Anesthesia for Awake Craniotomy in a Patient With History of Malignant Hyperthermia: Clinical Dedision Making and Dilemmas
By Sonal Patel, MD
Deepali Garg, MD
Marco Maurtua, MD
Shobana Rajan, MD
Cleveland Clinic Foundation
Contribution by Trainee Engagement Committee of SNACC
|Shobana Rajan, MD|
|Deepali Garg, MD|
Malignant hyperthermia-susceptible patients have an increased risk during anesthesia. MH events are associated with significant morbidity rates that range from 20 to 35 %.2, 3, 4 For each 10-min delay in administration of dantrolene, complications increase substantially. If dantrolene administration is delayed beyond 50 min, complication rates increase to 100 %.5 MH–related complications include neurologic, cardiac, renal, and hepatic dysfunction, pulmonary edema, disseminated intravascular coagulation, and compartment syndrome.3 A recent North American MH Registry of MHAUS study reports mortality rates as high as 9.5%.4
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 to maximize the extent of tumor resection and minimize the risk for neurological injury. It requires close collaboration of surgeons, anesthesiologists, technicians and patient.
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 to maintaining an appropriate level of anesthesia and analgesia compatible with the patient being able to talk and follow commands.
We discuss the decision-making process involved in the care of a 42-year-old male with a history of MH posted for awake craniotomy for brain tumor resection.
We obtained written HIPAA authorization from the patient for submission of the clinical case report for potential publication.
A 42-year-old right-handed male with a history of malignant hyperthermia was scheduled for awake right-sided craniotomy for a right frontoparietal tumor. He presented with one week of fatigue, left side facial droop, left hand numbness and bilateral leg weakness. His past medical history was significant for malignant hyperthermia that occurred when he underwent tonsillectomy at the age of seven years. He was kept under observation and did well at that time. He later had muscle biopsy that confirmed the diagnosis of malignant hyperthermia.
Patient’s routine preoperative check was unremarkable with all investigations within normal limits. Airway evaluation showed Mallampati grade 2 with adequate mouth opening and full range of neck movements. Preoperative vitals were within normal limits. His medications included Dexamethasone 4mg QDS and Keppra 500mg BiD.
MRI brain demonstrates R frontoparietal rim-enhancing lesion that appeared to be originating in post central gyrus, displacing motor cortex anteriorly. Hence the decision was made to perform the tumor resection with motor mapping and SEPs testing.
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.
Complete cleaning of anesthesia workstation was done and new circuit washed in the lab with 100% oxygen for 20 minutes was installed to avoid any triggers for MH. The inhalation agent was removed from the anesthesia machine and was taped to ensure that there is no accidental insertion of the vaporizer.
Oxygen was provided using MAC safe nasal cannula at a flow of 4L/min and nasal trumpet was inserted to prevent tongue fall and obstructed airway. Sedation was achieved with propofol and dexmedetomidine infusion following which right craniotomy was performed and once the brain was exposed, infusions were stopped to wake up the patient for the cortical stimulation to localize motor cortex. Tumor excision proceeded uneventfully while testing the patient in the performance of requested motor and speech tasks. When the operating surgeon estimated that the resection of tumor had occurred, sedation was restarted again. Post closure of craniotomy incision, patient was moved to post anesthesia care unit (PACU). Post-operative neurologic assessment showed no change from baseline.
This case presented multiple clinical questions and dilemmas to the care team involved:
- What are the safety precautions to avoid MH crisis?
- What technique of anesthesia should be employed for this awake craniotomy?
- What should be the options for airway management in case of obstruction/loss while avoiding MH triggers?
- What medications can be used to maintain various stages of sedation required, allowing for uninterrupted tumor resection as well as neurophysiologic testing and ensuring to avoid triggering MH?
- How to manage an intraoperative MH crisis?
- How long should MH patients be monitored after uneventful anesthesia?
It is very important to have a clear and effective communication between the entire OR team with anesthesiologist being the leader in case of uneventful MH crisis. The anesthesia machine requires preparation.
The vaporizers should be disabled from the machine, flush the machine with a fresh gas flow rate more than 10 l/min using the ventilator for at least 20 minutes (picture 1).10 However, depending on the make and model of the machine, the requirements may vary. Hence we called the engineers for preparation and they changed the whole ventilatory system and replaced it with clean system run through 100% oxygen in their lab for 20 minutes (see picture 2). Replacement of the fresh gas outlet hose, carbon dioxide absorbent, and anesthesia circuit 10 with fresh new one is essential
|Ventilatory Circuit from Lab
We also kept the MH cart (picture 3) in OR and made sure it had adequate dantrolene and proper instructions for its constitution if needed.
The two most commonly used techniques for awake craniotomy are monitored anesthesia care (MAC), i.e. local anesthesia with conscious sedation and asleep-awake-asleep anesthesia. In this case with MH, the safe technique is local anesthesia with sedation achieved with propofol, dexmedetomidine, and opioids totally avoiding the use of inhalation agents and succinylcholine. 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.
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 and intraoperative movements totally avoiding any triggers for MH.
Airway Management in Case of Obstruction:
In order to manage the airway of awake non-intubated patients, it is essential to ensure adequate oxygen supply, carbon dioxide removal and to 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.6 Various airway devices such as nasal cannula, Mac safe nasal cannula, face mask with or without oral/ nasopharyngeal airway, laryngeal mask airway (LMA), endotracheal intubation or fiberoptic guided endotracheal intubation can be used. 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.7
Various medications can be used to maintain sedation during the asleep phase of awake craniotomy. Commonly used drugs are propofol, dexmedetomidine and remifentanil.
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.8 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, in this case all inhalational agents were contraindicated.
Management of MH Crisis:
The incidence of malignant hyperthermia is low, but the prevalence can be estimated as up to 1: 3000.
The most important medication is dantrolene. It is diphenylhydantoin and it decreases calcium-induced calcium release from SR. It is started at dose of 2.5mg/kg iv every 30 min till the symptoms resolve (maximum dose 10mg/kg) and then continue 1mg/kg iv every six hours for 24 hours.
For each 10-min delay in administration of dantrolene, complications increase substantially. If dantrolene administration is delayed beyond 50 min, complication rates increase to 100 %.1
The new formulation of Dantrolene known as Ryanodex is much easier for administration. It does not require dissolution in large amounts of distilled water, instead one 5cc vial powder provides a sufficient dose for a 70-80 kg adult patient and this significantly reduces the preparation and administration time.
According to the Malignant Hyperthermia Association of United States, the guidelines are summarized in the MH card (picture 4).
Monitoring After Uneventful Anesthesia:
The patient susceptible to MH undergoing outpatient surgery may be discharged on the day of surgery if the anesthetic has been uneventful. A minimum period of 1.0 hour in PACU monitoring vital signs at least every 15 minutes and an additional hour in phase 2 PACU /step down unit is recommended.9
Awake craniotomy in a patient with history of MH is very demanding and requires extensive preparation by the entire team. Careful preoperative evaluation is essential to ensure patient compliance and teamwork is crucial to avoid preventable MH events.2
The incidence of malignant hyperthermia is low, but the prevalence can be estimated as up to 1: 3000. Because malignant hyperthermia is potentially lethal, it is relevant to establish management concepts for perioperative care in susceptible patients.
Preparation of the anesthetic workstation, use of non-triggering anesthetics, adequate monitoring, availability of sufficient quantities of dantrolene and appropriate postoperative care - taking these items into account, anesthesia can be safely performed in susceptible patients.
- Curr Opin Anaesthesiol. 2010 Jun; 23(3) Anesthesia for patients with a history of malignant hyperthermia.
- Riazi, S, Kraeva, N, Hopkins, PM Malignant hyperthermia in the post-genomics era: New perspectives on an old concept. Anesthesiology 2018; 128:168–8.
- Larach, MG, Gronert, GA, Allen, GC, Brandom, BW, Lehman, EB Clinical presentation, treatment, and complications of malignant hyperthermia in North America from 1987 to 2006. Anesth Analg 2010; 110:498–507 [Article] [PubMed].
- Larach, MG, Brandom, BW, Allen, GC, Gronert, GA, Lehman, EB Malignant hyperthermia deaths related to inadequate temperature monitoring, 2007–2012: A report from the North American Malignant Hyperthermia Registry of the Malignant Hyperthermia Association of the United States. Anesth Analg 2014; 119:1359–66 [Article] [PubMed].
- Riazi, S, Larach, MG, Hu, C, Wijeysundera, D, Massey, C, Kraeva, N Malignant hyperthermia in Canada: Characteristics of index anesthetics in 129 malignant hyperthermia susceptible probands. Anesth Analg 2014; 118:381–7 [Article] [PubMed].
- 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.
- 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.
- Johnson KB, Egan TD. Remifentanil and propofol combination for awake craniotomy: case report with pharmacokinetic simulations. J Neurosurg Anesthesiol. 1998; 10(1):25–9.
- Malignant Hyperthermia Association of the United States - 2019.
- Tae W. Kim, M.D.; Michael E. Nemergut, M.D., Ph.D. Anesthesiology 1 2011, Vol.114, 205-212.