Anesthesia for Awake Craniotomy

Indications

1. The most common surgical indication for awake craniotomy is resection of the tumor in the vitally important area of the brain like the motor cortex located in the prefrontal gyrus (Brodmann area 4), the sensory cortex located in the postcentral gyrus (Brodmann areas 3,1,2), and language cortex (Broca’s and Wernicke’s area). The awake patient can provide invaluable inputs, which help delineate the patient's functional brain topography and thus help the surgeon know to what extent the tumor can be excised while minimizing the risk of neurological injury to this vital area of the brain.
2. Awake craniotomy is used to facilitate electrocorticography for seizure focus localization and resection as it minimizes interference from anesthetic medications.
3. Awake craniotomy is also used for deep brain stimulation surgery classically for Parkinson disease and other central movement disorders, Alzheimer disease, and psychiatric disease.
4. It is also commonly used for stereotactic brain biopsy and ventriculostomy.
5. Awake craniotomy is also used in interventional pain procedures such as pallidotomy and thalamotomy.

Benefits of Awake Craniotomy

The most important benefit of awake craniotomy is that it allows the neurosurgeon to maximizes tumor resection while preserving neurological function.  Other benefits of awake craniotomy include: 

• Reduced need of monitoring in ICU after surgery and thus shorter or eliminated intensive care unit (ICU) stay.[5][6]
• Patients undergoing awake craniotomy have fewer neurological deficits (7% vs. 23%) and shorter hospital stays (1.7 vs. 9 days) than patients undergoing craniotomy under general anesthesia.[7]
• Patients undergoing awake craniotomy under sedation do not need general anesthesia and avoid the risk inherent to general anesthesia, intubation, and mechanical ventilation.
• Postoperative pain, nausea, and vomiting are also reduced in awake craniotomy compared with the craniotomy under general anesthesia.[8]

Contraindications

Patient refusal and inability to co-operate and obey commands are absolute contra-indications for awake craniotomy. Patient cooperation is necessary to evaluate their language, memory, and motor skills.

Relative contra-indications of awake craniotomy include obese patients, patients with a history of obstructive sleep apnea, difficult airways, and patients with chronic cough. Resection resulting in large blood loss is also not done under an awake craniotomy.

Preparation

Pre-op Evaluation

Well-motivated and mature patients who can tolerate lying still for several hours and cooperate during testing are the best candidates for awake craniotomy. The procedure should be explained to the patient so that he feels comfortable during the intra-operative period. The anesthesiologist should discuss the rationale for awake craniotomy, steps of the procedure, expected degree of pain and discomfort, tasks required for testing, and the possibility of adverse events. Patients undergoing awake craniotomy should be prepared psychologically in addition to medical optimization.

Premedication for craniotomy should be individualized based on the patient's level of anxiety, baseline neurologic status, comorbidities, and the anesthesia plan. Patients having seizure mapping should not receive benzodiazepines or any medications that suppress epileptiform activity. Patients must take their usual steroid, anti-epileptic, or anti-hypertensive medications.

Monitoring

Standard ASA monitors, including electrocardiogram, pulse oximeter, non-invasive BP, ETCO2 monitor, and temperature monitors, are used. The intra-arterial line is frequently used for beat-to-beat BP monitoring and ABG analysis.  Central venous catheterization may be done for infusion of fluids and vasoactive agents. For craniotomy in a sitting position, precordial Doppler helps detect venous air embolism. Monitors should be placed on the same side as brain lesions to avoid interfering with contralateral sensorimotor monitoring. A processed EEG monitor (bispectral index ) may be used to regulate the dose of anesthetic agents and for rapid awakening for intraoperative language testing.

Technique or Treatment

Anesthesia Technique

 Anesthesia technique varies depending upon the surgeon, pathology, length of surgery, and patient factors. It may be

• Conscious sedation throughout (Awake–awake–awake)
• General anesthesia with an intraoperative awakening for brain mapping.  General anesthesia may be used for both the beginning and the end of the procedure (i.e., asleep-awake-asleep) or only for the beginning (i.e., asleep-awake).

Conscious Sedation (Awake–awake–awake)

Moderate sedation is administered during the initial stimulating portions of the procedure like application of the Mayfield Pins, skin incision, removal of the bone flap.  Sedation is stopped or decreased during cortical mapping and restarted during closure. The goal of sedation is to keep the patient responsive to verbal or tactile stimulation with competent airways (moderate sedation). Excessive sedation may result in airway obstruction, hypotension, respiratory depression, and apnea.

Low-dose propofol (50 to 150 mcg/kg/min) and/or  remifentanil (0.01 to 0.05 mcg/kg/min) infusions titrated to desired effect are an excellent choice for moderate sedation in these patient. Benzodiazepines should be avoided during awake craniotomy that involves electrocorticography.

 Dexmedetomidine, a highly selective α2-adrenergic receptor (α2-AR) agonist, has emerged as a suitable sedative agent for awake craniotomy. It was approved for sedation in 1999 by the Food and Drug Administration (FDA). It is used in dose of 0.5 to 1 mcg/kg IV bolus  followed by infusion of 0.3 to 0.7 mcg/kg/hour.  The primary advantage of Dexmedetomidine is that it does not cause respiratory depression. Also, it does not interfere with electrocorticography like benzodiazepines. However, it may result in hypotension and bradycardia.

 General anesthesia with intraoperative awakening (asleep-awake-asleep technique ): General anesthesia is induced at the start, and the airway is often secured with endotracheal intubation or supraglottic airway device. The patient is kept under General anesthesia during the stimulating part of the surgery, i.e., skull pinning, craniotomy, and dural opening. Once the dura is open, the patient is awakened so that he or she can participate during cortical mapping.

Once the mapping is completed, general anesthesia is induced again. If the airway is secured with endotracheal intubation, the patient may cough or be agitated during the awake phase resulting in brain swelling and interference with surgery. LMA produces less stimulation and a smoother transition from one phase to other and so preferred over endotracheal intubation. However, LMA may get displaced during positioning or intra-op, requiring emergency intubation.

Total intravenous anesthesia using propofol and remifentanil infusion is commonly used. Dexmedetomidine may be used along with propofol. During the sleep phase, rapid-acting inhalation agent like sevoflurane has been used successfully.

Regional Scalp Block

Before pinning the head in Mayfield Pins, a bilateral scalp block is commonly done to provide effective analgesia during awake craniotomy. Scalp block provides hemodynamic stability, decreases the stress response to painful stimuli, and thus makes the procedure tolerable, particularly during the awake phase when cortical mapping is done. The scalp block is performed by infiltrating a local anesthetic to seven nerves on either side of the scalp. These nerves include the supraorbital nerve, supratrochlear nerve, zygomaticotemporal nerve, auriculotemporal nerve, lesser occipital nerve, greater occipital nerve, and greater auricular nerve.

Complications

Challenges/Complication During the Awake Phase

1. Seizures: incidence of seizure is 2% to 20% in awake craniotomy. A seizure occurs most commonly during stimulation for brain mapping. Many intraoperative seizures are focal, brief, and resolve spontaneously, whereas others are generalized. Patients with a history of seizures and younger patients, especially with tumors of the frontal lobe, are more prone to seizures.[9] Intraoperative seizures have a higher incidence of transient motor deterioration and longer hospital stays.[10] First-line treatment should be irrigation of the brain with sterile iced saline. Propofol bolus (10 to 20 mg IV) or midazolam (1 to 2 mg IV) should be administered to terminate the seizure if iced saline is ineffective.
2. Hypertension: Hypertension is commonly secondary to pain, agitation, and anxiety. However, other causes like hypoxia, hypercapnia must be checked. Underlying causes should be taken care of, and Labetalol or esmolol may be administered as a temporizing measure.
3. Nausea and vomiting – Nausea is seen in approximately 4 percent of patients undergoing awake craniotomy. It is usually due to opioids, anxiety, or surgical stimulation. Ondansetron, dexamethasone, and propofol are suitable drugs to manage nausea and vomiting.
4. Respiratory complications: Airway obstruction may occur due to excessive sedation, causing hypoxia and hypercarbia. Oral/ nasopharyngeal airways may relieve airway obstruction but assisted ventilation and a supraglottic intubation device may be needed to manage hypoxia and hypercarbia.
5. Air Embolism: Incidence of venous air embolism is as high as 20 to 40% during craniotomy in sitting position. Transesophageal echocardiography (TEE) is the most sensitive device to detect air embolism.  It can detect as little as 0.02 mL/kg of air, but it is invasive. Precordialdoppler is the most commonly used device for the detection of air embolism.
6. Hyponatremia: Hyponatremia is the most frequent electrolyte imbalance in neurosurgical patients. Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is the most common cause of hyponatremia. Still, other causes like Acute ACTH deficiency or Cerebral salt wasting syndrome (CSWS) should also be considered. SIADH is characterized by inappropriate water retention leading to dilutional hyponatremia in a clinically euvolemic patient, whereas excessive natriuresis resulting in relative hypovolemia is seen in CSWS. Hyponatremia may increase intracranial pressure, delayed awakening, and neurologic deterioration.
7. Failed awake craniotomy: Awake craniotomy was considered a failure if conversion to general anesthesia was required or if adequate mapping or monitoring could not have been achieved. Failed awake craniotomy occurs in about 2 percent (0% to 6%) of awake craniotomies,  may be minimized by appropriate patient selection.[11]

Postoperative Care

After the surgery, the patient is usually transferred to a high dependency unit or ICU. Pain management can be achieved by multi-modal analgesia technique utilizing regional anesthesia technique (scalp block or local infiltration), acetaminophen, small doses of opioids intravenously, including patient-controlled analgesia. Postoperative analgesic requirement and the incidence of nausea and vomiting are lower in awake craniotomy than craniotomy under general anesthesia.

Clinical Significance

Awake craniotomy with brain mapping is the gold standard for resections of tumors or lesions in or near eloquent areas of the brain. Neurological deficits resulting from excision or injury of areas essential for speech and motor control functions might be devastating. The gold standard technique for mapping these vital areas involves direct electrical stimulation of the cortex while the patient is awake. The awake patients will be able to perform a relevant task and thus help determine if the stimulus disrupts the execution of the particular task.

Proper patient selection and patient counseling are of paramount importance. A co-operative patient who can follow commands during surgery is a must for brain mapping; therefore, improper patient selection may result in failure of awake craniotomy. The patient should be told about the details of the procedure and what is expected from them so that they are calm and cooperative during surgery. Judicious use of sedation and neve block is mandatory to keep the patient pain-free, comfortable, and cooperative.

Enhancing Healthcare Team Outcomes

To enhance interprofessional healthcare team outcomes, measures should aim to provide the safest yet effective intervention for the patient. Different improvement strategies aiming to improve patient care and interprofessional team outcomes can be implemented and divided into preoperative, intraoperative, and postoperative.

Pre-operative measures include proper patient selection and patient counseling. Both anesthesiologists and neurosurgeons should talk to the patient before surgery to allay patient concerns and anxiety.

Neurosurgeons, anesthesiologists/nurse anesthetists, and neuromonitoring technicians need to operative as a team, coordinate their activities, and communicate effectively for diagnosis and managing problems promptly. [Level 5]

Nursing, Allied Health, and Interprofessional Team Interventions

Interprofessional team-based practices are vital for a successful awake craniotomy. The anesthesiologist and surgery team should discuss and plan for the procedure before a patient comes to the operating room. Equipment needed for surgery and patient position should be discussed with the operating room nurse. Effective communication between all team members, including the anesthesiologist/nurse anesthetists, surgeon, technician, and nurses, minimizes complications and makes the procedure successful.