, and resection of the seizure foci may then proceed.

3. When surgical resection has been completed, general anesthesia is again induced and the supraglottic airway reinserted for closure of the dura, skull, and skin. Following skin closure, the patient may then be awakened from general anesthesia.

4. Disadvantages of the asleep–awake–asleep approach:

a. Airway management while the patient is in head pins can be quite difficult.

b. Cervical spine injuries or scalp lacerations can occur during intraoperative emergence and reinduction should the patient cough or buck while the head is immobilized in head pins.

c. Brain swelling is a major concern. It may worsen during spontaneous ventilation from elevated carbon dioxide in conjunction with the cerebrovasodilatory effects of a volatile agent and possibly nitrous oxide. Mannitol and furosemide can be given, but the patient then becomes very uncomfortable with sensations of thirst and urinary urgency in the awake patient. Hyperventilation or Doxapram have been used, but the patients quickly tire of this effort. These maneuvers have not proven satisfactory. Slight elevation of the head of the bed, assuring the neck veins are not compromised by clothing and monitors or extreme rotation often quickly relieve the problem. If none of these maneuvers work, the patient may have to undergo general anesthesia and controlled ventilation.

d. Regardless of which technique is chosen, it is crucial for the anesthesiologist to have a discussion with the patient with respect to intraoperative needs and expectations. The preoperative evaluation is the time to determine whether or not the patient is a potential candidate to undergo an ‘‘awake’’ craniotomy.

e. In general, children who are younger than 10 years old or uncooperative patients of any age will not tolerate the awake craniotomy approach and will require general anesthesia throughout the procedure. In these scenarios, a variety of intraoperative electrophysiologic techniques such as somatosensory evoked potentials, EEG, ECoG, and motor stimulation may be used to help localize and determine the function of the site of the planned resection. If EEG studies are performed, a nitrous oxide/high-dose narcotic technique enables all potent volatile agents that depress cerebral electrical activity to be minimized by the time of study. If direct cortical motor stimulation is planned, muscle relaxants must wear off by the time of study as well. Occasionally, a seizure focus is difficult to identify intraoperatively. In these situations, hyperventilation or methohexital (in small doses, 0.25 to 0.5 mg/kg) may be helpful in lowering the seizure threshold and evoke EEG seizure activity (see chapter 26).

VI. Subdural grids and strips electrodes

A. In some patients, the seizures are so generalized that detecting the site of origin can be very difficult. When this occurs, further evaluation with perioperative intracranial EEG monitoring (‘‘grids and strips’’) may be accomplished by direct ECoG.

1. During a craniotomy under general anesthesia, leads are placed on the surface of the cerebral cortex.

2. Intraoperative EEG monitoring during the initial placement ensures that all leads are functional. The actual monitoring for seizures and mapping of seizure foci takes place over the next several days to see if a focus can be identified and eventually surgically resected.

3. The patient must be observed carefully during this postoperative period because several complications can develop with these electrodes in place. Infections can develop from a foreign body in the brain. Pneumocephalus can occur as air persists in the skull for up to 3 weeks after a craniotomy. These patients should not have nitrous oxide administered to them for subsequent procedures (i.e., seizure focus resection and/or removal of the ECoG leads) until their dura has been opened to avoid the development of tension pneumocephalus.

4. A peripheral intravenous central catheter (PICC line) can be placed during the initial surgery for placement of “grids and strips.” This is helpful as patients will receive IV antibiotic therapy during the time the electrodes are in place and avoids the discomfort of multiple IV catheter insertions.

5. These patients typically return in 1 week for repeat craniotomy for the removal of the grids and strips and resection of the seizure foci.

VII. Nonfocal surgical resection

A. When a focal resection is not possible, a lobectomy or corpus callosotomy may be attempted. Patients undergoing the corpus callosotomy are often somnolent for the first few postoperative days, particularly if a ‘‘complete’’ callosotomy is performed. This also occurs in children who have undergone insertion of multiple subdural grids and strips. It is more common for surgeons nowadays to initially perform a partial callosotomy, and to then perform a complete callosotomy if necessary. Since the surgical approach is near the sagittal sinus, this procedure can be associated with hemorrhage and venous air embolism (VAE).

Occasionally, small children will undergo a hemispherectomy because their seizures are attributed to an abnormal hemisphere that is already severely dysfunctional, such as when a hemiparesis is already present [2]. Hemispherectomies are being performed more often in younger children because it is thought to improve developmental and functional outcome later on in life.

1. Anatomic hemispherectomy consists of the resection of an entire hemisphere.

2. Functional hemispherectomy consists of a partial temporal lobectomy and disconnection of interhemispheric neural networks. The functional hemispherectomy generally involves less blood loss.

3. This procedure is usually performed when patients are very young. The intent is to permit the contralateral hemisphere to assume function of both hemispheres.

4. These can be very challenging cases for the anesthesiologist because blood loss can be significant. Multiples of estimated blood volume can be lost, and therefore adequate IV access is necessary. This can be difficult in very young children. If necessary, large-bore catheters can be placed into central veins to facilitate rapid volume resuscitation and treatment with medications.

5. One might consider the use of tranexamic acid, which has a prothrombotic effect, and may help decrease the blood loss.

6. Invasive arterial pressure monitoring is routine for such cases. Some practitioners utilize central venous pressure monitoring as well.

VIII. Vagal nerve stimulator

A. The vagal nerve stimulator (VNS) is another advance in the surgical treatment of epilepsy. Although its exact mechanism of action is not understood, it appears to inhibit seizure activity at the brainstem or cortical levels. Its placement has shown benefit with minimal side effects in many patients who are disabled by intractable seizures. It is estimated that there is a 60% to 70% improvement in seizure control in children receiving VNS, with the best results in those who suffer from drop attacks.

1. The VNS is a programmable device similar to a cardiac pacemaker, and that is placed subcutaneously under the left anterior chest wall.

2. Bipolar platinum stimulating electrode coils, which are implanted around the left vagus nerve, are connected to the generator by subcutaneously tunneled wires.

3. The device automatically activates for up to 30 seconds every 5 minutes.

4. Stimulation of the vagal nerve in this manner may affect vocal cord function, and sudden bradycardia or transient asystole has been reported but without resultant morbidity.

5. When patients with VNSs return for subsequent surgeries, it may be appropriate to deactivate the stimulator while the patient is under general anesthesia to prevent vocal cord motion. A magnet placed over the generator will deactivate the stimulator.

IX. Anesthesia issues

A. Preoperative evaluation

1. A thorough preoperative evaluation is necessary for any patient presenting to the operating suite. A history must be undertaken and a thorough physical examination must be carefully performed as many of these patients have significant comorbidities. One should pay careful attention to the respiratory and cardiac systems. Cardiac function should be optimized prior to surgery especially in older patients who may have coronary heart disease or hypertension, as there can be significant blood loss with fluid and blood administration, and swings in blood pressure that can affect myocardial contractility. A complete airway examination should be performed as some craniofacial anomalies may require special techniques to secure the airway. The evaluation should also attempt to detect underlying conditions that are leading to the seizures, as well as describing disabilities resulting from progressive neurologic dysfunction.

2. Special consideration should be given to those patients with a history of tuberous sclerosis. The intracranial lesions can lead to medically intractable epilepsy. This hamartomatous disease presents with cutaneous and intracranial lesions, with lesions infiltrating the cardiac, renal, and pulmonary systems. Preoperative electrocardiograph (EKG) and echocardiogram should perform to assess for functional defects from the possible cardiac rhabdomyomas leading to obstruction of intracardiac blood flow, dysrhythmias, or abnormal conduction pathways. Renal lesions can lead to hypertension or decreased renal function.

3. Preoperative laboratory testing should include a complete blood count to assess for a baseline hematocrit level and coagulation studies to look for any unknown coagulation disorders. This is necessary as significant blood loss can occur during the procedure and underlying coagulopathies should be corrected prior to surgery. Type and cross-matched blood should be available for these procedures.

4. The anticonvulsant medications that most of these patients require may have side effects that affect the anesthetic:

a. Abnormalities of hematologic function such as abnormal coagulation, depression of red or white blood cell production, or decreased platelet counts are especially concerning during intracranial surgery (in particular from valproic acid and carbamazepine). Steroidal NMBs are more affected by this than the benzoisoquinolones NMBs such as Atracurium and cisatracurium. Continuous quantitative NMB monitoring can facilitate safe degrees of NMB administration in anticonvulsant treated patients.

b. Alterations in hepatic function, in particular the upregulation of the cytochrome P450 system, also occur. Serum anticonvulsant levels should be determined preoperatively to detect subtherapeutic or toxic concentrations. These anticonvulsants enhance the metabolism of nondepolarizing muscle relaxants and opioids. Therefore, an increased amount of these drugs may be necessary during the surgical procedure. Newer anticonvulsants seem to have less of an effect on the metabolism of anesthetic drugs.

5. A ketogenic diet that is a high-fat, low-carbohydrate diet that promotes ketosis, has been used as an adjuvant for intractable epilepsy. This ketosis can promote a metabolic acidosis, which can be exacerbated with the use of carbohydrate-containing solutions. These patients should be given normal saline instead of lactated Ringer’s solution. Intraoperatively, these patients should have their acid base status and plasma glucose levels measured frequently.

B. General anesthesia

1. Positioning

a. The positioning of the patient will depend mostly on the location of the seizure focus.

b. Typically the seizure focus is located over one of the temporal or parietal lobes. Therefore, the most common position for this type of surgery is supine with the head turned over one shoulder. Often, the neurosurgeons place a shoulder roll to aid with optimal positioning for surgery.

c. The head of the patient is usually placed in a pinning system for the duration of the procedure. Care should be taken to assure that the endotracheal tube is properly positioned with the expectation of the head being turned laterally for the procedure. The supine position is also utilized for many other types of seizure surgery such as VNS placement, hemispherectomy, and corpus callosotomy.

d. For the awake craniotomy, the face must always be accessible to the anesthesiologist in case airway manipulation is necessary due to oversedation or the generation of a seizure. This also facilitates communication and facial observation during the neuropsychological assessment. The patient must also be in a comfortable position.

e. In many of these procedures, the site of operation is elevated (relative to the heart) to facilitate venous and CSF drainage from the surgical site. This leads to pressure decreases in the sagittal sinuses, leading to an increased chance of venous air emboli.

2. Typical surgical time

a. Intraoperative mapping of seizure foci and/or intraoperative imaging can add significant time onto the procedure.

b. The typical VNS placement takes approximately 1.5 to 2 hours.

c. A hemispherectomy is a procedure that takes several hours and can potentially last all day.

3. Induction and maintenance

a. Induction and maintenance of general anesthesia in patients who are undergoing seizure surgery is similar to that of other patients undergoing intracranial procedures. Care should be taken not to exacerbate any existing intracranial hypertension. Also, if intraoperative seizure mapping is planned, one may have to alter the anesthetic technique (see later sections for details). Discussion with the neurosurgical team is essential to generate the anesthetic plan preoperatively.

b. As mentioned earlier, consideration of the effects of anticonvulsant drugs on the metabolism of other drugs, specifically muscle relaxants and narcotics, is important to consider. It seems that first-generation antiepileptic drugs (AEDs) (i.e., phenytoin, phenobarbital, valproate) tend to have a higher potential for interactions and adverse effects due to hepatic enzyme induction or inhibition, whereas the newer AEDs have a greater safety profile and fewer drug interactions, but still can have significant adverse side effects. In terms of affecting anesthetic drug dosing, the requirements for muscle relaxants and narcotics are increased to maintain the same depth of anesthesia and muscle relaxation. Phenytoin, which is commonly given intraoperatively, can lead to hypotension and arrhythmias when given rapidly and fatalities have been reported, so careful consideration must be taken when giving drugs not familiar to the anesthesiologist.

c. The induction can be performed via either an inhalational agent or an intravenous agent, depending on the clinical circumstances. There is some concern that sevoflurane has epileptogenic potential, however it has a much faster uptake than isoflurane and less of an airway irritant, making it more ideal to perform an inhaled induction with a child. If there is concern for aspiration from vomiting due to increased intracranial pressure, a rapid sequence induction should be performed.

d. The maintenance of anesthesia can be performed with several techniques as long as one is aware of the effects of the type of anesthetic chosen. Inhaled agents can depress the metabolic supply and demand of the brain tissue, but at the same time can lead to cerebrovascular dilation. They can decrease cerebral perfusion pressure mostly by decreasing the patient’s mean arterial pressure. Inhaled agents also depress the EEG and ECoG. Intravenous agents decrease the cerebral metabolic demand but do not lead to cerebrovascular dilation. They also can depress the EEG. Opioids depress the EEG less and are good analgesics, but can lead to side effects of respiratory depression and sedation postoperatively.

e. There is much controversy as to whether anesthetic agents can increase or lower the seizure threshold. In fact, some anesthetics can produce both proconvulsant and anticonvulsant properties at different doses or with different physiologic situations. It seems that lower anesthetic doses have a proconvulsant tendency while higher doses have anticonvulsant tendencies. A drug like sevoflurane, for example, may have lead to epileptiform activity, but usually does not convert to convulsions. Low doses of propofol have definite anticonvulsant effects.

f. Adequate intravenous access is essential. These procedures are associated with significant amounts of blood loss and this tends to be the most significant intraoperative complication. Large-bore intravenous access is necessary for volume resuscitation. If those are difficult to obtain, then central venous access should be considered. Normal saline is typically used for neurosurgical procedures as it is mildly hyperosmolar and should minimize cerebral edema; however, one should realize that large quantities of normal saline are associated with hyperchloremic acidosis. Significant blood loss should be replaced with colloid such as 5% albumin or packed red blood cells. Blood loss and replacement therapy can tax the cardiovascular system. Therefore, vasopressor support with a dopamine infusion may provide some hemodynamic stability.

g. Approximately 16% of patients experience a seizure during craniotomy for seizure focus excision. Most often, this occurs as the neurosurgeon stimulates the area of interest. It may be typical of the patient’s seizures before surgery or different, depending on the relationship of the surgical stimulation to the patient’s intrinsic seizure focus. It is important to quickly communicate to the surgeon that you are observing a physical seizure. Often the seizure is localized to the face or an extremity initially but rapidly becomes generalized if not immediately interrupted. The neurosurgeon can irrigate the area with iced Ringer’s lactate to rapidly and reliably interrupt the seizure. A small bolus of propofol (10–20 mg) intravenously will stop a seizure. Both of these interventions also interrupt the electrocorticography briefly, but both are quickly completely reversible. Administration of intravenous barbiturates or benzodiazepines as anticonvulsants will interrupt the ability to stimulate and monitor for seizures for a longer time. These longer acting medications also take longer to control the seizure and may cause significant delays until effective monitoring can resume. If the patient goes into a persistent seizure you must protect them from personal injury, protect the airway and administer medications such as thiopental, propofol or benzodiazepines.

C. Monitoring. Monitoring for these patients is similar to that for other patients undergoing intracranial procedures:

1. Invasive BP monitoring is almost always used for intracranial procedures to ensure adequate mean arterial pressure and therefore cerebral perfusion pressure throughout the case. An arterial line also allows for serial blood gas sampling and lab draws. VNS placement typically does not require invasive BP monitoring.

2. Often it is useful to use a precordial Doppler to monitor for VAE. The precordial Doppler in conjunction with end-tidal CO₂ monitoring should enable the practitioner to detect minute VAE early enough before any significant hemodynamic instability can develop. The probe is best placed on the anterior chest, usually over the right of the sternum at the fourth intercostal space (see chapter 22).

3. A variety of neuromonitoring techniques are often used during these procedures. These techniques may include evoked potential monitoring, EEG, ECOG, and motor stimulation. If an awake craniotomy is performed, the patient will act as her or his own monitor.

4. Blood glucose levels should be monitored intraoperatively as well. Neonates with underdeveloped gluconeogenesis may require glucose to maintain IV fluids; however, this should be done cautiously as hyperglycemia should always be avoided in neurosurgical procedures as it may exacerbate neurologic injury if ischemia should develop.

5. Continuous monitoring of NMB as the response to NMBs is quite unpredictable.

D. Neuromonitoring. Anesthetic goals for epilepsy surgery are similar to other similar neurosurgical procedures (i.e., craniotomies). Detail of the age specific differences in the ECoG are discussed in Chapter 26. During seizure surgery, however, various modes of intraoperative neuromonitoring are often used to aid in delineation of seizure foci. Such techniques may involve ECoG, cortical stimulation, or electromyography. It is important to discuss the requirements of intraoperative mapping and neuromonitoring with the neurosurgeon, neurologist, and neurophysiologist in order to tailor the anesthetic technique. For example, if it will be necessary to induce seizure activity, long-acting agents that elevate the seizure threshold may be avoided. In the case of concurrent ECoG monitoring, one may minimize the dosage of a benzodiazepine given preoperatively for the anxious child. Occasionally, it may be necessary to induce seizure activity (i.e., administration of methohexital) to help locate seizure foci.

E. Postoperative considerations

1. For patients who have undergone primary resection of a seizure focus, or temporal lobectomy, the postoperative considerations are similar to those other patients who have undergone craniotomy. Typically, these patients are sent to the intensive care unit (ICU) postoperatively for serial neurologic examinations and invasive hemodynamic monitoring. Low dose dexmedetomidine (alpha 2 agonist) decreases the narcotic requirements greatly and the patients are much more calm and more readily arousable than if only narcotic sedation is utilized.

2. Monitoring for seizure activity should continue and a plan for treatment should be agreed upon. When patients have subdural electrodes (grids/strips) placed, the goal is to have the patient seize postoperatively in a controlled and monitored setting in order to generate a map of the seizure focus. However, there should be a plan in place to address longer, uncontrolled seizure activity that does not cease on its own.

a. These patients may be somewhat somnolent depending on the number of electrodes left in place with higher numbers seeming to increase somnolence.

b. Pain may be more significant in these patients and analgesic technique should be adjusted correspondingly. Typically, intravenous opioids are titrated to treat pain. However, opioid-induced respiratory depression can lead to hypoxemia and hypercarbia. If the patient requires large amounts of opioids and is old enough to do so, patient-controlled analgesia (PCA) can be administered.

c. In addition, these patients will need continued IV antibiotic coverage while the electrodes are in place (which may be up to 2 weeks). Our practice is to place a PICC line in these patients during the same anesthetic to ensure longer-term IV access. The PICC line can be left in place while the patient is in the hospital and all medications administered through it. When the patient returns to the OR for the definitive resection, the PICC line may be used for induction of anesthesia.

3. Patients who undergo hemispherectomy or corpus callosotomy are often extremely somnolent for the first several days postoperatively. Therefore, the patient is often kept intubated at the conclusion of the surgical procedure. These patients are commonly taken to the ICU intubated and will most often be ready for extubation within 1 to 2 days of surgery.

4. These intracranial procedures can be associated with the syndrome of inappropriate antidiuretic hormone secretion (SIADH) leading to hyponatremia, or diabetes insipidus or cerebral salt wasting syndrome leading to hypernatremia.

5. Patients undergoing VNS can be sent home the day of surgery as long as there are no anesthetic or surgical concerns after the procedure has been completed.

CLINICAL PEARL

1. These surgeries in general are associated with significant blood loss. One should always be prepared with adequate intravenous access and blood products for resuscitation of the patient.

2. Depending on the surgical conditions, different types of neuromonitoring may be implemented. It is important to know ahead of time if the surgeons plan on using EEG, ECOG, motor stimulation, or the neurologic examination from an awake patient. The type of anesthetic must be altered to optimize the conditions for adequate neuromonitoring.

3. Given the numerous AEDs and the differing effects on metabolism of other drugs, the anesthesiologist must be attentive to the effects they can have on anesthetic agents, particularly muscle relaxants and narcotics. Careful attention should be applied toward monitoring for muscle relaxation (when used) and depth of anesthesia as these can be altered when compared to other types of surgery.

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