**5.2 Local anesthesia and regional block**

Regardless of the anesthetic modality, local anesthesia must also be used. Bupivacaine, mepivacaine, levo-bupivacine, and lidocaine are the local anesthetics most frequently used in skull surgery. Lidocaine is very useful for dura mater infiltration, but it increases the risk of seizures. The use of an anesthetic with a vasoconstrictor reduces the risk of bleeding, ensures a prolonged duration, and reduces the risk of toxicity (once infiltrated, it is necessary to wait 15 minutes to rule out acute toxicity). The total amount of local anesthetic use during the procedure will be determined by the patient's weight, comorbidities, and the concentration of the anesthetic.

Bearing in mind the locations for local anesthesia, the infiltration of the head support anchor points and infiltration of the skin incision is recommended. If we want to achieve a selective blockade (more effective for pain control during the procedure), the following locations should be also infiltrated:


In long-term procedures, the appearance of pain in the temporal area and its relationship with the manipulation of the dura mater are common. In these cases, additional infiltration of the zygomatic-temporal branch is recommended.

#### **5.3 Brain mapping**

Direct cortical and subcortical stimulation is used to identify the cortical regions and tracts involved in the functions we are interested in. This stimulation produces depolarization of a specific region, leading to a neuronal excitation by current diffusion, both anti- and orthodromic. The stimulation can be performed using bipolar or monopolar probes. Bipolar stimulation is performed using a pair of 2-mm-tip stimulators with 5 mm of separation between tips. This is considered a more precise method for stimulation than monopolar (2–3 mm single-tip stimulator). However, when a more precise sensorimotor mapping is going to be performed, monopolar stimulation is preferred, because the use of bipolar probes may result in ambiguous spatial distribution.

The stimulation is initiated from 1.5 to 2 mA and progressively increases 0.5 mA to achieve 6 mA of stimulation current when no response is observed. The generator supplies a constant current with biphasic quadratic waves of 1.25 ms in 4-second trains at 60 Hz. Subcortical stimulation must be done each 2 mm of resected tumor near eloquent areas.

Regions considered with positive stimulation are those where a disruption during the performance of the task is observed during the stimulation. Those regions will be identified by using a kind of marker. The positive region covered approximately 1 cm2 around the position of the tip of the stimulator.

Apart from the direct stimulation, in most of the centers that awake surgeries with direct stimulation are performed, electrocorticography is usually performed for the detection of after-discharge potentials, which are a subclinical indicator of epileptic activity.

During brain mapping, we do not usually use mannitol or hypertonic saline to avoid brain shift and changes in the elastance of the brain that may influence the results of mapping or make the dissection of the lesion more difficult. Furthermore, if subarachnoid dissections must be done, we perform it once the lesion is functionally disconnected from subcortical pathways because the excessive release of cephalo-spinal fluid may also influence the results of mapping.

#### **5.4 Concomitant use of other tools to maximize the degree of resection**

Brain mapping during an awake procedure can also be combined with other techniques or tools that are useful in brain tumor resection. Image-guided surgery, using neuronavigation or real-time imaging systems (intraoperative MRI or ultrasound), is perfectly compatible with awake surgery. On the other hand, the use of fluorescent compounds (5 aminolevulinic acid, fluorescein, or indocyanine green), which allows to identify the areas of tumor invasion or regions where the blood-brain barrier is disrupted, can also be used during awake surgeries. In any case, the limitations of the resection will always be defined by the functional boundaries established by the direct cortical and subcortical stimulation during task performance.

#### **5.5 Continuous evaluation of patient's feedback**

It is essential to maintain continuous communication with the patient during the surgery. The key to succeeding in an awake surgery lies in adequate preparation of the patient; adequate control of sedation levels; the correct use of analgesia; and ensuring a comfortable position for the patient. Therefore, continuous monitoring of all these aspects contributes to achieve good results in awake surgery for brain tumor.
