Contraindications
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Patients who are unable to cooperate because of psychosocial issues or young age.
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Patients with airway concerns, including sleep apnea and obesity.
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Patients whose preoperative language baseline is less than 80% of objects named correctly at 4-second intervals. Because stimulation language mapping relies on the ability to block object naming, language cannot be localized when baseline errors are too high. Although some object slides can be discarded from the specific patient’s slide set, the final set should have at least 50 slides. When the patient has normal naming ability (i.e., 100% of slides named correctly), slides are presented at 3-second intervals. This allows quicker mapping with a higher current because of less temporal current summation.
Planning and positioning
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All local anesthetics used comprise 1% lidocaine and 0.25% bupivacaine with 1:200,000 epinephrine. Typically, 80 to 110 mL of this mixture is administered.
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The patient’s head must always be lateral or angled slightly above the horizon so that the airway is well protected and the patient can see the computer screen. Attention is directed toward positioning the head to optimize the patient’s airway during sedation. Although we prefer to use the pin headrest, the procedure can be done with a horseshoe headrest or even a foam donut. Pins provide the greatest degree of head stability, however.
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A Foley catheter is always placed.
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Patients should have therapeutic serum levels of antiepileptic medication preoperatively.
Figure 39-1:
Applying a pin headrest after instillation of local anesthesia.
Figure 39-2:
The patient is turned to a 45- to 60-degree lateral position with the bed in 15 to 25 degrees of reverse Trendelenburg. All pressure points are carefully padded with the neck slightly extended to improve airway patency during propofol (Diprivan) anesthesia.
Figure 39-3:
Scalp fiducial markers are registered to preoperative magnetic resonance imaging (MRI) using the frameless neuronavigation system.
Procedure
