Electrical stimulation of the epiradicular space using a catheter with a removable stylet

BACKGROUND: Electrical stimulation can be used to verify the location of epidural catheters. Although epiradicular localization of a catheter is important for patients with radiating pain in the lower extremities due to spinal stenosis or disc herniation, no prospective study results pertaining to the stimulation threshold within the epiradicular space have been reported. Therefore, we set out to investigate the threshold current for motor response in the epiradicular space by the use of a catheter containing a removable stylet. In addition, this study examines the reliability of such epiradicular stimulation. METHODS: In 105 patients undergoing a retrograde interlaminar ventral epidural injection, a lumbar epiradicular catheter was inserted. Loss of resistance was used to identify the epidural space. Afterward, the TheraCath was advanced into the epiradicular space and connected to a nerve stimulator. A nerve stimulator delivered progressively, increasing electrical current until an appropriate muscle contraction was observed. Contrast media was then injected and epiradicular dispersal was assessed. RESULTS: Epiradicular stimulation yielded a mean threshold of 0.56 +/- 0.50 mA (range: 0.06 to 2.84). When compared with epiradicular dispersal as a gold standard, the sensitivity, specificity, positive predictive value, and negative predictive value of epiradicular stimulation with the TheraCath were 90%, 56%, 96% and 33%, respectively. CONCLUSIONS: The threshold current of an insulated needle required to elicit a motor response in the epiradicular space was evaluated. We conclude that the epiradicular stimulation test is useful for confirming catheter placement. Nonetheless, further studies are required before implementing its routine use in clinical settings.

Minimum current requirement for confirming the localization of an epiradicular catheter placement / 대한마취과학회지

BACKGROUND: Based on the necessity to confirm the epiradicular catheter misplacement, epiradicular threshold current for the confirmation of catheter tip localization is required. METHODS: Thirty-four adult patients with low extremity radiating pain were to receive epiradicular catheterization at the lumbosacral level. The epidural space was accessed percutaneously in cranial to caudal direction. A metal coil-reinforced epidural catheter was inserted and advanced caudolaterally toward the target neural foramen until the catheter tip was located below the bisection of pedicle. The electrical stimulation was performed after catheter placement in epidural and epiradicular space. Using the constant current nerve stimulator, the stimulating current was increased from 0 to 5 mA (pulse width of 0.3 ms; frequency of 2 Hz) until adequate motor contraction was evident. The threshold current for motor response with epidural space (EDmA) and epiradicular space (ERmA) placement were recorded upon electrical stimulation. In addition, the threshold charge for motor response with epidural (EDnC) and epiradicular (ERnC) placement were recorded. RESULTS: Of 34 catheters intentionally placed in the epiradicular space, ERmA was 0.53 +/- 0.48 mA. The ERnC was significantly lower than EDnC (P < 0.05). The EDmA and ERmA were below 1 mA in 3 patients and above 1 mA in 4 patients, respectively. CONCLUSIONS: We conclude that, threshold current for motor response seems to be lower for epiradicular compared with epidural placement, although we were not able to directly investigate the epidural threshold current. The threshold current of epiradicular space overlap that in the epidural space.