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PART FIVE  METHODS FOR SYMPTOMATIC CONTROL

(previously Advanced Bionics Inc, Natick, MA), Medtronic Inc (Minneapolis, MN), Nevro Corp (Redwood City, CA), Nuvectra Corp (Plano, TX), and Stimwave (Pompano Beach, FL). CHOICE OF ELECTRODE Percutaneous catheter electrodes are available with up to 16 con­ tacts and can be implanted singly, creating a one-dimensional array or multiply, creating a two-dimensional array. Multiple percutaneous electrodes can be introduced one by one through a Tuohy needle to rest side by side. Use of three or more such electrodes in parallel permits programming of lateral anodes “guarding” a central cathode, which might mitigate dorsal root recruitment causing uncomfortable side effects; however, it can be difficult to achieve and maintain appropriate spacing be­ tween electrodes. Figure 96.7 illustrates a selection of available electrodes. An important role remains for plate/paddle electrodes, which cannot be introduced through a needle and thus require surgical exposure via laminectomy. These electrodes have as many as 32 contacts in multi-column configurations and are insulated to prevent excess stimulation of dorsal structures. 189 The spacing of the columns is fixed, precluding adjustment as well as postop­ erative migration of one column with respect to another. Factors that dictate choice of electrode include the location of the pain, the amount of extraneous stimulation that must be managed, and the physician’s qualifications and experience (anesthesiologists, e.g., might be expected to use only percuta­ neous electrodes). CHOICE OF PULSE GENERATOR Pulse generators are distinguished by their power sources and output configurations. The earliest systems incorporated a small radiofrequency receiver with no implanted battery,

ELECTRODE POSITIONING Ideally, patients remain conscious during trial electrode place­ ment under local anesthesia in order to describe paresthesia coverage and have the opportunity to react to changes in stim­ ulation parameters or unanticipated intraoperative events. Evoked potential techniques may be used when general anes­ thesia is required, as for example in some cases of paddle elec­ trode implantation. 188 PARAMETER ADJUSTMENT Trained professionals work with patients to adjust simulation pa­ rameters during the screening trial and after implantation to find the settings that maximize comfortable pain/paresthesia over­ lap, reduce or eliminate extraneous stimulation, and minimize power requirements. Even when paresthesia-free stimulation settings will ultimately be used, this may be presumed to be the best method for selection of the electrode contacts. Patients are instructed at each stage so as to operate the device appropriately. PROCEDURAL RISK REDUCTION Implanting an electrode for a screening trial or chronic stim­ ulation is associated with certain risks, including spinal cord or nerve injury, dural puncture, epidural hematoma, and in­ fection. Risk can be reduced by ordering a preimplant MRI of the target spinal levels, performing the procedure under fluo­ roscopy with the patient conscious, maintaining a meticulously sterile environment, administering prophylactic antibiotics, and observing the patient for a reasonable length of time post­ procedure (e.g., overnight). Discharge instructions must indi­ cate when and how patients should contact their physicians, the device manufacturer, and emergency care providers. TRIAL DURATION A typical screening trial with a temporary percutaneous elec­ trode lasts a week. In some circumstances, a shorter trial will be adequate, whereas in others, a longer trial might be beneficial. The role of a screening trial is subject to change with recent technical developments: As more and more waveforms become available, and as some patients need to try multiple settings to achieve a satisfactory result, trial duration can increase to an extent causing undue risk of infection. Externally powered im­ plants which can be inserted in their entirety through a needle might mitigate this problem. 189 REMOVAL OF TRIAL ELECTRODE Using the same percutaneous catheter electrode for screening and permanent stimulation would reduce the cost of the hardware, but this savings would be offset by the increased cost of anchor­ ing the electrode, which must take place in an operating room. Anchoring a trial electrode for potential permanent stimulation also increases incisional pain, which might confound interpreta­ tion of the trial; anchoring also requires use of a percutaneous extension cable, which increases the risk of infection. On the other hand, a percutaneous catheter electrode designed solely for screening is relatively inexpensive, can be inserted under sterile conditions with fluoroscopy, and can be removed easily. Using the same electrode for the screening trial and per­ manent stimulation might eliminate the possibility that the replacement electrode will not reproduce the pain/paresthesia overlap, but this strategy also eliminates the opportunity to im­ prove on the results of the screening trial—which can inform the patient as well as the physician. Device Options In alphabetical order, the major manufacturers of SCS equip­ ment are Abbott (previously St. Jude’s Medical, previously Ad­ vanced Neuromodulation Systems, Plano, TX), Boston Scientific

FIGURE 96.7  Percutaneous catheter electrodes (top left) have as many as 16 cylindrical contacts designed for introduction through a needle. Lam- inectomy electrodes (bottom) have evolved (left to right) from a single column of contacts to as many as seven columns or centerlines, with as many as 32 contacts.