Anesthetic Considerations for Awake Craniotomy for Epilepsy ... - Vtr

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Erickson & Cole
Medications
Several specific medication effects have been studied with regard to awake craniotomy
for epilepsy and functional neurosurgery.
Propofol, although providing good patient satisfaction and antiemetic and antiepileptic
effects, may cause oversedation and poor operating conditions. Propofol is
associated with hypoventilation, although this is less of a problem when a targetcontrolled
infusion is used or when opioids are not added. 114,134 During DBS insertion,
less propofol may be required in patients with Parkinson disease than is predicted by
target-controlled infusion models. 167
Opioid-based techniques are associated with increased reports of seizures and
nausea. 142 Among opioids, none of the short-acting fentanyl congeners, including
the ultra–short-acting remifentanil and alfentanil, used for awake craniotomy has
been shown to be superior to its peers. Comparisons of fentanyl with sufentanil and
alfentanil, and remifentanil with fentanyl, do not show any differences in complications
and all provided good clinical conditions although a case report described severe
remifentanil-induced opioid tolerance in a 16 year old. 118,142,168 The desirable brevity
of action common to these opioids may require the use of a longer-acting opioid for
postoperative pain control. 168 The problems of respiratory depression and increased
brain volume (discussed previously) as well as airway obstruction and desaturation are
common to all opioids.
Dexmedetomidine, the selective a2-agonist, has been used for both MAC and AAA
management of awake craniotomy and DBS implantation since the first case report
by Bekker and colleagues in 2001. 141,150,151,154,161–166,169 The successful use of dexmedetomidine
has even been reported in children as young as 12 years. 163,166 Dexmedetomidine
provides analgesia with minimal respiratory depression (little risk of
hypercapnea), cooperative sedation, anxiolysis without agitation or hangover effect,
and hemodynamic stability. Lower doses are suggested for awake craniotomy,
because higher doses can impair patient responsiveness. 170 It may be used alone for
sedation and analgesia, or with volatile, nitrous oxide, or total intravenous anesthesia
as an adjunct to smooth induction, and emergence. Dexmedetomidine alone may be
ideal for DBS implantation because it does not depend on GABAergic pharmacology
and also does not suppress target symptoms, such as tremor or dyskinesia. 137,153,154
High-dose dexmedetomidine, however, has been shown to interfere with MERs. 137
Likewise, Oda and colleagues 152 reported changes in ECoG recordings during epilepsy
surgery with dexmedetomidine use at higher doses (discussed previously). The main
disadvantages of dexmedetomidine include hypotension and bradycardia, which are
reported to be dose related and treatable, if not preventable. 171
Anesthetics and Microelectrode Recordings
One of the main purposes of the awake state for DBS placement is to avoid interference
of general anesthesia with MERs from deep brain structures.
Benzodiazepines seem to abolish MERs and may induce dyskinesias. 103,128,172
Although there are no prospective data, it seems that anesthetics do not uniformly
depress MERs but rather differ by disease as well as by deep brain site/nuclei. For
example, desflurane seems to depress MERs from the globus pallidus internus (GPi)
in Parkinson disease but not in dystonia. 173 Reports of GPi recordings, both unaffected
and depressed by propofol, have been published. 135–137,154,174–176
In contrast, MERs from the subthalamic nucleus (STN) seem relatively more robust
under anesthesia, which has been attributed to its lower GABA input compared with
the GPi. 177 Benzodiazepines seem to abolish MERs and may induce dyskinesias. 172