2.6. Procedures
paresthesia, Pain
STERILE, PARESTHESIA, INFILTRATED
All procedure will be performed under fluoroscopic guidance. A single fluoroscopy C-arm system will be used. The patient will be placed in the prone position with a pillow under the lower abdomen. After sterile preparation of the needle insertion area, the skin will be infiltrated with 1% lidocaine, and a 22-guage, 4-in RF cannula with a 10 mm curved active tip will be advanced under fluoroscopic guidance. After appropriate positioning of the RF cannula, the stylet will be replaced by the RF probe and the probe will be connected to the PRF generator (Radiofrequency Ablation for Pain Management, G4™ RF Generator; Cosman Medical, Burlington, NJ). The final definite position of the RF probe will require a sensory stimulation (50 Hz) threshold ≤0.4 V, which create paresthesia corresponding to the existing distribution of the patient’s radicular pain. The motor stimulation threshold (2 Hz) should be more than 1.5 times greater than the sensory stimulation threshold, and impedance <400 Ω is also required. The position of the RF cannula will be slightly adjusted after each cycle of treatment, and the motor/sensory stimulation will be also performed at the same time for confirmation.In experimental high-voltage group, the output voltage will be set to 60V with temperature no more than 42°C, pulsed width of 20 millisecond, frequency at 2 Hz, and duration for 120 seconds and 3 cycles of PRF will be applied. In low-voltage group, only the output voltage will be different to 45V compared to experimental group.The generator will be manipulated by the operating room nurse, and the display will be concealed from the patient and the procedure-performing physician. After PRF, the needle will be further retreated and then repositioned at the safe triangle. After confirmation of epidural spread using a contrast dye, 1 mL of 0.3% mepivacaine will be injected.