a total of 23 patients with chronic intractable lower limb pain who had permanent scs with a cylindrical type under epidural anesthesia between november 2010 and december 2013 were included in the case series . all patients had previously undergone a successful scs trial with percutaneous electrodes for more than 3 days . a successful trial of scs was defined as pain reduction or the satisfaction rate  50% with evidence of increased activities . the percutaneous trial leads were removed and discarded regardless of the success of the trial . written informed consent was obtained from each patient the day before the permanent lead and the generator was placed . electrocardiogram , blood pressure and peripheral oxygen saturation were routinely monitored throughout the procedure in the operating room . the patient was placed in the lateral decubitus position with the spine flexed for epidural anesthesia . two percent lidocaine was infiltrated around the needle puncture site prior to the epidural anesthesia , which was induced by epidural bolus injection at the l2-l3 , l3-l4 or l4-l5 level with local anesthetic solution in volumes from 10 to 30 ml to achieve the sensory blockade of t10 or higher . the volume and dosage of local anesthetics for epidural anesthesia were decided arbitrarily by the discretion of the responsible anesthesiologist . the patient was then arranged in the supine position and checked for the anesthetic level using a blunt needle every 5 min . the patient was placed prone with a pillow under the abdomen to reduce lumbar lordosis after an appropriate sensory level of block was obtained . after the sterile skin preparation and draping was performed , fluoroscopic anteroposterior ( ap ) imaging was used to identify and mark vertebral segments and pedicles of l2 , l3 and l4 with a sterile marker . a 5 cm long longitudinal skin incision was made aligning the centers of l2 , l3 or l4 pedicle after the incision site was checked . a 14 gauge tuohy needle was used for the paramedian approach with c - arm fluoroscopic image . after ensuring that the needle was positioned in the epidural space , the guidewire was used to make insertion of the electrode easier . the octode electrode lead ( advanced neuromodulation system , planco , tx , usa ) was carefully advanced through the needle to one vertebral level above to the target placement , and then the lead placement was determined by the patient response during intraoperative stimulation . successful stimulation was defined as paresthesia development in the patient 's pain distribution area as in the trial stimulation . fluoroscopic images in both ap and lateral views were taken after determining the placement of the lead . if a second lead was required , the second epidural needle was inserted inferior to the first needle . after stylet and the needle were removed under fluoroscopic guidance , the leads were meticulously anchored with a 2.0 nonabsorbable silk . final fluoroscopic images in both ap and lateral views at the end of this process were taken to ensure that lead migration did not occur . a small incision was made in the flank below rib 12 for the exit of the lead , and then a tunnel was made in the deep subcutaneous fat by using a tunneling tool from the back incision . after irrigation of the lumbar incision area with a mixed solution of normal saline and antibiotic , it was closed and dressed . after the patient was placed in the left semilateral position , sterile skin preparation and draping a transverse incision about 5 cm long was made along the previously marked line in the left lower abdominal region just below the umbilicus level and subcutaneous pocket was created caudal to the incision . the pocket site was irrigated with a mixed solution of normal saline and antibiotic , and sutured . appropriate dressings covered all the wounds . the scs was turned on and tested again to ensure adequate coverage of all painful areas after the patient had been completely recovered from epidural anesthesia . scs parameters were recorded and compared at the trial ( t0 ) , permanent implant ( t1 ) and postoperative stimulation 3 days after surgery ( t2 ) . the pain intensity was evaluated with a visual analogue scale ( vas ) of 0 to 10 ( where 0 means nothing and 10 represents the worst condition imaginable ) before and after the permanent scs implantation . twenty - three patients underwent epidural anesthesia for permanent scs implantation ( table 1 ) . epidural anesthesia was sufficient to perform the implantation of the lead and generator in 22 patients without interference with the intraoperative test stimulation . incomplete epidural anesthesia requiring an additional dose of fentanyl 100 ug to control pain was experienced in one case . there was an interval of 15.2  6.7 days between the trial and permanent scs implantation . the highest level of the sensory block was the fourth thoracic segment ( 9.5% ) and the lowest level was tenth thoracic segment ( 4.8% ) , which provided sufficient analgesia for all scs procedures . the epidural local anesthetics included 2% lidocaine in three patients , 0.75% ropivacaine in one patient and a mixed solution of 2% lidocaine and 0.75% ropivacaine in 19 patients . the average volume of local anesthesia was 16.4  4.3 ml ( range 10 - 30 ) . hypotension and bradycardia were treated well with volume expansion , ephedrine , phenylephrine or atropine . all the leads were placed according to the patient 's report of paresthesia coverage when stimulations of spinal cord were created under the epidural anesthesia . the electric current variables ( ma ) needed to reproduce paresthesias at t0 , t1 and t2 were 1.87  1.02 , 5.27  2.13 and 2.47  0.86 , respectively . the electrical current intensity at t1 was significantly higher than those at t0 ( p < 0.001 ) and t2 ( p < the frequency ( hz ) at t0 , t1 and t2 ranged from 30 to 60 , and the pulse width ( s ) at t0 , t1 and t2 ranged from 200 to 300 . all patients experienced pain improvement ( table 2 ) and the average pain intensity ( vas ) scores were 8.6  0.6 and 3.6  0.6 before and after scs implantation . it has been generally considered that adequate paresthesias may not be obtained if the nerve roots or the spinal cord are blocked by epidural anesthesia . however , this report demonstrates that successful epidural anesthesia in scs implantation without disturbing perception . during the procedures , epidural anesthesia provided a satisfactory analgesic effect , with the exception of one patient who felt pain , which was controlled by intravenous fentanyl 100 ug . hypotension and bradycardia were the most common cardiovascular changes during the epidural anesthesia for scs , requiring careful managements of blood pressure and heart rate . scs can be used for a variety of anesthetic techniques including local anesthesia , local anesthesia with sedation , spinal anesthesia , epidural anesthesia , monitored anesthesia care and general anesthesia . scs is generally performed under local anesthetic infiltration with or without sedation considering intraoperative test stimulation . local anesthesia does not prevent the patients from suffering significant discomfort and stress , and occasionally some patients have to abandon the procedures . increased administration of sedatives and analgesics in the prone position may cause airway problems and respiratory depression . excessive sedation and general anesthesia prevent the patient from responding to the distribution of paresthesias for optimal positioning of the lead . garca - prez et al .   reported that epidural anesthesia is suitable for identification of paresthesia in the optimal placement of the scs leads . zhang et al .   suggested that patient 's perception of paresthesias during intraoperative testing is reliable , consistent and correlates well with the postoperative stimulation . epidural anesthesia was an effective and safe method for the placement of scs in those studies , because it allowed the physician to promptly observe the patients ' perception of electrical stimulus over the range of areas with pain , followed by inducing pain relief . the scs devices used in this report have two distinct features from those of mentioned in two previous studies . eight - channel cylindrical type electrodes with the constant current system were used in this report , whereas the two prior studies used paddle type leads with constant voltage system . eight - channel cylindrical type electrodes are less invasive than the paddle type electrodes as they do not entail resection and removal of vertebral tissue . however , the paddle type electrodes have better electrical conduction properties due to larger surface contact areas and unidirectional stimulating poles , and may be associated with a lower rate of migration as compared with cylindrical type electrodes . our cases demonstrate that the cylindrical type lead can also achieve sufficient paresthesia for the intraoperative stimulation under epidural anesthesia despite its weaker conductivity than the paddle type . the constant current scs system provides a constant current flow with the change of voltage in response to impedance , while the constant voltage scs system provides constant voltage and variable current according to impedance . this is the first report on the epidural anesthesia for scs implantation using cylindrical type leads with a constant current . this report indicates the absence of a decline of paresthesia by epidural anesthesia , with no interference with the intraoperative stimulation test for the optimal placement of scs leads . although the stimulation intensity required to evoke optimal paresthesia was significantly higher than both trial tests and postoperative stimulation intensity in this report , adequate paresthesia was obtained in all patients under epidural anesthesia . this result was similar to previous reports , which proposed that the intraoperative voltage is significantly higher under epidural anesthesia because some of the superficial posterior column fibers may also be blocked by the anesthetic drugs diffusing . the local anesthetics , which are deposited into the epidural space , primarily act on the nerve roots and then completely block both the sensory and motor transmission . additionally , the local anesthetics that diffuse into the subarachnoid space do not block the spinal cord completely and only partially block transmissions in the dorsal column . intraoperative electrical stimulation test with an increased paresthesia threshold enabled positioning of the leads for scs under epidural anesthesia . because the analgesic effect was perfectly established under epidural anesthesia , patients were alert and cooperative to guide the optimal lead positioning , and it also facilitated tunneling of the lead and implantation of the pulse generator . we have experienced only minor complications , such as hypotension and bradycardia , with this anesthetic method of scs . in conclusion , this report shows that epidural anesthesia is an effective and safe method for the optimal placement of the scs to minimize the discomfort for patients without impairing patients ' response to the intraoperative stimulation test .
spinal cord stimulation ( scs ) in trials involving external stimulation are easily conducted under local anesthesia . 
 however , implantation of a permanent scs system is painful , and can be intolerable in some patients . epidural anesthesia can be used to perform the scs implantation without discomfort if the patient can localize the area of paresthesia . 
 however , little is known about epidural anesthesia for scs . this paper reports 23 cases of permanent scs with a cylindrical type lead implanted under the epidural anesthesia . 
 epidural anesthesia was sufficient in 22 patients without discomfort and significant complications . 
 the remaining patient experienced incomplete epidural anesthesia and required additional analgesics to blunt the pain . 
 all the leads were placed consistent with the patient 's report of paresthesia area under epidural anesthesia . 
 thus , epidural anesthesia is an effective and safe method for the optimal placement of scs to minimize the discomfort for patients without impairing patients ' response to the intraoperative stimulation test .