Stereotactic Procedures

Stereotactically guided procedures are performed for numerous indications, including biopsy of small deep-seated lesions, placement of deep brain stimulation electrodes (for Parkinson's disease and other movement disorders), and ablation of lesions (for movement disorders and temporal lobe epilepsy). The future may also bring placement of intraparenchymal stimulators for control of epilepsy and stereotactic stem cell implantation for a variety of degenerative and ischemic disorders. The issues with which the anesthesiologist must contend include restriction of airway access by the frame, restriction of sedative latitudes when electrophysiologic recordings are to be performed as a guide to device placement, and detection and management of complications (principally intracerebral hematomas).

Preoperative evaluation should include attention to ensuring that the coagulation process is intact and that the patient has not been taking platelet-inhibiting agents (including herbal medications). Patients should be given a careful explanation of the procedure, its probable duration, and the necessary restraints on movement.

Commonly, the stereotactic frame, of which there are many variations, is placed with the use of a local anesthetic, and the patient undergoes an imaging study before being brought to the operating room. In some instances, the frame will prevent application of the mask and ventilation, laryngoscopy, or neck extension. If a general anesthetic is to be administered, awake intubation may be required. If sedation is to be used, the anesthesiologist should have certain knowledge regarding how to remove the device rapidly in an urgent situation (including knowledge of the whereabouts of the requisite "key" or spanner device).

When electrophysiologic recordings are not intended, sedative regimens similar to those used for awake craniotomy (see the preceding section, "Head Injury") may be appropriate. However, for placement of thalamic and subthalamic stimulators, part of the localization process entails identifying the typical electrophysiologic "footprint" of specific nuclei. Because the nature and duration of the effects of anesthetics on these signals are not known systematically, some surgeons may request that no sedative whatsoever be given. If sedatives are administered, they must be given in a manner that ensures the ability to perform precise intermittent neurologic examination of the patient. An issue that arises in some patients with movement disorders (e.g., Parkinson's disease) is the problem of obtaining high-quality radiologic images in the presence of a persistent tremor. Sedation immediately preceding stereotactic placement may therefore be inevitable. Propofol has been used, but the window between propofol administration and subsequent recording should be as long as possible. Dexmedetomidine has also been used and has been reported to us to be very effective in suppressing movement in patients with Parkinson's and other movement disorders in doses that maintain patient responsiveness and respiration (Mary K. Sturaitis, M.D., personal communication).

During the subsequent procedure, among the anesthesiologist's objectives is the prevention or treatment of hypertension. The concern is that in the face of multiple needle passes through the brain, hypertension will precipitate the development of an intracerebral hematoma. In the event of a substantial hematoma, an urgent craniotomy may be required, and the anesthesiologist should be prepared from the outset for this eventuality. These procedures are lengthy, and restlessness may occur, especially in unsedated patients. The nonsystematic experience, obtained in situations in which the options were to sedate the patient or abandon the procedure, has been that satisfactory recordings can be made in the presence of dexmedetomidine. That drug has the advantage that it also contributes to the control of hypertension (Mary K. Sturaitis, M.D., personal communication).