Spinal cord stimulation (SCS) lead implantation is a common and effective procedure for the treatment of chronic pain (1–3). Depending on the type of lead, access to the spinal canal can be performed percutaneously or by surgical laminectomy (4–7). For optimized lead positioning, it is required that the patient be awake and able to locate the paresthesias, as precise lead placement determines success. Neuraxial anesthesia and sedation are used for patient comfort during percutaneous access. Some authors feel that laminectomy access has several advantages, such as a wider surgical area with more testing and positioning possibilities, easy and accurate final lead anchoring, and minimization of traumatic dural and neural injuries (8,9).
Our group proposes neuraxial epidural block as a suitable anesthetic for SCS lead placement with laminectomy.
After obtaining approval by the Independent Ethics Committee in our center and patients' informed consent, we enrolled 31 subjects consecutively in our study, with ASA physical status II-III and neuropathic pain syndrome.
All patients had been previously diagnosed with failed back surgery syndrome, defined as persistent or recurrent pain after lumbosacral spinal surgery, with a chief complaint of radicular pain. Patients were selected for SCS (after a trial using the criteria of the Pain Unit) and were then implanted with a laminectomy lead by the neurosurgeons in our hospital.
Pain Unit Criteria
Patients with lumbosacral root injury pain (persistent or recurrent pain after lumbosacral spinal surgery) were included in the study on the basis of the following criteria. The first was the chief complaint of radicular pain, as opposed to axial low back pain; eligible patients described their midline or axial low back pain as being less than, or equal to, their radiating hip, buttock, or lower extremity pain. The second criterion was an objective basis for the complaint of pain beyond the history of prior low back surgery. One or more of the following was required: 1) recent abnormal diagnostic imaging results (e.g., myelogram demonstrating lumbar arachnoid fibrosis), 2) a neurological deficit consistent with the patient's pain complaints and history, and/or 3) a well-documented history of surgery for appropriate indications.
The criteria for passing the trial were the generally accepted reported reduction in pain by 50% or more (using standard, self-reporting methods) in the presence of stable or reduced analgesic use and changes in physical activity that reflected this pain relief during the trial period. The patients who passed the trial received a permanent implant at exactly the same level, with half of the patients randomly assigned to receive a percutaneous electrode and half an insulated electrode implanted by laminectomy.
Patient Exclusion Criteria
Exclusion criteria were aspirin intake within 6 days before surgery, a platelet count <150 × 109/L, an international normalized ratio >1.1, active neurological disease, cutaneous disorders at the epidural insertion site, and major psychiatric illnesses or abnormal illness.
Patients were monitored during anesthesia and in the postanesthesia care unit according to standards and guidelines published by the ASA.
We inserted the epidural catheters at the T10–11, T11–12, T12–L1 interspaces using a midline and loss-of-resistance technique. We injected 8–10 mL of 0.375% ropivacaine. Analgesic level for the surgery, if required, was attained by the additional injection of 4–6 mL of 0.375% ropivacaine. The epidural catheter was removed after an appropriate sensory level of blockade was obtained and before the laminectomy was performed.
Lead Implant Procedure
We inserted the octopolar lead (model 3998 Specify®, Medtronic Inc., Minneapolis, MN) in the epidural space by a thoracic hemilaminectomy (performed in T10–11) and then advanced the lead one or two vertebral levels cephalad under fluoroscopic control. Lead position was either midline or slightly lateral, as verified with radiographic and clinical intraoperative patient testing. Intraoperative testing was performed with a dual channel paresthesia analyzer (DualScreen, model 3628, Medtronic Inc., Minneapolis, MN), each channel comprising 4 of the 8 electrodes.
The final position of the SCS lead was the vertebral level that provided coverage of the patient's pain (state back pain if the pain is axial, do not state back pain if the pain is radicular in location) at the lowest amplitude.
To define the patient's degree of comfort during the surgical procedure we used the visual analog scale pain score (VAS; 0 = no pain, 10 = worst possible pain) and the Richmond anxiety-sedation scale (10) [agitated patient (+4 to + 2), mild anxiety (+1), calm (0) and sedated patient (−1 to −5)]. Before the operation, patients were instructed about the use of VAS.
All variables were tested for normal distribution using the Kolmogorov-Smirnov test. Normally distributed variables are expressed as mean (±sd) value. Aside from descriptive statistics, Student's t-test was used to compare variables (SPSSR v. 13, Chicago, IL).
Thirty-one patients were enrolled in the study from June 1, 2004, to November 1, 2005. Patients underwent psychological screening before lead implantation. Since epidural puncture could not be performed in seven patients, the final study sample size was 24 patients (Table 1). Technical failure was defined as two failed attempts by expert anesthesiologists or inability to advance the epidural catheter one or two vertebral levels. General anesthesia was used for the patients in whom the epidural could not be placed.
Epidural puncture variables are presented in Table 2. Our results indicate that patients achieved a good degree of comfort during the procedure, as all patients had VAS score <2 (no pain or low pain) and no patient had moderate or severe pain. Our patients were either calm or mildly anxious during the procedure; 20 had Richmond scale scores of 0 whereas 4 had scores of +1, none required additional anxiolytics or sedatives.
The mean (sd) total intraoperative time was 133.5 (20) min. We found statistically significant differences between intraoperative and postoperative (at 24 h) stimulation variables needed to reproduce paresthesias. The mean (sd) intraoperative and postoperative channel 1 stimulation intensities (V) were 4.3 ± 1.5 and 3.2 ± 1.3, respectively, (P < 0.05) whereas the channel two stimulation amplitudes were 4.6 ± 1.3 and 3.4 ± 1.1 respectively (P < 0.05).
The use of SCS has increased in the last decade as it has proven effective for patients suffering from chronic neuropathic pain resistant to alternative treatments (11–14).
In our study, we demonstrate that epidural anesthesia is a suitable technique for SCS lead implant. Satisfactory analgesic level was obtained by epidural block in 100% of the patients (VAS score ≤2) without additional sedation or patient discomfort. However, 22.5% of our subjects could not be anesthetized by the epidural route using conventional loss-of-resistance technique. Our failure rate of 22.5% is similar to others (15) who showed failure rates of 32% with thoracic epidural placements and 27% with lumbar placements. The inability to place the epidural in some of the patients with failed back surgery syndrome requires an alternative plan that includes moderate sedation. General anesthesia may not be the best alternative, since intraoperative testing of paresthesia is needed for appropriate lead placement. Alternatively, use of fluoroscopic guidance for epidural anesthesia may substantially improve the success rate and obviate frequent need for a general anesthetic plan.
Previously described anesthetic techniques include local and spinal anesthesia. A larger study (16) was unable to provide information on patient discomfort when laminectomies are performed solely under local anesthesia. Lind et al. (1) described, for the first time, lead implantation by laminectomy under spinal anesthesia. We prefer epidural over subarachnoid anesthesia because of better hemodynamic stability, absence of meningeal puncture, and the flexibility of continuing anesthesia through the epidural catheter.
There are several reasons why, under neuraxial anesthesia, patients feel paresthesia during SCS lead placement. The epidural local anesthetic acts mostly at the nerve roots and pain sensation is inhibited mainly in the affected dermatome. The L5–S1 nerve roots are usually not completely numbed by epidural anesthesia, since these nerve roots are hard to completely block because of their wide nerve root diameters (17). The spinal cord is not completely blocked by the local anesthetic and the patient feels paresthesia with SCS stimulation (18–20). The impulse transmission in the dorsal columns of the spinal cord is not completely blocked with epidural anesthesia, even in the presence of complete numbness on sensory examination (21).
The increased use of SCS is supported by studies that have better identified the indications for its use (16,22,23). Despite being a more invasive technique than the percutaneous approach, better long-term results were noted after SCS placement with laminectomy in terms of pain relief, return to work, and improvement in the patients' activities of daily living (24). Although the initial costs are high, mid- and long-term benefits were noted in health care utilization (14,25,26). Complications of SCS placement are generally minor, easily treatable, and rarely involve trauma to the spinal cord.
In conclusion, this is the first study on the use of epidural anesthesia for SCS lead implantation under laminectomy. The use of epidural anesthesia provides an awake patient and identification of paresthesia resulting in the optimal placement of the SCS leads. Our limited case series suggests that the technique is effective after establishment of epidural anesthesia. However, the high rate of technical failure of epidural anesthesia using the conventional loss-of-resistance technique in these patients suggests that imaging modalities may be useful to improve the success rate.
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