**5.1 General anesthetic consideration**

Perioperative anxiety should be managed with premedication in the preoperative area. Midazolam has been demonstrated to be effective in relieving anxiety. If intraoperative ECoG is planed the dosage of Midazolam and Benzodiazepines should be reduced to minimize their depression effect on ECoG intraoperatively [47].

#### *Recent Advances in Epilepsy Surgery DOI: http://dx.doi.org/10.5772/intechopen.107856*

Anesthesia can be induced with thiopental or Propofol; these drugs rapidly induce the unconsciousness nondepolarizing muscle relaxant in the administration after induction of general anesthesia [47].

### **5.2 Awake anesthesia in epilepsy surgery**

The golden rule in epilepsy surgery is to resect the epileptogenic zone, with preservation of the neurological function [48]. The epileptogenic zone often shows no image abnormalities (FCD type I) in foci often located in functional areas, such as language or somatosensory areas. In such situations, awake surgery may be effective [48]. The main advantage of awake anesthesia is the clinical functional mapping intraoperatively under awake condition allowing the identification of eloquent area with close monitoring during resection. Positioning the patient is critical for the success of the technique "Asleep-awake-asleep." Propofol does not interfere with ECoG monitoring when disconnected 20 minutes before [24]. Certain disadvantages have been reported, such as spatial limitation of craniotomy, limited intraoperative time, inability to have ictal recording, and limitation of the patient cooperation in young patients or patients with psychological or psychiatric disorders. However, in awake anesthesia, it is imperative to psychologically prepare the patient for the procedure. It has been reported that under awake anesthesia, patients with epileptogenic foci, close to functional area, may have improved seizure control and minimal neurological complications, through intraoperative mapping information and ECoG [48].

### **5.3 Implantation of strip, grid, and depth electrodes**

Invasive monitoring tests are indicated in cases of nonconclusive noninvasive tests, with unclear lateralization or localization of the epileptogenic zone. Invasive monitoring is not an exploratory procedure, but it is a complementary test for lateralization and localization of the epileptogenic zone [49]. The most common electrodes are subdural strip and grids. Epidural electrodes are available but not widely used. The ideal electrode should be selected by epileptologist, epilepsy surgeon, and neurophysiologist together after review of the all patient data. Invasive electrodes are frequently placed bilaterally, if lateralization is unclear [50]. Strip and depth electrodes are useful for lateralization of seizure onset while grids are more helpful in localization.

Depth electrodes are more valuable for assessment of deep cortical structures, such as amygdala, hippocampus, insular, cingulum, and bifrontal cortex. They have multiple contact arrays, up to 12 nickel-chromium, or platinum contact and are commonly in use for bi-temporal mesial sclerosis, and it could be used in combination with subdural electrodes [51].

Subdural strip (**Figure 2a**–**c**) and grids (**Figure 2d**) are fine structures covered by silastic or Teflon sheets embedded in nickel-chromium or platinum. Each electrode is 2–4 mm contact in diameter with inter-electrode distance being generally 10 mm. Subdural grids are larger plates of rectangular arrays with several parallel rows up to 64 electrodes. It is an excellent choice for covering large cortical area to record inter ictal and ictal epileptogenic activity. Cortical stimulation and grid mapping are valuable to delineate the functional area and epileptogenic zone [52]. The most common complications are subdural hematoma, up to 16%, cerebral edema, (2–14%), CSF leakages (19–33%), brain edema, 2–14%, hemiparesis, 1.5% [52].

#### **Figure 2.**

*Intracranial monitoring; a & b; skull x-ray images, showing temporal bilateral intracranial strip electrodes, c; brain CT, axial cut, bone window technique, showing bilateral temporal intracranial electrodes. And d; intraoperative view showing over the brain cortex, 2 grids (4x8 &4x5 electrodes).*
