Stereotactic localization of bilateral entry points is performed and these areas are then marked. The head is shaved, prepared, and draped in the standard sterile fashion. Incisions are opened and meticulous hemostasis achieved. Two 14-mm bur holes are then drilled bilaterally centered over the prior stereotactic localization points. A number of frame, miniframe, or frameless systems are now available; however, the general principles are similar. Registration is performed with the intraoperative navigation station and less than 0.5 mm error is preferred.

Once exposure is achieved, physiological microelectrode recording is performed to achieve optimal electrode positioning. It is a key point to remember that the stereotactic coordinates represent the starting point for target identification, but that the end target is identified in the operating room.

The dura, pia, and cortical surface are coagulated and incised on one side, beginning contralateral to the patient’s worst symptoms. The trajectory is aligned using the previous target and entry projection. Initial depth is commonly set to 10 mm above target, ensuring that the patient’s blood pressure is normotensive. Electrophysiological activity is typically used to identify exact targets. This is done by microelectrode recording and microelectrode stimulation followed by macrostimulation. The microelectrode is advanced in a stepwise fashion, continuously recording. A DBS electrode is then measured to the appropriate length and introduced to the target point (Fig. 32.2). Test stimulation is carried out with the goal of minimal adverse effects with good therapeutic benefit. Once the lead position has been confirmed, the outer cannula is withdrawn and a skull fixation device is fastened to ensure that the electrode is held firmly in place. The leads are connected to temporary externalized extensions for a trial phase of stimulation.

In the postoperative period, close attention to blood pressure control is performed and the postoperative CT or MRI performed to confirm accurate electrode placement and to rule out any evidence of intracranial hemorrhage. In general, combined stimulation of periventricular gray (PVG) and ventral posterior lateral thalamus (VPL) has been superior to single-lead stimulation. In most patients a certain subperception threshold is needed to produce a pain-relieving effect. If appropriate and acceptable pain relief is achieved, the patient is brought back to the operating room, where the temporary connector is removed and a permanent extension cable is used to connect to the lead to the implanted pulse generator. A subcutaneous pocket is prepared for the internal generator and the extensions are passed through the subcutaneous tissue to connect the system. If the system fails to provide relief, the patient is not a candidate for a permanent device, and the lead is explanted.