9.1 Introduction

An awake craniotomy can facilitate more effective surgery especially when a lesion is located in eloquent brain regions such as the motor or language cortical and subcortical areas. ^{1 ,​ 2 ,​ 3 ,​ 4 ,​ 5 ,​ 6 ,​ 7 ,​ 8 ,​ 9 ,​ 10 ,​ 11 ,​ 12 ,​ 13 ,​ 14 ,​ 15 ,​ 16 ,​ 17 ,​ 18 ,​ 19 ,​ 20 ,​ 21 ,​ 22 ,​ 23 ,​ 24 ,​ 25 ,​ 26 ,​ 27 ,​ 28 ,​ 29 ,​ 30 ,​ 31 ,​ 32 ,​ 33 ,​ 34 ,​ 35 ,​ 36 ,​ 37 ,​ 38 ,​ 39 ,​ 40 ,​ 41} It has also been advocated for cortical and subcortical regions that were historically considered noneloquent, but now has been shown to be important for functions such as decision making and facial recognition. During surgery, patients are asked to perform tasks to map important functional regions in the brain. Effective mapping is paramount to maximizing resection while minimizing the risk of iatrogenic deficits. ^{12 ,​ 13 ,​ 14 ,​ 18 ,​ 20 ,​ 21 ,​ 22 ,​ 23 ,​ 24 ,​ 25 ,​ 42} In brain tumor cases through greater extent of resection (EOR), awake craniotomies can improve length of survival while maintaining or increasing quality of life for patients. ^{12 ,​ 13 ,​ 14 ,​ 18 ,​ 20 ,​ 21 ,​ 22 ,​ 23 ,​ 24 ,​ 25 ,​ 42} While brain stimulation is performed for functional mapping of cortical and subcortical structures, when combined with an awake craniotomy, surgeons are able to create a more thorough and accurate map of eloquent cortical and subcortical regions. ^{3 ,​ 4 ,​ 12 ,​ 13 ,​ 14 ,​ 19 ,​ 24 ,​ 28 ,​ 29 ,​ 30}

Awake craniotomies vary slightly from normal neurosurgical cases. From a neuroanesthesia perspective, medications must be carefully titrated throughout the procedure to allow for patient comfort, without reducing the patient’s ability to cooperate with their tasks. In terms of operating room (OR) setup, the patient must be positioned and draped correctly to perform and visualize intraoperative tasks. Finally, awake craniotomies require additional equipment, personnel, and supplies. The goal of this chapter is to review basic OR setup for awake craniotomies with brain mapping including patient positioning, intraoperative imaging, and neuronavigation.

9.2 Awake Craniotomy Operating Room Setup

Surgical efficiency can be improved through correct OR layout including positioning of the patient and anesthesia, navigation equipment, and critical and noncritical personnel ( Fig. 9‑1 ). Most ORs have an operating table in the center of the OR that should be adjusted for correct patient positioning and for surgeon preference (see section “Patient Positioning” for more details). ³⁹ Within the sterile field and opposite the door to the OR, there should be a Mayo stand and a back/scrub table ( Fig. 9‑1 ). Due to its mobility, a Mayo stand provides increased accessibility to necessary equipment throughout the procedure. The height and location of the Mayo stand will be adjusted according to patient positioning and surgeon preference.

Direct visualization of the patient’s face is required during the procedure. An unobstructed, preferably transparent tent is made with the sterile surgical drape to allow for the visualization of not only the patient’s face but also the patient’s arms and legs as needed for monitoring ( Fig. 9‑1, Fig. 9‑2). By creating the tent, it also minimizes the patient’s potential for anxiety from claustrophobia. Consoles for surgical equipment such as mono- and bipolar coagulation units, drills, and suction containers and electrophysiological monitoring machines are located at the foot of the operating table to reduce wire tangling and obstruction of the sterile field. ^{39 ,​ 43} The OR microscope and chair should be draped and positioned at the head of the operating table, ready for use when required. There should be multiple monitors placed throughout the OR for use by surgeons, OR personnel, and anesthesiologists; these can be used by nonsurgical staff, including students, for observation. During surgery, these allow the surgeon to view the patient’s face and limbs and navigational imaging, which helps the surgeon to dynamically adjust the approach. ^{39 ,​ 40 ,​ 43}

In awake neurosurgical cases, primary surgeon, assistant surgeon, a scrub technician, a circulating nurse, anesthesiologist, and an examiner (preferably a qualified neurologist or neuropsychologist) are required. At academic centers, a neurosurgery resident, an anesthesia resident, certified registered nurse anesthetist (CRNA), and/or medical and undergraduate students are generally available in the OR. Additionally, an electrophysiological technician may be present when neurophysiological monitoring is required. Given the ease with which the OR can become crowded, an optimal OR setup is necessary to maintain the flow and efficiency during the operation. It is also important to keep the number of personnel and the noise level to a minimum as the patient is awake, and the surgeon must be able to hear and examine the patient carefully at all times.

The lead surgeon will be at the head of the OR table with the scrub technician on the patient side within arm’s reach of the Mayo stand, back/scrub table, and the surgeon and typically opposite to the side of the patient being evaluated (Fig. 9‑1). The anesthesiologist will be positioned on the contralateral side from the site of surgery and near the head and chest area of the patient. This allows for access to all anesthesia equipment, the endotracheal tube, and the intravenous/intra-arterial lines. The anesthesia machines should be placed close to the head of the OR table (Fig. 9‑1). The examiner (neurologist or neuropsychologist) will be positioned in front of the patient with a clear view of the face, arm, and legs. To ensure a proper place for the examiner, all monitoring machines should be placed far away from the patient ( Fig. 9‑1 ).

It should be noted that an alternative is to position the patient 180 degrees away from the anesthesia machine. This setup has been preferred by several surgeons, as it increases the working space around the patient’s head. However, the disadvantage is that the patient’s airway is further away from the anesthesia machine, which can make it difficult to access during emergency situations.

9.3 Awake Anesthesia

There are two main anesthetic techniques for awake craniotomies: monitored anesthesia care (MAC) and “asleep, awake, asleep” (AAA). ^{7 ,​ 15 ,​ 16 ,​ 17 ,​ 26 ,​ 27} During MAC, the patient is kept in a state of conscious sedation. ⁷ The AAA method, on the other hand, uses a partial or fully protected airway often with a laryngeal mask airway (LMA). ^{7 ,​ 15 ,​ 16 ,​ 17 ,​ 26 ,​ 27} There is a paucity of literature and class I data highlighting the superiority of either technique over the other.

At our institution, patients receive a complete scalp block to the bilateral supraorbital, pre- and postauricular, and lesser and greater occipital nerves, as well as supplementation to the pin sites with lidocaine and/or bupivacaine in the preoperative holding area. An alternative for more precision is to use high-frequency ultrasound to identify the nerves for blocking. Intravenous anesthetics should be chosen with the following criteria: short acting, fast onset and offset, amnesia and adequate pain management, and easy to titrate. ⁷ The decision for pursuing either anesthetic technique should be taken to determine the anesthetic phases and agents before and after cortical mapping. Supporters of the AAA technique advocate that the first phase should include general anesthesia with LMA for positive ventilation, due to low risk of hypertension and/or excessive use of sedation. ^{44 ,​ 45} In this phase, the combination of remifentanil and propofol is preferred as it provides adequate ventilation and rapid transition to awakening. MAC technique, on the other hand, aims to utilize a combination of rapid-onset and short-acting sedative analgesics with high therapeutic index and low risk for cardiorespiratory depression. ⁴⁶ Several sedative agents have been used for the MAC technique, such as droperidol/alfentanil, ⁴⁷ propofol-fentanyl, ⁴⁸ propofol-remifentanil, ⁴⁹ and dexmedetomidine. ^{50 ,​ 51 ,​ 52} The anticipated surgical duration plays a crucial role in the selection of the technique of choice. In a previous study by Lobo et al, ⁴⁶ it was suggested that AAA technique should be used in surgeries with durations exceeding 4 hours, as patients tend to cooperate better in longer surgeries by minimizing their awake time. The type of anesthesia technique also depends on the type of mapping being done. For more intricate mapping including phonetics, semantics, and nonverbal semantics, AAA technique is preferred because patient fatigue can interfere with precise examination. The MAC technique can be done when less precise mapping is needed, such as when language output and motor/somatosensory function are being mapped. Regardless, Eseonu et al documented that there was no difference between MAC and AAA techniques as both provide safe and efficient anesthetic techniques. ⁷

Awake craniotomy has gained popularity for the neurosurgical treatment for gliomas and epilepsy and tends to be very well tolerated. ¹⁶ However, anxiety is a commonly associated response to any surgical intervention, ⁵³ but the concept of being consciously awake during brain surgery in particular can be fraught with a range of fear and anxieties. ^{54 ,​ 55} Sounds and scenes from the OR are known as stressors for patients, which can be the leading cause of anxiety. ⁵⁶ Literature has revealed that there is a consistent relation between intraoperative surgical anxieties and postoperative pain, ^{57 ,​ 58} which leads to increase in analgesic needs ⁵⁹ and delayed recovery. ⁶⁰ A previous study by Legrain et al ⁶¹ hypothesized that pain perception could be interrupted by applying attention-grapping stimuli for distraction. Thus, the utilization of music, ⁶² comforting words, ⁶³ audiovisual stimuli, and touch has shown to be effective in the reduction of pain and anxiety before and during the surgical procedure. Therefore, our surgical team is partnering with the Mayo Clinic Robert D. and Patricia E. Kern Center for the Science of Health Care Delivery to conduct several studies exploring the role of music in improving patient experience in the OR during awake craniotomies.