Comparison of Nerve Stimulating Approach and Interfascial Injection Approach During Sono-guided Obturator Nerve Block
Comparison of Nerve Stimulating Approach and Interfascial Injection Approach During Sono-guided Obturator Nerve Block
Transurethral resection of bladder tumor (TURB) has been essential treatment for bladder
 tumours. Direct electrical stimulation of an obturator nerve during the TURB procedures can
 trigger an inadvertent adductor muscle spasm, which can cause a serious complication like
 bladder perforation.

 General anesthesia with muscle relaxants for TURB does not guarantee a prevention of the
 adductor muscle spasm. Spinal anesthesia with selective obturator nerve block (ONB) can be an
 alternative anesthesia for TURB, but adductor spasm can also be induced because of incomplete
 ONB. Recently, ultrasound guidance with nerve stimulator has been used to enhance the safety,
 efficacy and shortening the onset time of ONB.

 Some papers describe that comparable ONB can be done using ultrasound only without nerve
 stimulator, in which there is a principle that obturator nerve runs along a given pathway.
 Basically, obturator nerve is divided into two branches after exiting the obturator canal.
 The anterior branch is located in the fascial planes among adductor longus, adductor brevis
 and pectineus muscles, and the posterior branch is located between the adductor brevis and
 adductor magnus muscles at the inguinal area. But it has been known that there are many
 branching patterns of obturator nerve and high anatomic variability in the inguinal area in a
 cadaver study. And subdivisions of obturator nerve in the inguinal area have been described.

 Therefore, this study was conducted to investigate the success rate of ultrasound-guided
 obturator nerve block with interfascial injection approach group (US-IFI; experimental group)
 was comparable to ultrasound-guided obturator nerve block with nerve stimulating approach
 group (US-NS; control group) in TURB under spinal anesthesia. And we also evaluated adductor
 muscle twitching patterns at the inguinal region when the ONB was performed.
After obtaining approval from the Gachon Gil Hospital Ethical Committee, written informed
 consent was obtained from all patients anticipating TURB with American Society of
 Anesthesiologists physical status (ASA) I or II. Sixty two patients anticipating
 transurethral resection of the bladder tumors (TURB) under spinal anesthesia were enrolled in
 this randomized controlled trial from December 2014 to May 2015. Exclusion criteria included
 patients with diabetes or peripheral neuropathy; motor or sensory deficits in the lower
 extremities, ASA greater than III, coagulation disorders, anticoagulant medication, known
 allergy to local anesthetics, contraindications for spinal anesthesia (infection at injection
 site, severe scoliosis or fusion operation), uncooperative patients and patients' refusal.
 Routine monitoring was begun and Spinal anesthesia with hyperbaric 0.5% bupivacaine 12-15 mg
 was performed to reach the level of anesthesia, at least T10 to T4 in all patients.

 Patients were then randomized into 1 of 2 groups (US-NS vs US-IFI) to receive ONB in the
 inguinal crease level. Randomization was performed by a computer-generated random numbers
 table. We counted one side obturator nerve as one, the number. Whether the right or left ONB
 was done, was decided by surgeon according to the tumor location. If obturator block was done
 in both sides, let it belong to the same group, and we counted it as two, the number.

 Patients were then positioned supine, and the affected leg was slightly abducted and rotated
 externally without knee flexion, and the inguinal region was prepared with a povidone iodine
 solution. The 10 MHz linear probe (Zonare Medical Systems, California, USA) equipped with a
 sterile plastic cover and gel. The transducer was positioned parallel to the inguinal crease
 with 90° to the skin with the image depth of 4-5 cm. The inguinal region was examined
 laterally from the femoral vein until the 3 muscle layers consisting of the adductor longus,
 adductor brevis, and adductor magnus were identified with pectineus muscle medially along the
 inguinal crease. We allowed transducer tilting cranially 0°-20° angle until a fascial planes
 of the pectineus and adductor muscles were identified. A thick hyperechoic fascia was used as
 a targeting landmark for ONB, not focus on the obturator nerve itself (One between adductor
 longus and adductor brevis muscles for anterior branch, another between adductor brevis and
 adductor magnus muscles for posterior branch of obturator nerve). We excluded the case, in
 which three muscle layers were not identified definitely within the range.

 In the US-NS group, 22-gauge, 120-mm stimulating needle (Stimuplex insulated needle; D Plus
 B. Braun, Melsungen, Germany) attached to a nerve stimulator (Stimuplex HNS12;B. Braun,
 Melsungen, Germany) advanced via an ultrasound in-plane approach from lateral to medical
 direction to position the needle tip on the anterior branch. The nerve stimulator was then
 turned on, and the stimulation current started at 0.5 mA. If adductor muscle twitching was
 observed on the sonogram even at the stimulation current 0.3mA, 10mL of local anesthetics
 (LA; 1.5% lidocaine + epi 1:200,000) were slowly injected within the muscle interface after
 negative aspiration, resulting in separation of these two muscles under real-time
 visualization. If there was misdistribution of LA spread (eg, spread into the muscle tissue),
 the needle was redirected until the correct spread of LA was visualized. The needle was
 withdrawn to the skin and reinserted to position the needle tip on the posterior branch. The
 stimulation current started at 0.5 mA. If adductor muscle twitching was visualized on the
 sonogram even at 0.3mA, another 5mL of LA was injected. After injection to the anterior and
 posterior branch, the stimulation current increased 1.0 mA, and needle was re-advanced as
 like Fig 1d for searching the residual muscle twitching. If muscle twitching was observed,
 then current was decreased to 0.5 mA, and confirming the muscle twitching on the sonogram at
 that current, 5ml of LA injected. We wrote that muscle twitching was occurred in what kind of
 muscles or fascias.

 In the US-IFI group, 22-gauge, 120-mm stimulating needle (Stimuplex insulated needle; D Plus
 B. Braun, Melsungen, Germany) without nerve stimulator advanced via an ultrasound in-plane
 approach from lateral to medical direction to position the needle tip on anterior branch.
 After negative aspiration, 10mL of LA were slowly injected within the muscle interface,
 resulting in separation of these two muscles under real-time visualization. The needle was
 withdrawn to the skin and reinserted to position the needle tip on posterior branch, another
 5mL of LA was injected. After that, the needle was withdrawn to the skin and reinserted to
 the same spots, attached with nerve stimulator at the stimulation current 1.0 mA for
 confirming the block of anterior and posterior branch. If adductor muscle twitching was shown
 on sonogram, another 5mL of LA was injected, and it was documented as 'fail'. After that,
 needle was re-advanced as like US-NS group for searching the residual muscle twitching. It
 then went through the same process as the US-NS group, and we wrote that muscle twitching was
 occurred in what kind of muscles or fascias. We used only the nerve stimulator for confirming
 the success or fail of the ONB before the TURB surgery.

 Any needle redirection after withdrawing to the skin, was recorded as an additional needle
 pass. Before the injection, the image was captured as static, and the depth of anterior and
 posterior branch was measured by use of the built-in caliper of the ultrasound machine. We
 recorded ONB time, and time from the start of the sonographic examination until muscle layers
 identification was included. All blocks were performed by one anesthesiologist with more than
 60 ONB experiences.

 After performing the ONB, patients were positioned in lithotomy position. Endoscopic
 resection of the neoplasm was started using a bipolar resectoscope (electrical current: 280
 W) and endovesical irrigation with a normal saline solution. The surgery was performed by six
 surgeons randomly. We requested two assistants of urology, who didn't know the study groups
 (US-NS vs US-IFI) for obturator reflex grading. Obturator reflex grade was assessed by the
 scale of Lee's paper. Gr I: no movement or palpable muscle twitching, Gr II: palpable muscle
 twitching without movement, Gr III: slight movement of the thigh not interfering with the
 surgical procedure, and Gr IV: vigorous movement interfering with the surgical procedure.
Inclusion Criteria:

 -  all patients anticipating transurethral resection of bladder tumors with American
 Society of Anesthesiologists physical status(ASA) I or II

 Exclusion Criteria:

 -  patients with diabetes or peripheral neuropathy; motor or sensory deficits in the
 lower extremities, ASA greater than III, coagulation disorders, anticoagulant
 medication, known allergy to local anesthetics, contraindications for spinal
 anesthesia (infection at injection site, severe scoliosis or fusion operation),
 uncooperative patients and patients' refusal