Ultrasound-Guided ONB for Transurethral Procedures - Interadductor Approach

Overview

Obturator nerve block is an effective method to prevent adductor muscles contraction during transurethral resection of bladder tumour localized on the lateral wall. Due to prior spinal anaesthesia the patient does not feel uncomfortable during the blockade and the interadductor approach gives the possibility to perform it in the lithotomy position. The aim of the study was to evaluate the safety and effectiveness of ultrasound-guided obturator nerve identification and blockade for TURBT.

The basic methods for diagnosis and management of bladder cancer are endoscopic procedures. Transurethral resection of bladder tumor (TURBT) is usually performed under spinal anesthesia that does not prevent an unintended stimulation of the obturator nerve (ON) when electroresection is performed on the lateral wall of the bladder. This sensorimotor nerve arises from the lumbar plexus at L2-L4. It innervates the muscles responsible for adducting the thigh and the skin on the surface of the paramedian segment of the thigh. During TURBT, when the bladder has been filled with irrigation fluid, the ON is directly adjacent to the lateral wall of the bladder and it can be stimulated during the electroresection. Sudden contraction of the adductor muscles of the thigh, may lead to perforation of bladder wall with the resectoscope loop. In the Department of General, Oncologic and Functional Urology, Medical University of Warsaw approximately 500 TURBT are performed every year; 7% of them necessitate the prevention of ON stimulation. Anesthetists perform obturator nerve block (ONB) - the anterior branch, using the stimulator for the identification with the 94% efficacy. Recently, ultrasound guidance has been used to enhance the safety and efficacy of the nerve blocks that is why we have decided to evaluate the effectiveness of ONB performed with ultrasounds. An approval from the Medical University of Warsaw Bioethical Committee has been obtained. Patients need to give written informed consent to participate in the study. It is anticipated that 100 patients with TURBT performed under spinal anesthesia that, after the urologist decision, necessitate the ONB will be enrolled in this study. Before the procedure an oral premedication is given. After admission to the operating room, intravenous access is established and the patient receives a drip infusion of 500 ml 0.9% Natrium Chloratum with an antibiotic (2nd generation cephalosporin). Constant monitoring is ensured of ECG, heart rate, and pulse oxymetry. Non-invasive blood pressure measurement is taken every five minutes. To maintain patients' blood oxygenation, oxygen is delivered with the use of a facemask. Spinal anesthesia is performed with patients in the sitting position, most frequently in the L3 L4 space (in the case of technical difficulties - L2 L3 or L4 L5) using 8-15 mg 0.5% hyperbaric bupivacaine depending on the patient's anthropometric parameters. The needles used are 25-27G pencil point. After drug administration, the patient is placed in the supine position. Upon reaching the appropriate anesthesia level (Th10), which blocks conduction in the sensory nerve fibers of the bladder, the patient is placed in the lithotomy position. In the case of tumors located on the lateral wall of the bladder, the safety of TURBT is ensured using a neurotest performed by an urologist with a nerve stimulator built into the resectoscope (Neurotester FB2, ERBE). The extremity movement leads to the decision to block the ON. Ultrasound-guided ONB procedure: The patient remains in the lithotomy position. For nerve identification a linear transducer is used. It is placed next to the grain to visualize three adductor muscles. Between adductor longus and adductor brevis, in fascial plane, an anterior branch of obturator should be visualized. The needle is advanced toward the nerve in an out-of-plane trajectory. The local anesthetic is injected after heme-negative aspiration. The resistance during injection is avoided to reduce the risk of intraneural injection. If there are problems with nerve identification the anesthetic is injected in fascial plane between adductors muscles - longus and brevis. 10 ml of 2% lidocaine is used for single block and 2 x 10 ml of 2% lidocaine with epinephrine when bilateral one is needed. Before TURBT starts again, the urologist once more perform the neurotest to evaluate the ONB efficacy. After enrolling 50 patients to the study the results will be evaluated and the decision whether to decrease the amount of 10 ml of 2% lidocaine for injection will be taken.