Abstract
Introduction
Severe persistent pain following back surgery is often referred to as failed back surgery syndrome (FBSS). FBSS is a debilitating chronic neuropathic pain condition, affecting approximately 10 to 40% of patients after lumbosacral spine surgery. Treatment of FBSS is challenging as conservative therapies and repeated surgery often fail in providing adequate pain relief. Spinal cord stimulation (SCS) has proven to be an effective therapeutic modality for the treatment of certain chronic pain syndromes, including FBSS, pain associated with peripheral vascular disease, peripheral neuropathies, multiple sclerosis, and complex regional pain syndrome. SCS low voltage stimulation of the spinal nerves used to block the feeling of pain called “gate control” theory. The standard practice for placement of spinal cord stimulators requires direct interaction with the patient, which means the patient needs to be awake and alert enough to respond to sensations generated from stimulation. SCSs could be placed under general anesthesia (GA), with intraoperative neurophysiological guidance during SCS placement.
Materials and Methods
Patients were brought to the operating room and put under GA using standard intubation performed. EMG was recorded from upper or lower limb muscle groups related to the placement of the stimulator electrode. Lateralization was performed based on EMG responses and electrode pairs stimulated. Stimulation is applied through the SCS electrodes. Initial stimulation testing parameters were 60 Hz and 210 µ seconds. These were chosen based on common parameters used during pain control therapy with SCS. Amplitude would be then slowly raised in 0.5 V or 0.5 mA increments until EMG activity is noted in any channel. At that point, increases in stimulation are halted and the location of this threshold EMG activity is noted (amplitude, side(s) and muscle(s)). Amplitude is then increased in 0.5 V (mA) increments further until a new (additional) location of activity is detected. Once all data has been obtained in this fashion, we determine the spinal cord midline on the electrode array and plot it.
Results
We found that when all left column electrodes are only activated with stimulation of the left side of the electrode and all right side muscles are only activated with the right side electrodes, then the midline is close to the center. The center column test helps to focus the centerline. Depending upon the side of activation, differences in voltage or current thresholds for EMG between the sides, and differences between the top and bottom sets of electrodes, the paddle orientation can be determined within approximately 1 mm. In many cases, the desired location of the lead is slightly off to one side of laterality. It should be noted that in our experience with this technique and lead adjustments, there is roughly a sensitivity of about 1 mm wherein thresholds of activation may be altered by lead location. Another element used in centerline localization is the amplitude of activation. In many cases, the electrodes very close to the dorsal median sulcus of the cord counter intuitively require greater amplitude to activate EMG than the electrodes that are placed more laterally. If the electrodes are placed too lateral (for example the electrode is completely on one side of the cord) the amplitude required to activate EMG is also greater, and may not even occur. The number of times that the electrode was repositioned from the initial starting test position based on the above localization technique was also reviewed, as this would indicate a direct measure of the decision-making contribution this method affords. Postoperative programming of patients was typically started within 3 hours of surgery prior to discharge. At this session, a basic localization paradigm was used where the programmer tested quadrants of the lead and noted the initial sensation location on the body. A more detailed programming session was performed at 10 to 14 days postsurgery when the patient was much more alert, devoid of all anesthetic effects and when surgical pain had diminished. This “dermatomal” data was compared to the “myotomal” intraoperative data with no significant difference.
Conclusion
SCS can be an effective alternative or adjunct treatment to other therapies that have failed to manage pain on their own. SCS may be an option in selected cases, particularly when pain is largely neuropathic in origin. Several groups have begun using neurophysiological methods for paddle-lead placement in SCS surgery, allowing for the concomitant use of GA. This approach eliminates one of the largest risks with an awake technique (the possibility of over sedation and loss of airway control) and makes the role of anesthesiologist, surgeon, and patient more comfortable. Such an approach arguably broadens the palatability of placing paddle-type leads in general, making them able to be both safely and accurately placed. We utilize parameters similar to therapeutic values for testing, and in validating the technique by showing the overwhelming match of intraoperative myotomal stimulation to postoperative dermatomal sensations. Moreover, we have obtained a deeper understanding of the value of neurophysiology during these procedures.
Yes
None declared
Mammis A, Mogilner AY. The use of intraoperative electrophysiology for the placement of spinal cord stimulator paddle leads under general anesthesia. Neurosurgery 2011
Duyvendak W. Spinal cord stimulation with a dual quadripolar surgical lead placed in general anesthesia is effective in treating intractable low back and leg pain. Neuromodulation 2007;10(2):113–119