MISCELLANEOUS The Effect of Interfascial Injection on Obturator Nerve Block Compared with Nerve Stimulating Ap- proach by Ultrasound-Guide: A Randomized Clinical Trial Yong Beom Kim,1 Hee Yeon Park,1 Kyung Mi Kim,1 Hyeon Ju Shin,2 Su Bin Kim,1 Mi Geum Lee1* Purpose: This study was conducted to evaluate whether the ultrasound-guided interfascial injection technique is really compatible with the ultrasound-guided nerve stimulating technique for obturator nerve block (ONB) at the inguinal crease after bifurcation of the obturator nerve. Materials and Methods: A total 62 ONBs were performed for transurethral resection of bladder tumors under spinal anesthesia, and were divided into two groups, that is, to an ultrasound-guided ONB with nerve stimulation control group (the US-NS group) or an ultrasound-guided interfascial injection experimental group (the US-IFI group). In the US-IFI group, complete ONB was confirmed using a nerve stimulator at 5 min after completing the injection, and if residual twitching remained, another local anesthetic was injected; in such cases blocks were con- sidered to have ‘failed’. During TURB surgeries, two urology assistants determined obturator reflex grade (I-IV) at 15 min after injection completion in both groups. Results: We assumed that the US-NS group achieved complete ONB in all cases. Six cases in the US-IFI group failed to achieve complete ONB (failure rate: 0% versus 19.4%, P = .012). There was one case of grade II obturator reflex in each group. Conclusion: The ultrasound-guided interfascial injection technique was not compatible with the ultrasound-guid- ed nerve stimulating technique for ONB at the inguinal crease. Keywords: bladder tumor; nerve block; obturator nerve; transurethral resection; ultrasound INTRODUCTION Transurethral resection of bladder tumor (TURB) is an essential treatment for bladder tumors,(1) but direct electrical stimulation of the obturator nerve (ON) dur- ing TURB can trigger an inadvertent adductor muscle spasm, which can cause a serious complication like bladder perforation.(2,3) The majority of bladder cancer patients are elderly and have various comorbidities, which increase the risk of complications after general anesthesia.(4) Furthermore, even general anesthesia with muscle relaxants does not eliminate the risk of adductor muscle spasm.(2) Spinal anesthesia using a selective obturator nerve block (ONB) offers an alternative means of anesthesia for TURB, but adductor muscle spasm can be induced when ONB is incomplete.(2,3) Nerve stimulators have been used under ultrasound guidance to enhance the efficacy of ONB,(2,5,6) though recently, it has been re- ported ONB can be performed by interfascial injection under ultrasound guidance without a nerve stimulator with similar efficacies.(7,8) Basically, the ON is known to divide into two branch- es after exiting the obturator canal. The anterior branch is located in fascial planes among adductor longus, 1Department of Anesthesiology and Pain Medicine, Gil Medical Center, Gachon University College of Medicine, Incheon, Republic of Korea. 2Department of Anesthesiology and Pain Medicine, Korea University Anam Hospital, Seoul, Republic of Korea. *Correspondence: Department of Anesthesiology and Pain Medicine, Gachon University College of Medicine, Gil Medical Center, , Incheon 21565, Republic of Korea Tel: +82-32-460-3637, Fax: +82-32-469-6319, E-mail: mikeum2@gilhospital.com. Received January 2018 & Accepted September 2018 adductor brevis, and pectineus muscles, whereas the posterior branch is located between the adductor brevis and adductor magnus muscles at the inguinal crease.(7,8) Therefore, ONB has been performed using anterior and posterior branch blocks at the inguinal crease level.(4,7,8) But many clinicians are reluctant to perform ONB caused by varied anatomic locations.(9) Moreover, ON itself is very thin and generally embedded in an inter- muscular septum, so it is difficult to be found even in ultrasound image and also difficult to be electrically stimulated.(5) Therefore, we were interested in ultra- sound-guided interfascial injection, which only needs to distinguish interfascial layers, not ON, and does not need to use nerve stimulator. Since incomplete block can cause direct harm to patients, we thought that de- creasing the rate of incomplete block was important for generalization of that injection clinically. In this study, we sought to determine whether ultra- sound-guided interfascial injection is really compatible with ultrasound-nerve stimulation for TURB under spi- nal anesthesia. Urology Journal/Vol 16 No. 4/ July-August 2019/ pp. 407-411. [DOI: http://dx.doi.org/10.22037/uj.v0i0.4386] Vol 16 No 04 July-August 2019 408 MATERIALS AND METHODS Study Population Written informed consent was obtained from all pa- tients after obtaining approval from our institutional ethics committee (GAIRB2014-337) and registering in the University hospital Medical Information Network (UMIN) Clinical Trials Registry (UMIN000020534). This study was performed in accordance with the CON- SORT 2010 checklist. Inclusion and exclusion criteria Sixty-two American Society of Anesthesiologists phys- ical status (ASA) I or II patients were enrolled in the study, who underwent spinal anesthesia with ONB for elective TURB due to bladder tumors. The exclusion criteria were as follows: diabetes or peripheral neurop- athy, motor or sensory deficits in the lower extremities, ASA of III or greater, a coagulation disorder, antico- agulant medication, known allergy to local anesthetics, contraindication for spinal anesthesia (infection at in- jection site, severe scoliosis, or fusion surgery), lack of cooperation, and refusal to participate. We conducted a randomized, controlled, parallel group study (Figure 1). Written, informed consent was ob- tained on the day before the surgery. Patients were assigned into 1 of 2 groups randomly, that is, an ul- trasound-guided ONB with nerve stimulation control group (the US-NS group) or an ultrasound-guided inter- fascial injection experimental group (the US-IFI group) to receive ONB in the inguinal crease using random in- teger set generator (http://www.random.org/). The ratio of allocation was 1:1. The researcher not involved in performing the block generated the randomization set, and enrolled participants. All the performances were conducted in the operating room of Gil Medical Center, Gachon University College of Medicine, Incheon, Ko- rea, from Jan 2016 to March 2016. Procedures Routine monitoring was begun and spinal anesthesia with hyperbaric 0.5% bupivacaine 12-15 mg was ad- ministered to achieve a level of anesthesia above T 10 (at least T10 to T4) in all patients. After setting the patient in a supine position, an anes- thetic nurse who is unrelated in this study closed the curtain in front of the patient’s face to hide the proce- dure. And the patient’s affected leg was slightly abduct- ed and rotated externally without knee flexion,(9) and Figure 1. Patients’ enrollment algorithm. Figure 2. Obturator nerve block sites. The fascial planes of the adductor muscles and the pectineus muscle are identified (a). The target of anterior branch block is arrowed ①, and that of the posterior branch block is also arrowed ②. Separation of target muscles for anterior branch block (b) and posterior branch block (c) is shown. The arrowhead indicates the needle. AL, adductor longus muscle; AB, adductor brevis muscle; AM, adductor magnus muscle; P, pectineus muscle. Ultrasound-guided obturator nerve block-Lee et al. the inguinal region was prepared with a povidone io- dine solution. A 10 MHz linear probe (Zonare Medical Systems, California, USA) was equipped with a sterile plastic cover and gel, and the transducer was positioned parallel to the inguinal crease at 90° to the skin and the image depth was set at 4-5 cm. The inguinal region was examined laterally from the femoral vein until the pec- tineus muscle was identified with the adductor longus, adductor brevis, and adductor magnus medially at the inguinal crease (Figure 2a). In the US-NS group, a 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) was advanced via an ultrasound in-plane approach in a lateral to medial direction to position the needle tip at the junction of adductor longus, adductor brevis, and pectineus muscles within the fascia for an anterior branch block (Figure 2a, arrow ①). The nerve stimula- tor was then turned on, and if adductor muscle twitch- ing was observed even at 0.3 mA, 10 ml of local anes- thetic (LA; 1.5% lidocaine + epi 1:200,000) was slowly injected into the muscle interface after negative aspira- tion (Figure 2b), and then the needle was positioned at the junction of adductor brevis and adductor magnus muscles within the fascia for a posterior branch block (Figure 2a, arrow ②); 10 ml of LA was injected in the same manner (Figure 2c). If adductor muscle twitching did not occur at these locations, additional needling was performed to locate the target branch within the fascia. Transducer tilting cranially 0°-20° was also allowed if twitching did not occur with the transducer normal to skin. If LA misdistributed into muscle, the needle was redirected until the correct spread of LA was visualized. In the US-IFI group, the same amount of LA was inject- ed at anterior and posterior branch sites within fascia without a nerve stimulator. Five minutes after the main branches block,(10) the needle was re-advanced to search for residual twitching by the same anesthesiologist.(11) If twitching was still observed in both the medial aspect of thigh and the sonogram even at 0.5 mA, another 5 ml of LA was injected into the twitching site and block was documented as a failure. After the LA injection on both groups, we were able to confirm that the adductor muscle twitching disap- peared. All blocks were performed by one anesthesiolo- gist with experience of more than 60 ONBs. Evaluations The primary outcome was failure rate of ONB con- firmed with nerve stimulator only according to this study design. In the US-NS group, failure rate was as- sumed zero in all cases because we confirmed the twitch of adductor muscles was disappeared when we injected the LA. In US-IFI group, the performer blocked the first injection using only the anatomical landmark on the US image, and then blocked with nerve stimulator at the second injection for evaluating the twitches on the first injection site, the failure rate. Therefore, we made sure that the same researcher performed both injections, and made other researchers who unknown group assign- ments confirmed images, and check the success or fail- ure of ONB. It can also introduce performer bias, but different approaches were necessary in this study. The secondary outcome was the extent of adductor mo- tor block measured with obturator reflex grade. After ONB, two urologic assistants who were unaware of the group assignments entered the operating room, and patients were positioned in a lithotomy position. Neo- plasm endoscopic resection was started using a bipolar resectoscope (electrical current: 280 W) and endovesi- cal irrigation with a normal saline solution. Surgery was performed by either of six surgeons at random. We re- quested two urologic assistants to perform obturator re- flex grading 15 min after completing injection on both groups as described by Lee et al.(10): 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. Table 1. Patients’characteristics in two groups. Variables US-NS Group (N = 31) US-IFI Group (N = 31) P-value Age, year; mean ± SD 70 ± 11 68 ± 14 .461 Sex (M/F); N 25/6 25/6 .625 Height, cm; mean ± SD 166.3 ± 6.3 164.1 ± 7.6 .226 Weight, kg; mean ± SD 63.1 ± 10.2 61.9 ± 11.3 .655 ASA class (I/II); N 11/20 7/24 .201 Abbreviations: M, Male; F, Female; ASA, American Society of Anesthesiologists physical status; US-NS group, ultrasound-guided nerve stimulator group; US-IFI group, ultrasound-guided interfascial injection group. Variables US-NS Group (N = 31) US-IFI Group (N = 31) P-value Duration of surgery, min; mean ± SD 71.9 ± 40.6 69.4 ± 42.1 .807 Dose of 0.5% hyperbaric Marcaine, mg; mean ± SD 13.8 ± 1.4 13.9 ± 1.1 .762 Spinal level (T10/T8/T6/T4); N 1/3/18/9 5/4/15/7 .343 Side (Right/Left); N 15/16 17/14 .400 Failure rate; N (percentage) 0 (0)a 6 (19.4) .012b Obturator reflex grade (I/ II/ III / IV); N 30 / 1 / 0 / 0 30 / 1 / 0 / 0 Abbreviations: T, thoracic level; US-NS group, ultrasound-guided nerve stimulator group; US-IFI group, ultrasound-guided interfascial injection group. a Nerve stimulator is the only tool in confirming the complete ONB before TURB surgery. Thus, it is assumed complete ONB is achieved in all cases in the US-NS group. b Statistical significance is accepted for P values < .05. Table 2. Obturator nerve block data for the two groups. Ultrasound-guided obturator nerve block-Lee et al. Miscellaneus 409 Vol 16 No 04 July-August 2019 410 Statistical Analysis Results are presented as mean ± standard deviations, unless otherwise indicated. The statistical analysis was performed using the Statistical Package for Social Sciences software (SPSS 12.0 for Windows; SPSS Inc., Chicago, IL, USA). The Chi-squared test or the Fisher’s exact test were used to analyze categorical data (gender, ASA status, block site, spinal level, failure rate, and re- flex grade), and the Student’s unpaired t-test was used to compare continuous data (age, height, weight, sur- gery time, and marcaine doses). Statistical significance was accepted for P values < .05. In a preliminary study, success was achieved in 7 of 10 patients who underwent ultrasound-guided interfascial injection. Twenty eight blocks were required per group for an α value of 0.05 and a power of 90%, and 31 blocks were determined necessary assuming a dropout rate of 10%. RESULTS In all, 62 patients were included in the present study. Patients’ enrollment algorithm has been illustrated in Figure 1. Group demographic data are shown in Table 1, and data regarding the ONB procedure in Table 2. The number of skin punctures to ONB was one for all 62 blocks. No vascular puncture or blood aspiration occurred during procedures, and no neurologic, vascular or infection-re- lated complications were detected by follow-up urology chart reviews. Nerve stimulator was the only tool in confirming the success or failure of ONB before TURB surgery. Thus, we assumed that complete ONB was achieved in all cases in the US-NS group, and six cases in the US-IFI group failed to achieve complete ONB. One case in each group exhibited grade II obturator re- flex during the surgery, but with no other complication. No case in either group required general anesthesia to complete surgery. DISCUSSION Our results show that the ultrasound-guided interfascial injection technique is not compatible with the ultra- sound-guided nerve stimulating technique for ONB at the inguinal crease. Block was not achieved in six cases in the US-IFI group. Two types of residual twitching were found in failed cases, that is, four cases of twitch- ing on the inner part of the fascial layers beyond the area of LA spread (2 cases of anterior branch block, 2 cases of posterior branch block), and two cases of an- other form of twitching near an LA injected site when the transducer was changed slightly (1 case of anterior and posterior branch block, 1 case of anterior branch block). In this study, we decided to target fascia, not an ON,(9) which is very small and difficult to image.(2,4,5,7) ON echogenicity within fascia is not distinguishable from fascia in many cases.(9) In US-IFI group, we confirmed LA spread along the adjacent interfascial layers, not stagnating on a spot of injection. Initially, we supposed that the US-IFI group would be compatible with US-NS group, but twitching points beyond the area of LA spread were observed in some cases. It has been well-established incomplete ONB is due to inadequate LA diffusion despite a cor- rect electrical end point.(7,8) At the inguinal crease, many muscle layers are near the ON pathway, which is intertwined and complicated,(12) and thus, slight tilting of the transducer can result in missing the pathway. For example, in some cases there was no twitching when the probe was held perpendicu- lar to skin, but twitching occurred when the probe was tilted 10° cranially. Saranteas T et al. addressed the dy- namics of nerve position and found that probe angu- lations can change nerve position within the anatomic line.(13) We allowed 10-20° angulation of the probe, because high transducer angles make ONB technically difficult and increasing the risk of serious complica- tions.(2,12) Reports about anterior branch block cite success rate of more than 90%,(3,6,10) and other interfascial techniques also have been reported to have good success rates.(7,8) However, even one failed-case should be avoided be- cause of the seriousness of bladder perforation.(11) In- terfascial injection is a volumetric technique that relies on diffusion of the injected drug, and it has been shown the anterior and posterior divisions of ON have multiple branching patterns that are widely distributed among the adductor muscles.(9,10,12,13) The authors of a study show- ing the compatibility of interfascial injection approach on ONB stated that using nerve stimulator showed bet- ter accuracy in blocking the posterior branch.(7) We reapplied the nerve stimulator for searching the failed-cases of US-IFI group, and additional LA was injected for patients’ safety. Just once, stimulation of electric resectors to the bladder walls for checking the block quality can cause a strong contraction of the ad- ductor muscles and induce a bladder perforation.(7) So we used sufficiently low level of stimulant current (0.3- 0.5 mA) to confirm that the needle tip was placed as close as possible to the nerve and for the safety reasons. (11) In this study, we could not prevent obturator reflex to- tally even when complete ONB had been achieved. We tend to be nervous about even slight muscle contraction due to severity of bladder perforation, but in practical situations, operators need to be aware that even com- plete ONB does not guarantee complete adductor motor block because innervations from the femoral and sa- cral plexus also dominate contribute to adductor motor strength.(8) Definitions of complete ONB have not been stand- ardized, and in clinical situations, evaluation of ONB is time-consuming and difficult.(7,12) We assumed that complete ONB was achieved in all cases in the US-NS group, and counted failed cases in the US-IFI group, which can introduce bias. This study cannot be categorized as a double-blind study, which is one of the limitations of this study. The performers were not blinded to the group assignments (one injection for US-NS group or. two injections for US-IFI group), even though urologic assistants who evaluate obturator reflex were unaware of the group assignments because they entered the operating room after ONB. CONCLUSIONS In conclusion, the ultrasound-guided interfascial in- jection technique was not compatible with the ultra- sound-guided nerve stimulating technique for ONB at the inguinal crease, and thus, we suggest that combined use of ultrasound and nerve stimulator for ONB. Final- ly, we emphasize successful ONB does not guarantee complete adductor motor block. Ultrasound-guided obturator nerve block-Lee et al. CONFLICT OF INTEREST None declared. REFERENCES 1. Ong EL, Chan ST. Transurethral surgery and the adductor spasm. Ann Acad Med Singapore. 2000;29:259-62. 2. Moningi S, Durga P, Ramachandran G, Murthy PV, Chilumala RR. Comparison of inguinal versus classic approach for obturator nerve block in patients undergoing transurethral resection of bladder tumors under spinal anesthesia. J Anaesthesiol Clin Pharmacol. 2014;30:41-5. 3. Thallaj A, Rabah D. Efficacy of ultrasound- guided obturator nerve block in transurethral surgery. Saudi J Anaesth. 2011;5:42-4. 4. Shah NF, Sofi KP, Nengroo SH. Obturator nerve block in transurethral resection of bladder tumor: a comparison of ultrasound- guided technique versus ultrasound with nerve stimulation technique. Anesth Essays Res. 2017;11:411-5. 5. Helayel PE, da Conceicão DB, Pavei P, Knaesel JA, de Oliveira Filho GR. Ultrasound- guided obturator nerve block: a preliminary report of a case series. Reg Anesth Pain Med. 2007;32:221-6. 6. Fujiwara Y, Sato Y, Kitayama M, Shibata Y, Komatsu T, Hirota K. Obturator nerve block using ultrasound guidance. Anesth Analg. 2007;105:888-9. 7. Manassero A, Bossolasco M, Uques S, Palmisano S, De Bonis U, Coletta G. Ultrasound-guided obturator nerve block: interfascial injection versus a neurostimulation- assisted technique. Reg Anesth Pain Med. 2012;37:67-71. 8. Sinha SK, Abrams JH, Houle TT, Weller RS. Ultrasound-guided obturator nerve block: an interfascial injection approach without nerve stimulation. Reg Anesth Pain Med. 2009;34:261-4. 9. Soong J, Schafhalter-Zoppoth I, Gray AT. Sonographic imaging of the obturator nerve for regional block. Reg Anesth Pain Med. 2007;32:146-51. 10. Lee SH, Jeong CW, Lee HJ, Yoon MH, Kim WM. Ultrasound guided obturator nerve block: a single interfascial injection technique. J Anesth. 2011;25:923-6. 11. Akata T, Murakami J, Yoshinaga A. Life- threatening haemorrhage following obturator artery injury during transurethral bladder surgery: a sequel of an unsuccessful obturator nerve block. Acta Anaesthesiol Scand. 1999;43:784-8. 12. Anagnostopoulou S, Kostopanagiotou G, Paraskeuopoulos T, Chantzi C, Lolis E, Saranteas T. Anatomic variations of the obturator nerve in the inguinal region: implications in conventional and ultrasound regional anesthesia technique. Reg Anesth Pain Med. 2009;34:33-9. 13. Saranteas T, Paraskeuopoulos T, Alevizou A, et al. Identification of the obturator nerve divisions and subdivisions in the inguinal region: a study with ultrasound. Acta Anaesthesiol Scand. 2007;51:1404-6. Miscellaneus 411 Ultrasound-guided obturator nerve block-Lee et al.