Awake craniotomy in brain tumors - Technique systematization and the state of the art

ABSTRACT The anesthesia for awake craniotomy (AC) is a consecrated anesthetic technique that has been perfected over the years. Initially used to map epileptic foci, it later became the standard technique for the removal of glial neoplasms in eloquent brain areas. We present an AC anesthesia technique consisting of three primordial times, called awake-asleep-awake, and their respective particularities, as well as delve into the anesthetic medications used. Its use in patients with low and high-grade gliomas was favorable for the resection of tumors within the functional boundaries of patients, with shorter hospital stay and lower direct costs. The present study aims to systematize the technique based on the experience of the largest philanthropic hospital in Latin America and discusses the most relevant aspects that have consolidated this technique as the most appropriate in the surgery of gliomas in eloquent areas.


INTRODUCTION
T he anesthesia for awake craniotomy (AC) was first performed by Sir Victor Horsley, in 1886, to locate epileptic foci with the aid of cortical electrical stimulation 1 . Wilder Penfield, a neurosurgeon and researcher, made mappings in conscious patients with severe epilepsy under local anesthesia, directly observing the brain and assessing responses to electrical stimuli. He prepared detailed reports on anatomical and functional brain correlation 2 . Since the 1980s, some authors have consolidated this technique in the treatment of neoplasms of glial origin. AC is usually carried out in the resection of tumors in eloquent brain areas, allowing the intraoperative functional mapping and identification of the regions related to language, motility, sensitivity, and vision 3,4 . There is evidence that this strategy reduces the period of postoperative recovery, hospital stay, and costs 5,6 . The main objective of AC is to minimize the risk of neurological damage, while maximizing the resection of the tumor, allowing a more radical removal, with consequent increase in survival 7,8 .

Technical note A B S T R A C T A B S T R A C T
The anesthesia for awake craniotomy (AC) is a consecrated anesthetic technique that has been perfected over the years. Initially used to map epileptic foci, it later became the standard technique for the removal of glial neoplasms in eloquent brain areas. We present an AC anesthesia technique consisting of three primordial times, called awake-asleep-awake, and their respective particularities, as well as delve into the anesthetic medications used. Its use in patients with low and high-grade gliomas was favorable for the resection of tumors within the functional boundaries of patients, with shorter hospital stay and lower direct costs. The present study aims to systematize the technique based on the experience of the largest philanthropic hospital in Latin America and discusses the most relevant aspects that have consolidated this technique as the most appropriate in the surgery of gliomas in eloquent areas.

Universitaire de Montpellier (CHU)
During a fellowship at the neuroanesthesia service of the CHU, a recognized worldwide center in the use of AC for resection of low grade gliomas, we observed a systematization of the anesthetic technique, composed of three phases: asleep, awake, and asleep.  in the spontaneous ventilation mode, with the BIS above 60-70 and the patient resumes spontaneous ventilation.
As soon as the appropriate oxygen saturation is obtained, the laryngeal mask can be removed. There is no need for oxygen supplementation during the awake phase. In this phase, some medications and measures can be adopted, aiming at the patient's comfort. If he/she experiences tremors, an intravenous dose of clonidine, 20 to 30 mcg, can be administered. In case of nausea, 6 to 10 mg of dexamethasone. If the patient has seizures, the surgeon must bathe the exposed brain with cold saline    Eventually, the patient may complain of pain related to position or even in the surgical field and if this happens, remifentanil can be infused in a low controlled dose (target TCI of 0.1 to 0.2 ng/mL). If the patient has a blood pressure cuff, it is necessary to space its measurement to every 10 minutes. Elevation in blood pressure levels is not necessarily a concern, as cerebral self-regulation is now established and the need to intervene occurs only if the patient displays measurements above 170 mm/Hg of systolic pressure.
In this case, one can introduce titrated vasodilators, such as nitroglycerin.

Third phase -ASLEEP
In this third phase, after tumor resection, we perform a new general anesthesia. After pre-oxygenation, the patient receives induction with remifentanil and Krambek Awake craniotomy in brain tumors -Technique systematization and the state of the art dexmedetomidine in the evaluation of cognitive tests 23,24 .
The occurrence of focal epileptic seizures during brain manipulation is one of the adverse events that requires rapid intervention. There is no need for prophylactic prevention, as the crisis can occur in the manipulation or traction of a certain brain structure.
However, if it occurs intraoperatively, cold saline can be instilled over the exposed brain, without the need for intravenous medication. On the other hand, if the seizure is generalized, an antiepileptic agent should be promptly administered, bearing in mind that these agents can cause sedation and respiratory depression, rendering a probable negative outcome in AC 24