Although awake craniotomies are often performed under general anesthesia, they can also be performed safely and effectively using scalp blocks with dexmedetomidine. Surgical conditions using this approach are ‘ideal,’ a Toronto research team argued, simultaneously minimizing the risk for neurologic deficit and maximizing the potential for surgical resection.
According to Niamh A. McAuliffe, MD, a lecturer in anesthesia at the University of Toronto, awake craniotomy has long been the gold standard for tumor resection in eloquent regions of the brain. “Traditionally, this was performed using an asleep-awake-asleep approach with patients induced under general anesthesia for craniotomy and opening of the dura. In more recent times, however, a propofol-remifentanil–based approach for neurolept-anesthesia has been popular. However, this has been associated with respiratory depression rates of up to 14%, which led us to look at dexmedetomidine.”
Dexmedetomidine has been used for awake craniotomy since 2001, and has been described in both general and neurolept techniques, she noted. “The agent has several attractive features for awake craniotomy, including its anxiolytic, sedating and anesthetic properties. It’s been shown to have improved arousal time compared to propofol in recent studies and has also been shown to decrease vascular perfusion, which is attractive for patients with potentially tight brains.”
Retrospective Assessment of Technique
Several years ago, the researchers implemented a standardized anesthetic technique using scalp blocks with dexmedetomidine in patients selected for awake craniotomy because of anatomic characteristics of brain tumor pathology. “Using this protocol, we used a dexmedetomidine-based infusion, supplemented with small doses of midazolam and fentanyl for scalp block, with local infiltration for pinning,” Dr. McAuliffe said. “The infusion is turned off 10 to 15 minutes before testing.”
To determine the safety and efficacy of this technique, the investigators conducted a retrospective cohort study of eligible patients who underwent awake craniotomy at their institution, St. Michael’s Hospital, between 2012 and 2016. They assessed several characteristics of the procedure, including the incidence of critical perioperative airway outcomes, perioperative complications and successful intraoperative mapping.
The study’s primary anesthesia outcome was the incidence of perioperative airway complications, and the primary surgical outcome was the correlation between functional MRI (fMRI) analysis and intraoperative brain mapping, as well as the incidence of altered surgical management due to information acquired during real-time brain mapping.
A total of 55 patients completed the awake craniotomy protocol with successful tumor resection; the median procedure length was 200±50 minutes. As Dr. McAuliffe reported at the 2017 annual meeting of the Canadian Anesthesiologists’ Society (abstract 284705), the technique proved successful on a variety of fronts.
Informative Intraoperative Mapping
The researchers determined that conditions for intraoperative mapping were excellent in all cases, allowing for multimodal motor, sensory and language assessment. Interestingly, although all patients had fMRI-based surgical plans, intraoperative mapping provided additional functional and anatomic information that was not offered by the preoperative scan. “In 24% of patients, the intraoperative surgical plan changed based on new data acquired from the intraoperative brain mapping,” Dr. McAuliffe said.
“In 31% of patients, new information from the brain mapping resulted in the surgeon asking us to keep the patient awake during the period of stimulation and tumor resection to facilitate ongoing subcortical stimulation throughout the procedure,” she added.
In addition, 95% of patients had favorable brain tension as recorded by the neurosurgeon in the operative note. “Only 5% of patients required perioperative mannitol use,” she said. “Looking at other reports in the literature, mannitol has been used in up to 54% of patients, although this is obviously dependent on the type of surgery and the surgeon in question.”
No significant hemodynamic instability was observed in any patient, according to Dr. McAuliffe. “Even though dexmedetomidine has been shown to have dose-dependent effects on the cardiovascular system, we didn’t see any critical changes in the blood pressure during that time.” One episode of significant bradycardia requiring glycopyrrolate was observed; this occurred in a patient receiving dexmedetomidine at the rate of 1 mcg/kg per hour. Hospital length of stay was approximately two days, which Dr. McAuliffe said “compares very favorably with general anesthesia for awake craniotomy, which is associated with lengths of stay between five and seven days.”
There were no critical events that required rescue of an obstructed airway, and no patient required airway instrumentation or conversion to a full general anesthetic. Intraoperative nausea and vomiting did not occur, and no local anesthetic toxicity was observed. “Intraoperative seizures occurred in 16% of patients; all were limited by the administration of topical cold saline,” she added. “We had no general seizures on stimulation, so all the local seizures occurred at the time of direct cortical stimulation.” Finally, the investigators observed a very high level of patient engagement and satisfaction with the technique.
“In conclusion, our results show that dexmedetomidine and scalp blocks allow for optimal conditions for intraoperative brain mapping without the need for airway intervention,” Dr. McAuliffe said. “Intraoperative brain mapping resulted in a change in surgical plan in up to a quarter of patients, highlighting the importance of being able to test a patient in an interpretive fashion for brain mapping, especially for tumors near eloquent regions of the brain. And most interesting, physiological parameters remained stable throughout the procedures with our doses of dexmedetomidine.”
The lack of airway manipulation coupled with titratable levels of sedation provided excellent conditions for intraoperative mapping and patient cooperation. However, the researchers recognized the need for a prospective trial to assess clinical outcomes, such as the duration of disease-free survival, time to tumor recurrence and the overall quality of the patient experience.