*4.1.1 Asleep-awake-asleep*

It consists of general anesthesia in the initial phase, waking up the patient during stimulation/mapping and subsequently, reintroducing general anesthesia for closure. During the general anesthesia phase, the ideal is to achieve airway control with a laryngeal mask (it offers advantages over the placement of a tracheal tube as it is easier to place, avoids head extension, and associates less risk of coughing with vomiting).

Generally, this anesthetic modality is achieved with the use of propofol and remifentanil, since they are short-acting drugs and allow sedation with rapid awakening (5–20 min). The great advantage of propofol is its rapid recovery and a titratable sedative effect, which helps to avoid excessive and unnecessary sedation, but also reduces intracranial pressure and has anti-seizure and anti-emetic properties [19]. In the case of propofol, the infusion should be stopped 15 minutes before the onset of cortical stimulation in adults, 20 minutes before in children [2], and should be restarted for dura closure. It is usually given in combination with a low dose of remifentanil.

The advantages of this modality are better airway control and adequate deep sedation with greater comfort for the patient in the initial phases. In fact, this is the modality that best adjusts to prolonged procedures (>5 h). However, the drawbacks include the complexity involved in repositioning the device in the airway for closure and that general anesthesia increases the risk of hypoventilation, nausea, and agitation during brain mapping [2, 20].

#### *4.1.2 Conscious sedation*

It consists of the administration of sedation during the first stage of the awake craniotomy without airway control (patient breathes spontaneously) [20]. A combination of propofol and remifentanil has been the standard for sedation, but it has been associated with a higher risk of respiratory depression. Dexmedetomidine, a selective alpha2 agonist with sedative, anxiolytic, analgesic, and opioid-sparing properties, has recently been shown to provide easily reversible sedation without associated ventilation depression risk [21]. Likewise, compared with the propofolremifentanil combination, it reduces the incidence of vomiting and coughing, increasing patient comfort during surgery, and facilitating surgical resection by reducing cerebral blood flow [2]. The advantages and disadvantages of this anesthetic modality are registered in **Table 1**.


#### **Table 1.**

*Advantages and disadvantages of each anesthetic modality for awake brain surgery.*

### *4.1.3 Awake*

This modality is the least commonly used. It consists of using local anesthesia and avoiding sedation in any of the stages of surgery with the idea of avoiding the inconveniences of general anesthesia/sedation. It raises the option of avoiding pain, through the infiltration of the scalp and selective blocking of the trigeminal sensory branches [2]. In addition to reducing postoperative pain, it has the great advantage of being able to optimize patient position and improve considerably communication with the patient by avoiding sedative medication [20, 22]. In these cases, some protocols propose the use of hypnosis to produce a dissociative state [23, 24]. The advantages and disadvantages of this anesthetic modality are registered in **Table 1**.

#### **4.2 Anesthetic monitoring during the procedure. Complications**

Premedication is not standardized. Corticosteroids are often used to reduce the mass effect of the tumor lesion and nausea. The risk of seizures is higher than standard surgery due to DCS; thus, anticonvulsant therapy is also usually administered prophylactically, although there is not enough literature evidence to support this indication.

In addition to premedication, it is essential to carry out rigorous anesthetic monitoring during the procedure. This monitoring should include electrocardiogram, invasive blood pressure measurement, pulse oximetry, respiratory rate, capnography, temperature, urinary catheterization, and BIS encephalographic recording.

Although it is usually a safe procedure in experienced professionals, some intraoperative complications related to the anesthetic procedure may occur: seizures (3–30%), high blood pressure (17–24%), desaturation/hypoventilation (7–16%), nausea and vomiting (0–9%), and brain swelling (7–14%) [25]. However, the conversion to a general anesthesia procedure only occurs in less than 2% of surgeries and there is no relationship between failure rate and the type of anesthetic modality [26].
