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

256
Erickson & Cole
Seizure
Intraoperative seizure is a risk in this population. Although reports suggest seizures
occur infrequently, 50 an unchecked seizure in awake patients in pinion with an unsecured
airway is a potential crisis. During DBS implantation, one prospective study of
complications reported a seizure rate of 0.06% (as a percentage of procedures), 183
whereas other reports range from 0.8% to 4.5% of patients. 169,179,188,189 Although
confounded by duplication in published data, the largest literature review of seizures
reports a range of 0% to 10% but without a clear explanation for the variation. 190 The
majority (74%) of seizures occurred near the time of lead implantation and many of
these patients also sustained intracranial hemorrhage. 190
Suggested risk factors for seizure include abnormality on postoperative imaging
(hemorrhage, edema, and ischemia), 189 hemorrhage, 189,190 age greater than 60 years, 189
transventricular electrode trajectories, 189 and multiple sclerosis. 191 Fortunately, seizures
stimulated by cortical mapping during craniotomy for epilepsy are usually aborted by the
surgeon stopping the stimulation or delivering ice-cold saline directly onto the cortical
surface. Seizures that are spontaneous or do not stop with these measures are treated
with small doses of benzodiazepine, propofol, or barbiturate. Rarely do these require intubation.
A postictal period may interfere with neurocognitive testing.
Hemorrhage
Bleeding is one of the most feared surgical complications during DBS implantation
because it is less easily controlled through a bur hole than via an open craniotomy and
because of the functional structures at stake in the area of bleeding. Fortunately, it is
rare. Reported frequency of bleeding ranges from 0.9% per procedure192 to 2.2% 179 to
10% 183 andupto34.4%. 106 In Zrinzo and coworkers’ review of consecutive cases (214
patients, 417 electrodes), 0.5% of hemorrhage was asymptomatic, 0.5% was symptomatic,
and 0% resulted in permanent deficit. 192 The investigators identified hypertension
and age as risk factors and excluded diagnosis, gender, and previous use of anticoagulants.
192 Surgical risk factors associated with hemorrhage included the use of MERs (in
contrast to “image-guided and image-verified” or macrostimulation-guided lead placement),
number of microelectrode passes, and transventricular lead trajectories. 192
Hemodynamic Instability
Hemodynamic changes, including hypertension, hypotension, and tachycardia, were
found more frequent, albeit not harmful, to patients when promptly treated with awake
craniotomy by the AAA technique than under general anesthesia. 50 During DBS insertion
in awake patients, hypertension has been associated with intracranial hemorrhage.
104,193 In one report of 172 DBS procedures plus 6 ablative procedures, 3.9%
of patients had systemic arterial blood pressure greater than 160/90 mm Hg for 2
consecutive readings 5 minutes apart (3.9%). 179 Five of 6 patients had a history of
hypertension, and all were treated without sequelae. 179 Nevertheless, hypertension
requires prompt treatment. Two investigators suggest goals for systolic blood pressure
of less than 140 mm Hg or no more than a 20% to 30% decrease from a patient’s
usual level. 154,193 Rozet and colleagues154 found improved blood pressure management
and less use of antihypertensive medications in patients who were given dexmedetomidine
compared with unsedated patients.
Venous Air Embolism
Venous air embolism in awake craniotomy patients is apparently no more frequent
than in craniotomy under general anesthesia. 194 In the sitting or semisitting position