Recibido el 26 de mayo de Aceptado el 8 de julio de On-line el 6 de septiembre de Awake craniotomy has become a common procedure and its application has been continually evolving. Anesthesia for awake craniotomy poses a unique challenge to anesthesiologists. The aims of this article are to review, under a critical perspective of the author, the current evidence and application of awake craniotomy and to briefly describe the principles of anesthetic management during this procedure.

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DOI: Abstract: Awake craniotomy is mainly used for mapping and resection of lesions in vitally important brain areas where imaging is not sufficiently sensitive. These are most commonly speech and motor areas. The awake approach has become increasingly popular with wider indications due to the advantage of better neurological and other perioperative outcomes including analge sia and postoperative nausea and vomiting.

Improvements in anesthetic agents and techniques especially LMA have made a great contribution. Frequently used medications are propofol, dexmedetomidine, and remifentanil.

Common anesthetic regi mens range from light-moderate sedation, deep sedation, or general anesthesia during the pre-mapping and postmapping phases. This approach to intracranial surgical procedure requires skill, experience, and commitment on the part of the entire OR team. This review, from the point of view of authors, discusses the indications and contraindications, benefits, anesthetic techni ques, challenges, and management, as well as potential future directions of awake craniotomy.

Los medicamentos de uso frecuente son propofol, dexmedetomidina y remifentanilo. Awake craniotomy can be defined as an intracranial surgical procedure where the patient is deliberately awake for a portion of the surgery, usually for mapping and resection of the lesion. It has a long history that pre-dates general anesthesia GA as there are many examples of paintings and descriptions of such procedures, especially trephination, dating back over a thousand years.

During the last several decades, this procedure has become increasingly popular with wider indications prompted by accumulating evidence that patients receiving awake craniotomy have better outcomes in many aspects.

The improvements in anesthetic agents and techniques, especially shorter and more dependable durations of actions, have also made a great contribution. Some aspects of awake craniotomy, including indications and contraindications, benefits, anesthetic techniques, challenges, and potential future directions are discussed. Minimally invasive procedures done through a burr hole, for example, placement of deep brain electrodes for Parkinson's Disease, are also technically awake cranioto mies, but they are not discussed in this review.

Awake craniotomy is used for any intra-axial mass lesion residing adjacent to or in eloquent brain based on pre-operative imaging, including motor, and language cortex, and also cortex responsible for other functions, for example, frontal lobe-executive functions. The lesions are primarily gliomas, cortical, and subcortical, both high and low-grade, as the survival rate is related to the extent of resection. Absolute and relative contraindications are shown in Table 1.

This is regardless of tumor site, size, and pathology; body mass index; smoking status; American Society of Anesthesiology classification; seizure duration and frequency; emotional or psychiatric history.

Table 1 Contraindication to awake craniotomy. The goal of awake craniotomy is to maximize tumor resection while preserving neurological function.

This is achieved by stimulation mapping intraoperatively in an awake patient. In addition, after awake craniotomy, patients need less intraoperative vasopressor, have less pain and less narcotic usage, and reduced postoperative nausea and vomiting. A detailed discussion of the potential disadvantages of GA has recently been reviewed. Table 2 Contraindication to awake cranniotomy. Awake craniotomy requires skill, experience, and the commitment of the entire OR team.

Pre-operative patient interview by all team members is essential in building trust and engagement. A common cause of failure is poor patient communication intra-operatively. Surgeons, anesthesiologist, and nurse provide patients with reassurance and empathy, mitigating their anxiety. Patients should be informed of constant intraoperative face-to-face interactions, and other details includ ing positioning, insertion of an indwelling urinary catheter, craniotomy noise, and mapping-related tasks.

Preoperative assessment of language function needs to be done. In general, some medications should be avoided or used cautiously, such as midazolam, atropine, and scopolamine, as they can impair neurocognitive function and lead to confusion or delirium.

However, a small dose of midazolam mg intravenous [IV] is beneficial in highly anxious younger patients with normal pre-operative neurologic function. Patients having seizure mapping should not receive any medications that suppress epileptiform activity, for example, midazolam, anti-convulsants.

There is no consensus on the need to administer anti-convulsants in patients with no prior seizures. Standard monitoring including electrocardiogram, oximetry, non-invasive and intra-arterial blood pressure, end tidal carbon dioxide, respiratory rate, and urine output is used. Monitors should be placed on the same side as brain lesion to avoid interfering with contralateral sensorimotor monitoring. Processed electroencephalogram e.

Patients usually are lateral or semi-lateral, turned 90 degrees in reference to the anesthesia workstation and facing the anesthesia team to allow face-to-face interaction and airway management. The head is usually secured in a head frame. Currently, several techniques are used in clinical practice, mainly divided into 2 groups: 1 Asleep-awake-asleep. The patient will be awake with sedation light, moderate, or deep with spontaneous ventilation for the craniotomy and closure.

With both approaches, no medications are usually administered during the mapping phase. The choice of technique must take into account team preference, tumor location, neurological status, body size, age, motivation, and medical comorbidity in addition to the patient's physical condition.

Choice of medications varies interinstitutionally and among individual teams. To achieve smooth transi tions and facilitate intraoperative mapping, anesthetics need to have rapid onset and offset, titratability, and minimal lingering effects. The most commonly used agents are propofol, fentanyl, remifentanil, and dexme-detomidine DEX , sevoflurane is also used in some institutes.

DEX has the unique advantage in that it causes only slight respiratory depression but provides some sedation and analgesia and can be used in combination with other agents or as a sole sedative. Commonly scalp nerve blockade and local infiltration along the incision line are used with a combination of lidocaine, longer acting agent bupivacaine or ropivacaine , and epinephrine. Usually there is no pain when dura is manipulated; however, irritations of nerves innervating dura in close proximity to meningeal vessels can cause pain.

This is usually managed with infiltration of local anesthetic LA along the meningeal vessels. Commonly used anesthetic regimens for awake craniotomy. DEX 0. Some patients become very disinhibited with propofol and DEX should be added or completely replace the propofol.

Deep sedation: The aim is to maintain spontaneous ventilation but with the use of an airway device for airway patency, for example, nasal trumpet s or LMA.

Anesthetic regimens for GA. Endotracheal intubation, either orally or nasally, has been used in the past. However, the transition from asleep to awake can be very challenging because of coughing and agitation. Currently, a more popular choice is an LMA, which produces less stimulation and a smoother transition. Awake phase. The goal is to transition smoothly and rapidly without agitation, confusion, or drowsiness from sedation or anesthesia to an awake patient.

The patient needs to be engaged, cooperative, pain-free, and comfort able for mapping and tumor resection. All agents are stopped, although it is sometimes useful to keep a very low dose of remifentanil 0. Pain should be managed with supplemental LA and possibly IV acetaminophen. Non-pharmacological intraoperative management should be used to reduce fear and anxiety. A sponge soaked with ice-cold water can be used to wet the patient's lips and mouth for comfort.

The patient can be allowed to move limbs and hips at appropriate times. An air blanket is used to provide either warm or cool air to maintain a comfortable temperature. Motor and sensory pathways. Awake surgery provides accurate mapping of both superficial and deep pathways of the limbs, face, and mouth.

Mapping can elicit or inhibit movements. Responses of orofacial musculature, laryngeal activity, and vocalizations can be recorded as tingling or movement, for example, withdrawal of protruded tongue, or speech arrest. The anesthesiologist should observe the patient carefully and report every movement to the surgeon, and the patient should also be instructed to report any abnormal movement or sensation.

The stimulation mapping allows not only delineation of the cortical areas but also allows the surgeon to stimulate and monitor subcortical tracts. Speech areas cannot be safely localized on the basis of anatomical landmarks. To assess speech, the Visual Object Naming Test is frequently used. The Boston Naming Test consists of 60 drawings of common objects graded in difficulty, for example, window, car, dog, guitar.

In addition, language functions can be studied with greater refinement and complexity. Intraoperative brain mapping of cortical visual cortex with subcortical mapping of visual tracts may be useful to minimize risk of permanent hemianopia in tumors located in the parieto-occipital area.

Identification of optic radiations by direct subcortical electrostimulation is a dependable method to reduce permanent injury in surgery for gliomas involving visual pathways. Challenges during the awake phase. Common challenges include hypertension, seizures, somnolence, agitation, oxygen desaturation, tight brain, and shivering.

Hypertension: This is most commonly secondary to pain, agitation, and anxiety. However, other causes should also be sought such as hypoxia, hypercapnia, and DEX associated. Treatment should focus on managing the cause. Labetalol or esmolol may sometimes be necessary. The incidence is less if the surgeon avoids stimulating an area twice in rapid succession. Continuous monitoring of electrocorticography for spikes or sharp waves within 5 seconds after each stimulation allows early detection.

Patients with a history of seizure and younger patients especially with tumors of the frontal lobe are more prone to seizures. Intravenous propofol, in small mg repeated doses, is effective, but one must be cautious so as not to produce medication-induced coma resulting in airway compromise.

IV fosphenytoin, valproate, lorazepam, or a barbiturate may rarely be needed acutely. Most resolve without adverse outcomes. Cardiac arrest and apnea may occur. Emergence agitation and delirium may occur if the pre-awake phase is with GA or deep sedation.

Contributing factors include older age; pain; disorientation; inappropriate use of naloxone, flumazenil, neostigmine, and atropine; oxygen desaturation; hypercapnia; urethral stimulation; and bladder distention.

It can be very difficult to manage, and there is no consensus on the best approach. An approach is to reinduce anesthesia with a propofol bolus mg , then administer a DEX bolus 0. Low-dose remifentanil infusion 0.


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