EDUCATION CORNER

---

Challenging Case: Anesthesia for Awake Craniotomy in an Intraoperative MRI Suite: Clinical Decision-Making and Dilemmas

Deepali Garg*, MD; Sonal Patel, MD; Shobana Rajan, MD
Cleveland Clinic Foundation
*Corresponding author

Shobana Rajan, MD

Deepali Garg, MD

Introduction
Anesthesia for awake craniotomy is a unique clinical setting, with the primary goal of enabling tailored resection of brain lesion near eloquent cerebral cortex, and theoretically maximizing the extent of tumor resection and minimizing the risk for neurological injury. A combination of awake craniotomy and intraoperative MRI (iMRI) requires close collaboration of surgeons, anesthesiologists, technicians and patient. Intraoperative MRI is shown to increase the survival times significantly.¹

The role of the anesthesiologist is crucial both preoperatively, when it comes to determine if each single patient is a suitable candidate for this stressful procedure, and intraoperatively, with regards of maintaining an appropriate level of anesthesia and analgesia compatible with patient being able to talk and follow commands.

We discuss the decision-making process involved in the care of 60-year-old female posted for awake craniotomy with iMRI for brain tumor resection.

We obtained written HIPAA authorization from the patient for submission of the clinical case report for potential publication.

Case Description
A 60-year-old left-handed female was scheduled for awake right frontal craniotomy for a right frontal brain tumor secondary to metastasis. She presented with left side facial droop, left sided weakness, speech difficulty and left facial twitching. Her past medical history was significant for diabetes mellitus, obstructive sleep apnea, Nonalcoholic steatohepatitis, history of pulmonary embolism and obesity (BMI-45). Her medications included: levetiracetam, dexamethasone, enoxaparin and insulin. Patient’s routine preoperative check was unremarkable with all investigations within normal limits. Functional MRI showed bilateral speech dominance for both receptive as well as expressive components of speech, hence the decision was made to perform the tumor resection with neurophysiologic mapping and testing. Airway evaluation showed Mallampati grade two with adequate mouth opening and neck circumference 51cm. Preoperative vitals were within normal limits.

The plan was asleep-awake-asleep anesthesia technique. Monitoring included electrocardiogram, pulse oximetry and a radial arterial line for continuous recording of arterial blood pressure. Oxygen was provided using nasal cannula at a flow of 4L/hr and nasal trumpet was inserted to prevent tongue fall and obstructed airway, given patient’s history of OSA. Conscious sedation was achieved with propofol and dexmedetomidine infusion following which right frontal craniotomy was performed and once the brain was exposed, cortical stimulation was used to localize motor cortex. Tumor debulking proceeded uneventfully while testing the patient in the performance of requested motor and speech tasks. When the operating surgeon estimated that gross total resection of tumor had occurred, sedation was deepened again, LMA inserted and MRI scan obtained. Scan suggested a gross total resection and no further removal was pursued. Post closure of craniotomy incision, LMA was removed and patient was moved to post anesthesia care unit (PACU). Post-operative neurologic assessment showed no change from baseline.

Discussion
This case presented multiple clinical questions and dilemmas to the care team involved:

1. What technique of anesthesia should be employed for this awake craniotomy under intraoperative MRI guidance?
2. What should be the options for airway management in MRI suite?
3. What medications can be used to maintain various stages of sedation required, allowing for uninterrupted tumor resection as well as neurophysiologic testing?
4. What challenges are specific to surgery being performed in MRI suite?
5. What should be done in case of an intraoperative seizure?

Technique of Anesthesia
Many techniques are employed to provide anesthesia and to facilitate neurophysiologic mapping for awake craniotomy, depending on institution’s protocols or patient needs. Two commonly used techniques are monitored anesthesia care (MAC) i.e. local anesthesia with conscious sedation and asleep-awake-asleep anesthesia. Local anesthesia is given by scalp block in combination with pin site infiltration. The local anesthetic drugs frequently used include bupivacaine, ropivacaine and lignocaine, with or without epinephrine. However general anesthesia may be needed in some special scenarios.

We used asleep-awake-asleep technique for our patient as it provides better comfort for the patient and surgical team during the pre-awake phase, reliable protection of patient from painful sensations, hypoventilation, intraoperative movements and airway emergencies. It is also easier to hyperventilate the patient in case of brain swelling.

Airway Management in the MRI suite
To manage the airway of awake non-intubated patients it is essential to ensure adequate oxygen supply, carbon dioxide removal and prevent aspiration. Raised carbon dioxide can have dangerous effects on cerebral blood flow and extracellular pH. Khu et al. in their study showed that patients undergoing tumor removal with awake anesthesia required a larger craniotomy than those receiving general anesthesia, owing to increased brain swelling and compression on the craniotomy edges partly related to higher PaCO2 levels.²

In patients undergoing awake craniotomy, various airway devices can be used, such as nasal cannula or face mask with or without oral/ nasopharyngeal airway, laryngeal mask airway (LMA), endotracheal intubation or fiberoptic guided endotracheal intubation. The LMA is particularly useful for the ‘asleep-awake-asleep’ craniotomies because of the ease of insertion, reliable airway protection and better control of end-tidal carbon dioxide. It also has the advantage of being inserted without the use of laryngoscope or head extension and is associated with a lower incidence of coughing and gagging.³ Our patients are usually on pins when we insert LMA just before MRI scanning, therefore insertion is done in head turned towards one side with no possibility of neck movement, making LMA the preferred choice. LMA can also be used to provide CPAP in morbidly obese patients breathing spontaneously. Huncke et al. described the successful use of an LMA along with continuous positive-pressure ventilation in a morbidly obese patient with obstructive sleep apnea undergoing awake craniotomy.⁴

Anesthetic Agents
Various medications can be used to maintain sedation during the asleep phase of awake craniotomy. Commonly used drugs are propofol, dexmedetomidine, remifentanil and inhalational agents.

Propofol is used as an infusion with dose ranging from 25-75mcg/kg/min. It has a context-sensitive half-life of 40mins even for prolonged infusions. However, it can be associated with dose-dependent respiratory depression with a risk of hypercapnia and subsequent brain swelling. Hence, in this approach, precise dosing of propofol is the key.

Dexmedetomidine is a centrally acting alpha agonist that has sedative and analgesic properties without causing respiratory depression. It provides a sedated, yet cooperative patient.

More recently, a combination of remifentanil and propofol has been used successfully.⁵ Remifentanil’s context-sensitive half-life is short (<5 minutes) and independent of infusion duration, which allows a rapid modulation of analgesia and sedation required during the course of the surgery.

Traditional halogenated inhalational anesthetics like sevoflurane, desflurane can also be used for maintenance of anesthesia during awake craniotomy. However, they are not an ideal choice due to their potential for causing elevation of intracranial pressure and a higher risk of nausea and vomiting upon intraoperative emergence.

Challenges in the iMRI Suite
Intraoperative MRI adds an extra layer of complexity to an already demanding anesthetic management in awake craniotomy. Anesthesia in an iMRI setting can be challenging due to various reasons: high level acoustic noise adding to patient anxiety, remote location of the iMRI suite, additional anesthesia help may not be readily available in emergency situations such as management of a difficult airway, risk of ferromagnetic projectiles causing injury, requirement of longer extension tubing for fluids and infusions and availability of staff trained to work in an MRI environment. Also, anesthesia needs to be maintained with MRI-compatible equipment including MRI-compatible monitoring, airway equipment, anesthesia machine, intravenous fluid connectors, medication pumps and so forth.⁶ The commercially available MRI-compatible monitors do not allow for ST segment monitoring, and electrical noise generated during the MRI scan can distort or completely mask the electrocardiogram waveform. During the scan, the patient is at risk for thermal injury from any monitoring cables that can potentially induce a current from the magnetic field. It is important to buffer all skin-to-skin and skin-to-cable contact with adequate padding to prevent thermal injury.⁷

Intraoperative Seizures
According to the latest survey of European clinics which retrospectively collected data from 823 cases of intraoperative brain mapping, the frequency of seizures during awake craniotomy varies widely from 2.9 to 54%.⁸ The leading risk factor is a history of preoperative seizures. Irrigation of the brain tissue with ice cold crystalloid solution could stop a seizure or prevent its generalization in a timely manner. In case of inefficacy of irrigation, bolus of propofol or benzodiazepine can be administered. Antiepileptics might be needed in case of status epilepticus.

Conclusion
Combination of awake craniotomy and intraoperative MRI is demanding and necessitates extensive preparation by the entire team. Careful preoperative evaluation is essential to ensure patient compliance. The presence of a magnetic field, as well as reduced access to the patient during the MRI scan, require high levels of attentiveness. Specialized, MRI-compatible equipment is required for this environment, and providers should be familiar with this equipment and its limitations. The use of checklists and teamwork training can maximize both patient and provider safety in the intraoperative MRI environment.

References

1. Wirtz CR, Knauth M, Staubert A, Bonsanto MM, Sartor K, Kunze S, et al. Clinical Evaluation and Follow-up Results for Intraoperative Magnetic Resonance Imaging in Neurosurgery. Neurosurgery. 2000 May 1;46(5):1112–22.
2. Khu KJ, Ng WH. Intraoperative swelling leading to neurological deterioration: an argument for large craniotomy in awake surgery for glioma resection. J Clin Neurosci. 2009;16(7):886–8.
3. Sarang A, Dinsmore J. Anaesthesia for awake craniotomy—evolution of a technique that facilitates awake neurological testing. Br J Anaesth. 2003;90(2):161–5.
4. Huncke T, Chan J, Doyle W, Kim J, Bekker A. The use of continuous positive airway pressure during an awake craniotomy in a patient with obstructive sleep apnea. J Clin Anesth. 2008;20(4):297–9.
5. Johnson KB, Egan TD. Remifentanil and propofol combination for awake craniotomy: case report with pharmacokinetic simulations. J Neurosurg Anesthesiol. 1998;10(1):25–9.
6. Ehrenwerth J, Singleton M, Jose S. American Society of Anesthesiologists Task Force on Anesthetic Care for Magnetic Resonance Imaging. Practice advisory on anesthetic care for magnetic resonance imaging: a report by the Society of Anesthesiologists Task Force on Anesthetic Care for Magnetic Resonance Imaging. Anesthesiology. 2009;110:459–79.
7. Anesthetic management and human factors in the intraoperative MRI environment | Ovid [Internet]. [cited 2018 Nov 14]. Available from: https://oce-ovid-com.ccmain.ohionet.org/article/00001503-201610000-00007/HTML
8. Spena G, Schucht P, Seidel K, Rutten G-J, Freyschlag CF, D’Agata F, et al. Brain tumors in eloquent areas: A European multicenter survey of intraoperative mapping techniques, intraoperative seizures occurrence, and antiepileptic drug prophylaxis. Neurosurg Rev. 2017;40(2):287–98.