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 Table of Contents  
Year : 2019  |  Volume : 33  |  Issue : 3  |  Page : 151-155

Randomized trial comparing the incidence of unintended sciatic nerve block following ultrasound-guided pudendal nerve block with two different volumes of ropivacaine for hemorrhoidectomy: A pilot study

1 Department of Anaesthesiology, Sree Balaji Medical College, Chennai, India
2 Department of Anaesthesiology, Shri Sathya Sai Medical College, Kancheepuram, Tamil Nadu, India
3 Department of Microbiology, Sree Balaji Medical College, Chennai, India

Date of Submission22-Aug-2019
Date of Decision03-Oct-2019
Date of Acceptance28-Oct-2019
Date of Web Publication5-Dec-2019

Correspondence Address:
Prof. Krishnagopal Vinod
No. 4/32, Second Main Road, M.G.R. Nagar, Velachery, Chennai - 600 042, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijpn.ijpn_60_19

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Aim: To compare the incidence of unintended sciatic nerve block following pudendal nerve block in the interligamentous plane with two different volumes of ropivacaine for post hemorrhoidectomy pain. Materials and Methods: 30 patients undergoing hemorrhoidectomy were enrolled for the study and randomly divided into two groups. Prior to the block a scout scan was performed and the pudendal artery, nerve and the sciatic nerve were identified in the interligamentous plane. All the patients received bilateral pudendal nerve block under ultrasound guidance with 5ml of 0.25% ropivacaine in group 1 and 10 ml in group 2. The spread of local anaesthetic to the ipsilateral sciatic nerve was noted under ultrasound imaging. The time of first rescue analgesia (FRA) and total analgesic requirement(TAR) were noted in both groups. The overall patient satisfaction was assessed with a three point scale.The unintended motor and sensory block of the sciatic nerve was noted. Results: The right pudendal artery was visualized in all cases where but left pudendal artery was not visualized in 1 case. The right & left pudendal nerve was visualized in 40% & 46.7% of cases in group I and 40% in both sides of group 2. The incidence of spread of drug towards the right and left sciatic nerve was more in group II (73.3% & 66.6%) than group I (40% & 33.3%). Statistically significant difference was not noted in the time for FRA (P value 0.684) & TAR (P value 0.579). There was no clinically significant sciatic nerve block. Conclusion: We conclude that less volume of local anaesthetic can achieve effective pudendal nerve block minimizing the spread to ipsilateral sciatic nerve.

Keywords: Interligamentous plane, pudendal nerve block, ropivacaine

How to cite this article:
Vinod K, Kurhekar P, Sharanya K. Randomized trial comparing the incidence of unintended sciatic nerve block following ultrasound-guided pudendal nerve block with two different volumes of ropivacaine for hemorrhoidectomy: A pilot study. Indian J Pain 2019;33:151-5

How to cite this URL:
Vinod K, Kurhekar P, Sharanya K. Randomized trial comparing the incidence of unintended sciatic nerve block following ultrasound-guided pudendal nerve block with two different volumes of ropivacaine for hemorrhoidectomy: A pilot study. Indian J Pain [serial online] 2019 [cited 2020 Sep 23];33:151-5. Available from: http://www.indianjpain.org/text.asp?2019/33/3/151/272385

  Introduction Top

Hemorrhoidal disease is the most common anorectal disease which is best treated by surgical resection as it relieves symptoms and provides a good quality of life.[1] Posthemorrhoidectomy pain can be severe leading to urinary retention, constipation, and readmission following day-care surgery.[2],[3] Multiple pain relief techniques such as topical application and local infiltration are in practice. In some cases, pain can be difficult to control effectively even after the use of parenteral nonsteroidal anti-inflammatory agents and opioids.[2],[4] The inferior rectal nerve is a branch of the pudendal nerve (PN) which carries sensations from the lower anal canal and perianal skin. Blockade of PN can help in controlling posthemorrhoidectomy pain. A previous study has shown that PN block with local anesthetic (LA) agent reduces postoperative opioid requirement and systemic complications such as urinary retention.[5] PN is formed by anterior division of S2, S3, and S4, and it passes through the greater sciatic foramen below the piriformis muscle. Subsequently, it passes between the sacrotuberous and the sacrospinous ligaments and then enters pudendal canal/Alcock's canal, where it gives rise to inferior rectal nerve. PN can be blocked in the interligamentous plane or in the Alcock's canal under the guidance of nerve stimulator, fluoroscopy, or ultrasonogram (USG). USG is more advantageous than fluoroscopy and nerve stimulator as it is devoid of radiation, is less cumbersome, gives clear delineation of soft tissues/nerves/blood vessels, and avoids nerve injury. The identification of interligamentous plane and assessment of spread of injectate surrounding the nerve can only be done under USG guidance.[6] Previous studies on PN blockade for posthemorrhoidectomy pain were done with the help of nerve stimulator at the Alcock's canal.[5],[7] USG-guided interligamentous approach is better than Alcock's canal approach for three reasons: (1) interligamentous approach has better success rate, (2) in the Alcock's canal, USG cannot identify the needle accurately,[8],[9] and (3) anatomical variations of PN can lead to branching of the inferior rectal nerve before its entry into the Alcock's canal, thus causing inadequate analgesia.[10] However, the main drawback of interligamentous approach is the proximity of the PN to the sciatic nerve (SN). Blockade of PN in the interligamentous plane can result in unintended SN blockade. The data regarding USG-guided PN block were very limited. Those studies were done to treat chronic pain conditions of the PN with 4 mL of LAs. Studies regarding USG-guided PN block for acute pain relief were not available. The minimum effective volume of LA needed to block PN in the interligamentous plane without SN blockade is not known.

We hypothesized that a small volume of LA used to block PN under USG would not spread to SN. The aim of the study was to evaluate the incidence of unintended block of SN following the bilateral PN block with two different volumes of 0.25 ropivacaine for posthemorrhoidectomy pain.

  Subjects and Methods Top

This was a prospective randomized double-blinded study conducted over a period of 9 months (February 2017–December 2017). Thirty patients undergoing elective hemorrhoidectomy who showed a willingness to participate in the study were enrolled after obtaining approval from the institutional ethical committee. Patients aged between 18 and 60 years, belonging to the American Society of Anesthesiologists Physical Status I and II, posted for elective hemorrhoidectomy were included in the study. Patients suffering from psychiatric illness, coagulation disorder, and neuropathic illness were excluded from the study.

The postoperative pain relief options were explained to the patients, and written informed consent regarding PN block and inclusion in the study was obtained from the patients. All the patients fasted for 6 h preoperatively. The patients were randomly divided into two groups by list of computer-generated random numbers. Group I received 5 mL of 0.25% ropivacaine (2.5 mL of 0.5% ropivacaine diluted with 2.5 mL of normal saline) (Ropin, 0.5%, Neon laboratories, India) in the interligamentous plane on each side. Group II received 10 mL of 0.25% ropivacaine (5 mL of 0.5% ropivacaine diluted with 5 mL saline) for PN block in the interligamentous plane on each side. Motor power of the SN was assessed before giving the block by dorsiflexion and plantar flexion of both the lower limbs. Intravenous access was obtained with an 18G cannula, and a bolus 5 mL/kg of lactated Ringer's solution was administered. Heart rate, electrocardiogram, noninvasive blood pressure, and pulse oximeter (SpO2) monitors were connected and monitored continuously. All the patients were administered glycopyrrolate 0.2 mg and fentanyl 2 μg/kg intravenously.

The patients were placed in prone position. For patients belonging to Group I, bilateral ultrasound (Philips ClearVue 650)-guided PN block was given using a low-frequency probe (3–6 MHz). Under strict aseptic precaution, the probe was covered in a sterile sleeve and was placed transversely over the posterior superior iliac spine. The probe was moved laterally to visualize the ilium [Figure 1], which was visualized as a hyperechoic line descending diagonally across the superomedial to inferolateral corner of the screen. After visualizing the ilium, the probe was moved caudally until the piriformis muscle and the greater sciatic notch were visualized [Figure 2]. The probe was moved further caudally till the disappearance of the piriformis muscle and appearance of the ischial spine (IS) as a straight hyperechoic line. Sacrospinous and sacrotuberous ligaments were identified. Medial to the IS, in between the ligaments, the internal pudendal artery (PA) and the PN were identified. The probe was moved laterally to identify the SN [Figure 3]. A 22G 10-cm needle was inserted medial to the probe and advanced under USG guidance until the sacrotuberous ligament was pierced which was appreciated as a pop off in the advancing hand. A small volume (0.5 mL) of saline was injected to confirm the position of needle, medial to the artery in the interligamentous plane.[11] Five milliliters of 0.25% ropivacaine was injected incrementally after repeated aspiration. The block was repeated on the opposite side. The identification of PA and nerve on both sides was noted. The spread of LA in the interligamentous plane and to the SN was noted on both sides. For patients belonging to Group II, the same procedure was followed with 10 mL of 0.25% ropivacaine on each side. Following the block, the patients were turned to supine position, and general anesthesia was induced with propofol 2 mg/kg and atracurium 0.5 mg/kg IV. Airway was secured with appropriate size laryngeal mask airway and ventilated with oxygen, nitrous oxide, and volatile anesthetics. At the end of the procedure, the patients were reversed and extubated. Following extubation, the patients were observed in the recovery room, and the following parameters were monitored.
Figure 1: Ileum

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Figure 2: Greater sciatic notch

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Figure 3: Pudendal nerve, pudendal nerve, ischial spine, and sciatic nerve

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The primary outcome of the study was to compare the incidence of unintended SN block between the two groups. The secondary outcomes of the study were to compare the spread of LA to SN, duration of analgesia, and total analgesic requirement.

Time of completion of block was taken as time zero. Time of first analgesic requirement was calculated in minutes from time zero to the point where patient receives rescue analgesics following first complaint of pain. Injection tramadol 2 mg/kg, intramuscular was given as rescue analgesia on demand. The total demand of analgesics in 24 h was noted. Following the injection, the patients were assessed at the 4th hourly interval for 24 h. Patients' satisfaction was assessed by a three-point scale excellent, satisfactory, and unsatisfactory.[7] SN block was assessed by pinprick with a blunt needle in the sole of foot and weakness on dorsiflexion and plantar flexion of the foot.

Statistical analysis

The statistical analysis was done using the Statistical Package for the Social Sciences for Windows (Microsoft USA), version 23, Armonk, NY, USA: IBM corporation and its licensors 2015. The distribution of data was analyzed with Kolmogorov–Smirnov test. Demographic characteristics were analyzed with Student's t-test, and data were expressed as mean ± standard deviation. Time of the first rescue analgesia (FRA) and total analgesic requirement were analyzed with Mann–Whitney U-test and were expressed as median ± standard error of the mean. The identification of PA and nerve, spread of LA, and blockade of SN were compared with Chi-square test and were expressed as number and percentage. P < 0.05 was considered as statistically significant for two-sided test.

  Results Top

Demographic characteristics [Table 1] were similar between the two groups. FRA was slightly more in Group I (710 ± 101.69 min) than Group II (653 ± 94.70 min), but it was not statistically significant (P = 0.684) [Table 1]. Total analgesic requirement was comparable between the two groups but was slightly lesser in Group I (0.93 ± 0.15) than Group II (1.06 ± 0.15), but the difference was not significant (P = 0.579) [Table 1].
Table 1: Patients' characteristics, analgesic duration, and requirement

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The right internal PA was visualized in all the cases in both the groups. The left internal PA was not visualized in one case belonging to Group I. The right and left PNs were visualized in 40% and 46.7% of the cases in Group I and 40% on both sides in Group II, respectively [Table 2]. The right SN (RT SN) and left SN (LT SN) were seen in all the patients in each group. The incidence of spread of drug toward the RT SN was more in Group II (73.3%) than Group I (40%) (P = 0.06) [Table 2]. The incidence of spread of drug toward the LT SN was more in Group II (66.6%) than Group I (33.3%) (P = 0.06) [Table 2]. There was no incidence of motor or sensory block in the RT SN and LT SN in either group [Table 2]. Overall patient satisfaction was similar in both the groups [Table 2].
Table 2: Ultrasound findings

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  Discussion Top

The incidence of unintended SN block following the PN block in the interligamentous plane was found to be zero in our study. Although there was a spread of drug toward the SN (40% and 33.3% in the 5-mL group vs. 73.3% and 66.6% in the 10-mL group), no clinically significant motor or sensory block was recorded. Duration of analgesia and total analgesic requirement were comparable between the groups.

In previous studies, 4–5 mL of LA was used for blocking PN in the interligamentous plane. Although this volume was sufficient to produce clinical analgesia, it was thought to be too much for interligamentous space and subsequently resulting in SN blockade. It was also observed that 80% of the injectate spreads to the surrounding tissue and only 20% remains in the interligamentous plane. Even though the spread of LA surrounding SN was observed, only a few studies have reported the clinical evidence of sciatic blockade.

In the study conducted by Bellingham et al., the volume of drug injected was 4 mL of 0.5% bupivacaine with 40 mg of Depo-medrol and the spread to the sacral and SN was 21.7%.[12] Rofaeel et al. studied the accuracy of USG for PN block in 17 patients with pudendal neuralgia. The total volume of injectate used was 6–7 mL (1–2 mL of 5% dextrose, 5 mL of 0.25% bupivacaine, and 40 mg of Depo-Medrol). The spread of injectate between the ligaments was seen in 88% of the patients. Even though the spread of injectate to SN was seen in 88% of the patients, the clinical signs of sciatic blockade were seen in only one patient manifesting as foot drop.[6] In our study, we found that the spread of LA to SN was seen in 70% of the patients on the right side and 66% of the patients on the left side in Group I. This difference was significantly more than 5 mL of the injectate group, but no patient in either group showed any sign of SN blockade. Wang et al. studied the spread of injectate by injecting 4 mL of dye in the interligamentous plane, just medial to the ischial spine. They found that the spread of injectate in the interligamentous plane is unpredictable, and one of four injectate spreads was to the gluteus maximus and piriformis muscle which may cause unintended SN block.[13] In our study, there was an unintended spread of LA to SN in 30% of the patients with 5 mL of injectate, but it did not lead to clinical manifestation of SN blockade. In the study conducted by Vancaillie et al., the PN block was administered transrectally with 5 mL of 0.5% levobupivacaine. They found complete pain relief for 64 h. Complications including temporary numbness of the lower limb were seen in 7 of 66 patients, which could be due to lithotomy position and not because of sacral spread of the drug.[14] In our study, the duration of analgesia was around 10 h with 5 mL of 0.25% ropivacaine, and no patient had SN blockade. Bendtsen et al. performed PN block in the Alcock's canal with 10 mL of 0.5% ropivacaine in three patients with chronic pain and concluded that even 10 mL of LA did not cause SN block.[15] In one of the case series on PN block in patients undergoing urethroplasty, one among the three patients had weakness and loss of sensation of the right lower limb. The authors used 15 mL of 0.5% ropivacaine and concluded that the weakness and loss of sensation were attributed to compression neuropathy due to prolonged lithotomy and not due to LA spread to SN.[16]

The PN was visualized in both the groups in about 40%–46.6% of the patients. Roefeel et al. could not visualize the PN in 12% of the patients. Gruber et al. have mentioned about the difficulty in visualization of PN under US due to its small diameter (0.6–6.8 mm).[17]

FRA in our study was 710 ± 101.69 min in Group I and 653 ± 94.70 min in Group II. In the pilot study conducted by Imbelloni et al. in the year 2005 using 0.25% S75:R25 bupivacaine (20 mL on each side), the mean duration of analgesia was 23.77 h. In the comparative study done by Imbelloni in the year 2007, the mean duration of analgesia was 23.8 ± 4.8 h with bupivacaine and 3.6 ± 1 h in the control group. The major cause of pain or discomfort in our patients was because of the anal plug kept by the surgeon. It was a routine protocol to place the plug for the first 24 h.

In the study conducted by Rouholamin et al. on preemptive PN block, mean morphine consumption was less at 4 and 12 h following the block in the test group when compared to the control group.[18] Hence, analgesia following the pudendal block persisted for 12 h which was similar to our study.

The clinically significant blockade of SN needs two or three smaller aliquots at different locations around the nerve.[19] Liu et al. have concluded that minimum 13 mL of 0.5% ropivacaine injected in the perineural area results in successful SN block.[20]

There were some limitations in our study: (1) this was a pilot study (sample size: 30) and (2) placement of the anal plug prevented us from calculating the exact duration of postoperative analgesia, as it caused a vague pain due to distention.

  Conclusion Top

We conclude that in both the groups (5 mL or 10 mL) following the PN block in the interligamentous plane, there was a spread of LA toward the SN evident in the USG, but there was no clinically demonstrable motor or sensory blockade of the SN.

Financial support and sponsorship

This study was financially supported by Shri Sathya Sai Medical College and Research Institute, Kancheepuram, Tamil Nadu, India.

Conflicts of interest

There are no conflicts of interest.

  References Top

Riss S, Weiser FA, Schwameis K, Riss T, Mittlböck M, Steiner G, et al. The prevalence of hemorrhoids in adults. Int J Colorectal Dis 2012;27:215-20.  Back to cited text no. 1
Medina-Gallardo A, Curbelo-Peña Y, De Castro X, Roura-Poch P, Roca-Closa J, De Caralt-Mestres E. Is the severe pain after Milligan-Morgan hemorrhoidectomy still currently remaining a major postoperative problem despite being one of the oldest surgical techniques described? A case series of 117 consecutive patients. Int J Surg Case Rep 2017;30:73-5.  Back to cited text no. 2
Gerbershagen HJ, Aduckathil S, van Wijck AJ, Peelen LM, Kalkman CJ, Meissner W. Pain intensity on the first day after surgery: A prospective cohort study comparing 179 surgical procedures. Anesthesiology 2013;118:934-44.  Back to cited text no. 3
Okuş A. Local pain-reducing methods after hemorrhoidectomy. World J Surg 2013;37:2007-8.  Back to cited text no. 4
Imbelloni LE, Vieira EM, Gouveia MA, Netinho JG, Spirandelli LD, Cordeiro JA, et al. Pudendal block with bupivacaine for postoperative pain relief. Dis Colon Rectum 2007;50:1656-61.  Back to cited text no. 5
Rofaeel A, Peng P, Louis I, Chan V. Feasibility of real-time ultrasound for pudendal nerve block in patients with chronic perineal pain. Reg Anesth Pain Med 2008;33:139-45.  Back to cited text no. 6
Imbelloni LE, Vieira EM, Carneiro AF. Postoperative analgesia for hemorrhoidectomy with bilateral pudendal blockade on an ambulatory patient: A controlled study. J Coloproctol 2012;32:291-6.  Back to cited text no. 7
Rojas-Gómez MF, Blanco-Dávila R, Tobar Roa V, Gómez González AM, Ortiz Zableh AM, Ortiz Azuero A. Regional anesthesia guided by ultrasound in the pudendal nerve territory. Rev Colomb Anestesiol 2017;45:200-9.  Back to cited text no. 8
Pen PH, Chan CW. Ultrasound guided blocks for pelvic pain. In: Narouze SN, editor. Atlas of Ultrasound Guided Procedures in Interventional Pain Management. New York, NY, USA: Springer; 2011. p. 219.  Back to cited text no. 9
Schraffordt SE, Tjandra JJ, Eizenberg N, Dwyer PL. Anatomy of the pudendal nerve and its terminal branches: A cadaver study. ANZ J Surg 2004;74:23-6.  Back to cited text no. 10
Peng P, Narouze S. Ultrasound-guided interventional procedures in pain a medicine: A review of anatomy, sonoanatomy and procedures. Part 1 non axial structures. Reg Anesth Pain Med 2008;33:139-45.  Back to cited text no. 11
Bellingham GA, Bhatia A, Chan CW, Peng PW. Randomized controlled trial comparing pudendal nerve block under ultrasound and fluoroscopic guidance. Reg Anesth Pain Med 2012;37:262-6.  Back to cited text no. 12
American Academy of Pain Medicine. Ultrasound Guided Pudendal Nerve Block: A Cadaveric Study. ScienceDaily; 2014. Available from: http://www.sciencedaily.com/releases/2014/03/140306211036.htm. [Last accessed 2017 Dec 20].  Back to cited text no. 13
Vancaillie T, Eggermont J, Armstrong G, Jarvis S, Liu J, Beg N. Response to pudendal nerve block in women with pudendal neuralgia. Pain Med 2012;13:596-603.  Back to cited text no. 14
Bendtsen TF, Parras T, Moriggl B, Chan V, Lundby L, Buntzen S, et al. Ultrasound-guided pudendal nerve block at the entrance of the pudendal (Alcock) canal: Description of anatomy and clinical technique. Reg Anesth Pain Med 2016;41:140-5.  Back to cited text no. 15
Kalava A, Pribish AM, Wiegand LR. Pudendal nerve blocks in men undergoing urethroplasty: A case series. Rom J Anaesth Intensive Care 2017;24:159-62.  Back to cited text no. 16
Gruber H, Kovacs P, Piegger J, Brenner E. New, simple, ultrasound-guided infiltration of the pudendal nerve: Topographic basics. Dis Colon Rectum 2001;44:1376-80.  Back to cited text no. 17
Rouholamin S, Jabalameli M, Mostafa A. The effect of preemptive pudendal nerve block on pain after anterior and posterior vaginal repair. Adv Biomed Res 2015;4:153.  Back to cited text no. 18
[PUBMED]  [Full text]  
Atchabahain A, Vandepitte C, Lopez AM, Lin JA. Ultrasound-guided sciatic nerve block. Hadzic's Textbook of Regional Anaesthesia and Acute Pain Management. 2nd ed. New York: McGraw Hill; 2017. p. 620-8.  Back to cited text no. 19
Liu Z, Xiang M, Luo N, Li S, Huang S, Zhu W, et al. Minimum effective anaesthetic volume of ropivacaine 0.5% for sciatic nerve block in arthroscopic knee surgeries. J Anesth Res Pain Med 2017;2:41-7.  Back to cited text no. 20


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  [Table 1], [Table 2]


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