Journal of Midwifery & Women’s Health
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Clinical Rounds
Pudendal Nerve Block for Vaginal Birth Deborah Anderson, CNM, MSN, IBCLC
CEU
Pudendal nerve block is a safe and effective pain relief method for vaginal birth. Providing analgesia to the vulva and anus, it is used for operative vaginal birth and subsequent repair, late second stage pain relief with spontaneous vaginal birth, repair of complex lacerations, or repair of lacerations in women who are unable to achieve adequate or satisfactory pain relief during perineal repair with local anesthesia. Key to its efficacy is the knowledge of pudendal nerve anatomy, the optimal point of infiltration of local anesthetic, and an understanding of the amount of time necessary to effect adequate analgesia. c 2014 by the American College of Nurse-Midwives. J Midwifery Womens Health 2014;59:651–659 Keywords: pudendal nerve block, local anesthetics, labor analgesia, labor anesthesia, labor pain management
CASE REPORT
K.S. is a 29-year old nulliparous woman at 39 weeks’ gestation who presented to a labor and delivery unit with a 3-day history of irregular, painful contractions accompanied by an inability to sleep for the previous 2 nights. Her cervical examination was unchanged (2 cm dilated, 80% effaced, -3 station, and posterior) from her previous examination 24 hours earlier. She had a normal antepartum course, her vital signs were normal, the estimated fetal weight was 3300 g, and the fetal heart rate was Category 1. K.S. was admitted for therapeutic rest, and after obtaining her consent, she was given 15 mg of intramuscular morphine sulfate and 25 mg of intramuscular hydroxyzine (Vistaril). She slept for 6 hours and awoke with regular contractions, and her cervical examination was 4 cm dilated, 90% effaced, -3 station. K.S.’s labor then progressed normally through the active phase. She chose nonpharmacologic methods of pain relief to help her work with the pain of labor. During the second stage, her fetus rotated from right occiput posterior to right occiput anterior position. Three hours after the second stage started, the fetus was at a +3 station but had made no descent over the course of the previous hour. K.S. reported exhaustion and an inability to push, and despite continuous supportive guidance, position change, rest, adequate hydration, and frequent strong contractions, she was making little pushing effort. At that point, she was unable to push further and asked for assistance with the birth. The fetal heart rate throughout labor was Category 2, at 150 bpm, moderate variability, and occasional mild to moderate variable decelerations. Given evidence of maternal exhaustion and her request for assistance, the consulting physician was contacted, and the midwife and consulting physician reviewed with K.S. the option of continued pushing efforts or vacuum-assisted birth with anesthesia. She elected to go forward with a vacuum-assisted birth and pudendal nerve block. The risks and benefits of vacuumassisted vaginal birth and pudendal nerve block were reviewed, and she consented.
A pudendal nerve block was placed bilaterally with 1% lidocaine (Xylocaine), 10mL (100mg). Twenty minutes following placement of the pudendal nerve block, adequate anesthesia was achieved, and a vacuum-assisted vaginal birth was performed. K.S. sustained a second-degree perineal laceration that was repaired with analgesia provided by the continuing pudendal nerve block. Her postpartum course was uneventful, and she was discharged home with her newborn 2 days later. INTRODUCTION
Address correspondence to Deborah Anderson, CNM, MSN, IBCLC. E-mail: [email protected]
Second-stage labor pain originates from the increasing distention of the vagina, vulva, and perineum.1 Pain impulses travel via the sensory and motor fibers of the bilateral pudendal nerves, which are the primary source of sensory innervation to the lower vagina, vulva, perineum, and anus. The pudendal nerve also provides motor innervation to the perineal muscles, urethral sphincter, and external anal sphincter.2 Infiltration of local anesthesia around the trunk of the pudendal nerve inhibits nerve transmission and provides safe and effective pain relief for vaginal birth.3,4 In obstetrics, pudendal nerve block is primarily used to achieve analgesia for operative vaginal birth and/or repair of genital tract lacerations1,5 although it may also be used for second stage pain relief for women who are close to having a spontaneous vaginal birth. Pudendal nerve block may also be initiated for women who do not have adequate or satisfactory pain relief during perineal repair following instillation of local anesthesia to the perineum. Prior to the widespread use of epidural anesthesia in obstetrics, pudendal nerve block was a commonly used anesthesia technique for vaginal birth.6 Reported as early as 19087 pudendal nerve block became popular in the mid-1950s4 and was an often used anesthesia for childbirth into the mid1980s. As epidural use grew in popularity, pudendal nerve block declined in the United States. An estimated 5% to 10% of parturients received pudendal nerve block in the mid1990s.8 Similarly, use of pudendal nerve block in Sweden declined from 50% in the 1970s to 4% in recent years.9 A 2004 study from Italy cited pudendal nerve block as the anesthetic procedure most commonly used in Europe when no
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analgesia was requested by parturients or in hospitals without a service for obstetric analgesia.10 There are no published surveys addressing current obstetric use of pudendal nerve block in the United States. Effectiveness of Pudendal Nerve Block
Because the bearing down reflex may be blocked following pudendal anesthesia, second stage pudendal nerve block is usually administered immediately before birth.5 Older studies from Sweden11,12 report use of pudendal nerve block throughout the second stage, just prior to complete dilatation in multiparas, or during a rapidly progressing labor. In one such study, 31% of women experienced loss of a bearing down reflex following pudendal nerve block, with 13% reporting that they were very disturbed by this loss of the urge to push.11 The authors concluded that pudendal nerve block should not be given routinely before birth but may have value when parturients are in need of pain relief in the pudendal area. This study did not evaluate the effect of the loss of the urge to bear down on the length of labor in comparison to a control group. Pudendal nerve block does not abolish the pain of uterine contractions and cervical dilation nor is it effective for repair of lacerations of the upper vagina and cervix. It is ineffective for pain relief associated with manual exploration of the uterine cavity or mid-forceps-assisted births, and may be incomplete for cervical repair and forceps rotation.13 Contraindications are patients that decline or are unable to cope with the procedure, coagulation disorders, infection in the vagina, and allergy to local anesthetic. The effectiveness of pudendal nerve block is dependent on the knowledge and skill of the providers who administer it. Studies report ineffective block on one or both sides in 3% to 50% of blocks.13-16 A 2013 prospective audit17 designed to determine current knowledge and technique of pudendal nerve block found that of 57 obstetrician participants, all were able to identify the ischial spine as the key landmark for pudendal nerve block placement. None of the study group, however, was able to describe correctly the optimal point of infiltration to most effectively target the pudendal nerve or to describe the correct amount of time required to effect adequate analgesia. Only 14% of participants knew the correct depth of infiltration. When demonstrating the point of pudendal nerve block infiltration on pelvic models, the study group’s average point of infiltration was 20 mm from the optimal point of infiltration, a distance that may likely decrease its effectiveness. The authors concluded that poor knowledge and variable performance of pudendal nerve block may be contributing to suboptimal effectiveness and opined that this may partially be a result of reduced exposure to pudendal nerve block in the context of increasing epidural and spinal anesthesia use, a lack of research, and failure of both obstetric and anesthetic textbooks to advocate for the technique. TECHNIQUE FOR PERFORMING PUDENDAL NERVE BLOCK
To target the pudendal nerve effectively and safely, an understanding of the location of the pudendal nerve and internal pudendal artery is essential. The pudendal nerve derives from 652
sacral roots S2-S4 and crosses posterior to the sacrospinous ligament close to where the ligament attaches to the ischial spine. The pudendal nerve lies medial to the internal pudendal vessels that lie on the posterior aspect of the ischial spine. The pudendal nerve then travels inferior to the ischial spine and branches into the dorsal nerve of the clitoris, perineal nerve, and inferior rectal nerve (Figure 1).18 Various techniques for pudendal nerve block have been described. Initially developed as a transperineal approach, pudendal nerve block technique was modified in the 1940s to a transvaginal approach, allowing a technically simpler and more accurate administration of anesthetic.4 With the transvaginal approach, a needle guide such as the Iowa trumpet, sheaths the needle and protects the vagina and presenting part from inadvertent puncture as the needle is directed in the vagina to the point of optimal infiltration. In US intrapartum care, pudendal nerve block is currently most often approached transvaginally.5 Table 1 reviews the details of the correct procedure for initiating a pudendal nerve block. In order to place the anesthetic near the pudendal nerve, the local anesthetic is injected bilaterally, 10mm medial and posterior to the ischial spines, at a depth of 10mm. Variations in transvaginal injection technique are reported in the literature. Instead of a single-injection approach, some practitioners use multiple injections.8,21 Table 2 describes the multiple injection procedures. There are no clinical trials comparing the safety or efficacy of the single or multiple injection procedures. Theoretically, fewer injections may reduce the risk of complications such as infection, inadvertent vascular injection of anesthetic, damage to the pudendal vessels, and hematoma; however, multiple injections may decrease the chance of inadequate block. LOCAL ANESTHETIC USED FOR PUDENDAL NERVE BLOCK
The anesthetic commonly used in pudendal nerve block is 1% lidocaine.12 Lidocaine is rapidly absorbed, crosses the placenta, and is detectable in maternal venous and fetal scalp blood within 5 minutes after injection, with peak levels attained between 10 and 20 minutes after injection.12 A maximum block may take up to 20 minutes to achieve because the pudendal nerve is a large peripheral nerve with a smaller surface area to volume ratio and a myelin sheath. Hence, the speed of onset of anesthetic effect is delayed and time to maximum block takes longer to achieve than the usual 5 minutes for subcutaneous infiltration of the perineum.17 The average duration of action of lidocaine is 30 to 60 minutes.19 Safe dosing of 1% lidocaine is 3mg/kg (204 mg in a woman who is 150 lbs)17 to 4.5mg/kg (300mg in a woman who is 150 lbs). The maximum recommended dose is 300mg.19 Other anesthetics that have been used for pudendal nerve blocks include 1% mepivacaine (Carbocaine), 0.25% bupivacaine (Marcaine), and 2% 2-chloroprocaine (Nesacaine).14 Because of its rapid onset of action, 2% solution of 2chloroprocaine can be used immediately before birth. It does, however, have the disadvantage of a shorter duration of action (15-30 minutes).5 In older studies, investigators evaluated whether the addition of low-dose epinephrine to lidocaine or mepivacaine Volume 59, No. 6, November/December 2014
Figure 1. Anatomy of the Pudendal Nerve Adapted with permission from Rohen.19
increased the intensity and duration of the analgesic effect. In a prospective double-blind randomized controlled trial (RCT) of 151 women receiving pudendal nerve block in the second stage of labor, Schierup14 found no difference in the effectiveness of the analgesic block when 20 mg of 1% mepivacaine with or without epinephrine were compared. Other trials have reported that the addition of epinephrine to lidocaine or mepivacaine is associated with a more effective block. In an RCT of 865 women receiving pudendal nerve block before or during the second stage, LanghoffRoos11 found pudendal nerve block with epinephrine added to 1% mepivacaine had a significantly better analgesic effect than 1% mepivacaine without epinephrine (P ⬍ .01) or 0.25% bupivacaine without epinephrine (P ⬍ .05). Zador12 compared the analgesic effect of pudendal nerve block administered to women who were fully dilated with lidocaine, with and without epinephrine. Pudendal block with lidocaine and epinephrine at a 1:200,000 concentration was associated with better pain relief scores and a longer duration of analgesia. Statistical significance was not reported. The lack of current research combined with the limited and conflicting available research data make it difficult to assess any additional pain relief benefit for the addition of epinephrine to pudendal nerve block. Although Journal of Midwifery & Women’s Health r www.jmwh.org
there are not sufficient data to draw conclusions about whether epinephrine prolongs the duration of action of local anesthetics used to achieve pudendal nerve block, studies of the addition of epinephrine to local anesthetics used in anesthesia for other areas of the body have demonstrated a prolongation of the duration of action of local anesthetics.22 However, any potential benefit of adding epinephrine to pudendal nerve block is likely outweighed by the risks of its adverse effects on labor. Contemporary obstetric texts do not include recommendations for the addition of epinephrine to local anesthetics used in pudendal nerve blocks.5,21
EFFECTS OF PUDENDAL NERVE BLOCK ON LABOR
The research from Schierup,14 Langhoff-Roos,11 and Zador12 also addressed the effect on labor of different anesthetic agents, with and without additional epinephrine. Zador12 studied the length of second stage in 24 randomly selected women who, at the onset of second stage, received pudendal nerve block with 200 mg of 1% lidocaine, with and without epinephrine (1:200,000), and compared them to a control group without pudendal nerve block. Pudendal nerve block 653
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retracted into the guide until you are ready to advance the needle through the ligament. Make sure that your fingers are not in front of the tip of the guide before advancing the needle. Continued.
• Caution! When the needle is fully advanced through the guide, it will protrude 10-15 mm (varies with manufacturer) from the tip of the guide. To prevent needle stick injuries keep the needle
6. Advance the needle through the guide and through the sacrospinous ligament to the optimal point of infiltration.
• A gentle forward pressure of the index finger on the ischial spine may help to stabilize it.
5. Stabilize the guide.
the parturient to breathe deep between contractions may help her to overcome the urge to bear down during the procedure.
• Placing the pudendal nerve block while the fetal head is deep in the pelvis can be challenging as the procedure often stimulates an urge to push. Placing it between contractions and encouraging
needle to protrude from its end and varies with manufacturer.
• The correct location of the guide directs the needle tip to the optimal point of infiltration (10 mm medial and 10-15 mm posterior to the ischial spine). The needle guide allows only 10-15 mm of
• For a left-sided block, place the left index finger on the ischial spine and hold the guide and attached syringe in your right hand.
left hand, glide it along your right hand to the point between the tips of your index and middle finger (Figure 3).20
• To perform a right-sided block, place your right index finger on the ischial spine. Place your middle finger on the adjacent sacrospinous ligament. Holding the guide and attached syringe in your
• To prevent inadvertent needle sticks, make sure the needle tip is withdrawn into the guide during insertion into the vagina.
4. With the needle tip withdrawn into the guide, insert the guide with attached syringe into the vagina. Place the tip of the guide on the sacrospinous ligament, 10 mm medial to the ischial spine.
sacrum), find the attached sacrospinous ligament, and walk your fingers laterally along the ligament to the ischial spine.
that travels between the sacrococcygeal joint and the ischial spine. If the location of the sacrospinous ligament is unclear, palpate the sacrococcygeal joint (the junction between the coccyx and the
• If the location of the ischial spine is unclear, palpate the sacrospinous ligament, and follow it laterally to its attachment point on the ischial spine. The sacrospinous ligament is a firm band of tissue
3. Palpate the ischial spine.
2. Draw up 20 cc of 1% lidocaine into the syringe, attach the pudendal needle and clear the air from the syringe and needle. Place the needle with attached syringe into the guide (Figure 2).
1. Explain the risks and benefits of pudendal nerve block and obtain consent.
Table 1. Procedure for Pudendal Nerve Block, Single Injection Approach
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Adapted from Chestnut DH5 and Ford JM.17
is not complete before the procedure.
with local anesthetic, then administer the pudendal nerve block. This will provide a more rapid anesthetic block to the perineum and help with pain relief if the effect of the pudendal nerve block
• In some cases, such as urgent births due to fetal distress where it may not be possible to wait up to 20 minutes to achieve maximum anesthetic effect, practitioners may first infiltrate the perineum
• If the block is ineffective or unilateral, 5 additional mL of 1% lidocaine may be administered. Keep track of the total dose administered and do not exceed 30 mL (300 mg) of 1% lidocaine.
the anal sphincter. Repeat on the opposite side.
• The maximum analgesic effect may take up to 20 minutes to achieve. To test for an effective block, stroke the skin adjacent to the anus. An effective block will prevent the reflexive constriction of
10. Allow sufficient time to achieve an effective block.
9. Repeat the procedure on the contralateral side.
• Alert the woman to the forthcoming injection.
8. Inject 10 cc of lidocaine into the first side.
• This is a necessary safety measure to prevent intravascular administration. Aspiration is performed before all subsequent injections.
7. Aspirate.
Table 1. Procedure for Pudendal Nerve Block, Single Injection Approach
Table 2. Variations of Pudendal Nerve Block Procedure, Multiple Injection Approach
Follow the procedure in Table 1 until the point of administration of 1% lidocaine. Instead of a single injection approach: Method 18 Inject 3 mL of 1% lidocaine into the sacrospinous ligament 10mm medial and posterior to ischial spine. Advance the needle through the sacrospinous ligament and inject the remaining 7 mL. Aspirate before all injections. Repeat on other side. Method 219 Inject 1mL of 1% lidocaine into the mucosa and create a mucosal wheal just beneath the tip of the ischial spine. Advance the needle to the sacrospinous ligament and infiltrate 3 mL into the sacrospinous ligament. Advance the needle through the sacrospinous ligament and inject another 3 mL of 1% lidocaine posterior to the ligament. Withdraw the needle into the guide, place it just above the ischial spine, and administer an additional 3 mL of 1% lidocaine. Aspirate before all injections. Repeat on other side. Adapted from Kurzel RB8 and Cunningham FG.19
Figure 2. Pudendal Nerve Block Set (Needle, Guide, Syringe)
initiated with 1% lidocaine without epinephrine, was associated with a longer mean duration of the second stage, in both nulliparas and multiparas (15 minutes and 5 minutes respectively) when compared to the women in the control group who did not have a pudendal nerve block. The addition of epinephrine to the pudendal nerve block was also associated with a longer mean duration of the second stage in nulliparas (20 minutes longer in nulliparas; no multiparas in this group) when compared to the women in the control group. Of the 5 women who had a vacuum-assisted birth, 4 were in the group with 1% lidocaine with epinephrine. Statistical significance was not reported. The authors attributed the increase in mean duration of second stage to the abolishment of the bearing down reflex. The RCT by Schierup14 compared the effect of pudendal nerve block administered at the end of second stage, with 20 cc of 1% mepivacaine (Carbocaine) with and without epinephrine. Women who received a pudendal nerve block with 1% mepivacaine with epinephrine had a slightly longer (P ⬍ .02) time interval from pudendal nerve block to birth
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(ranging from 1-24 minutes longer, mean of 4 minutes) compared to the women who received 1% mepivacaine without epinephrine. This time difference may or may not have clinical significance. The authors concluded that 20 cc of 1% mepivacaine without epinephrine is an effective choice for pudendal nerve block without the potential disadvantages of adding epinephrine. The RCT by Langhoff-Roos11 evaluated the effect on labor of pudendal nerve block with 3 different local anesthetics: 1% mepivacaine without epinephrine, 1% mepivacaine with epinephrine, and 0.25% bupivacaine without epinephrine. Pudendal nerve block was administered to 865 women before and during the second stage. Loss of the urge to bear down was reported by 31% of all of the women who received the pudendal nerve block. Loss of the bearing down reflex was more common among the women in the group who received pudendal nerve block with 1% mepivacaine and epinephrine, compared to the women who received 1% mepivacaine without epinephrine or 0.25% bupivacaine without epinephrine (P ⬍ .01). Among the 3 groups, mean time from pudendal nerve block to birth, mean duration of the second stage, frequency of vacuum extractions, and frequency of intravenous oxytocin administration was the same in all groups. Intranasal oxytocin was used significantly more often by the women in the 1% mepivacaine with epinephrine group (P ⬍ .05) compared with the other 2 groups. The study findings were not, however, compared to a control group without pudendal nerve block. Based on this limited and older data, pudendal nerve block is associated with a decreased urge to bear down and a possible increase in the length of the second stage and analgesic block to birth time, with unclear clinical significance. Providing anticipatory guidance to parturients about the possible loss of the urge to push, followed by supportive guidance during pushing efforts during the second stage, may be helpful to women who choose pudendal nerve block. The addition of epinephrine to lidocaine or mepivacaine with pudendal nerve block may result in more adverse effects on labor than pudendal nerve block without epinephrine.
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Figure 3. Pudendal Nerve Block Technique. The tip of the pudendal guide is placed on the sacrospinous ligament, 1cm medial to the ischial spine. The needle is advanced 1cm through the sacrospinous ligament, and following aspiration, the local anesthetic is injected. Adapted with permission from Gabbe SW.20
NEONATAL EFFECTS OF PUDENDAL NERVE BLOCK
When the neurobehavioral responses of newborns whose mothers received bupivacaine, mepivacaine, or 2-chloroprocaine for pudendal nerve block were studied, there was no significant effect of any of the agents on newborn neurobehavioral indices at 4 and 24 hours, with the exception of a better response to pinprick at 4 hours in the mepivacaine-exposed neonate.23 The author was unable to find any published trials addressing the effect of pudendal nerve block on breastfeeding behaviors. COMPLICATIONS OF PUDENDAL NERVE BLOCK
Complications of pudendal nerve block are rare but can be serious. Systemic toxicity due to inadvertent intravascular administration or excessive doses of anesthetic may result in tinnitus, disorientation, drowsiness, confusion, loss of consciousness, palpitations, hypotension, bradycardia, convulsions, and coma.5 This can be prevented with careful aspiration before injection of the anesthetic and attention to total dose of anesthetic. Emergency resuscitation equipment should be available when administering a pudendal nerve block. Inadvertent vascular injury of a pudendal vessel in the course of initiating pudendal nerve block may result in a retroperitoneal hematoma and subsequent infection of the hematoma. They are usually small and surgical intervention is rarely needed. The classic signs and symptoms of an infected retroperitoneal hematoma are a postpartum temperature elevation with a decreasing hematocrit. Other signs and symptoms include pain in the abdomen or hip on the side of pudendal nerve block, fever, chills, increasing abdominal pain with radiation to the lower quadrant, decreased bowel sounds, and deviation of the uterus away from the hematoma. Journal of Midwifery & Women’s Health r www.jmwh.org
Infected retroperitoneal hematomas may often be treated conservatively with antibiotics.8 Most women have no sequelae if blood is aspirated during the pudendal nerve block procedure. Keep in mind, however, the possibility of hematoma formation during the postpartum course. Hematoma formation may also occur without observing aspirated blood during pudendal nerve block, for example, when a pudendal needle passes through a vessel and aspiration yields no blood. Women with defective coagulation have a higher risk of hematoma.8 Contamination by vaginal or rectal flora during pudendal nerve block may result in localized infection. Retropsoas and subgluteal abscesses following pudendal nerve block have been reported. A diagnosis of retropsoas or subgluteal abscess should be considered in the woman who has received pudendal nerve block and is experiencing vague to severe pain in the hip, leg, buttock, back, abdomen, or perineum during the early postpartum period. This is often accompanied by increasing fever and limp. Management includes treatment with antibiotics, incision and drainage, and close follow-up. Commonly cultured organisms are Escherichia coli, Bacteroides, and anaerobic Streptococcus.24 Other unlikely complications include allergic reaction to the anesthetic, pudendal nerve damage, temporary paresthesia in the ischial region,11 sacral neuropathy, and inadvertent needle puncture of the mother or provider. Fetal and neonatal complications are extremely rare and include inadvertent injection of anesthetic into the scalp and needle puncture. One case report described 3 cases of neonatal lidocaine intoxication.25
CONCLUSION
Skilled administration of pudendal nerve block can provide rapid and effective pain relief for women who choose not 657
to use neuraxial analgesia or who do not have the option of epidural or spinal anesthesia and would like assistance with pain relief at the end of the second stage, with operative vaginal birth or with perineal repair. In this case, KS was administered a pudendal nerve block with 1% lidocaine, and it provided effective anesthesia for a vacuum-assisted birth and subsequent repair of a seconddegree perineal laceration. Key elements to effective pudendal nerve block include knowledge of pudendal nerve anatomy, accurate technique to ensure injection of local anesthetic at the optimum point of infiltration, and an understanding of the time required to effect adequate anesthesia. In this case, there was ample time to allow the anesthesia to take full effect before beginning the vacuum-assisted birth. If an urgent operative vaginal birth is anticipated, providers may offer and place a pudendal nerve block while waiting for the arrival of a consultant or during preparations for the operative vaginal birth. This may help to ensure that women have adequate pain relief for the birth. To guide clinical practice, further research is needed to evaluate and compare the effectiveness and safety of single and multiple injection approaches to pudendal nerve block and to explore methods for optimizing the technique and improving efficacy. Additionally, studies of the effect of pudendal nerve block on breastfeeding behaviors are needed. In a culture where epidural rates are increasing, and opportunities for pudendal nerve block may be decreasing, maintaining one’s skill and confidence in pudendal nerve block may require periodic practice on pelvic models. Training in the pudendal nerve block technique should continue to be a valued part of midwifery education curriculum and obstetric residency programs. The development of new hands-on teaching models combined with written and visual training resources are needed to assist with the training and maintenance of this skill. As midwives and physicians renew our awareness and knowledge of this effective pain relief option and pass this skill on to the next generation of practitioners, the women we care for will benefit from having the option of this simple and effective pain relief method. AUTHOR
Deborah Anderson, CNM, MSN, IBCLC, practices midwifery at San Francisco General Hospital. She is an Associate Clinical Professor at the University of California, San Francisco, Department of OB/GYN/RS, and in the San Francisco General Hospital/University of California, San Francisco Interdepartmental Nurse-Midwifery Education Program. CONFLICT OF INTEREST
The author reports no conflicts of interest. REFERENCES 1.Rosen R, Hughes S, Levinson G. Regional anesthesia for labor and delivery. In: Hughes S, Levinson G, Rosen M, eds. Shnider and levinson’s anesthesia for obstetrics. 4th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2002:123-133.
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2.Schuenke M, Schulte E, Schumacher U. The nerves of the sacral plexus: The pudendal and coccygeal nerves. In: Ross L, Lamperti E, eds. Thieme atlas of anatomy. New York: Thieme; 2006:482483. 3.Aissaoui Y, Bruyere R, Mustapha H, Bry D, Kamili ND, Miller C. A randomized controlled trial of pudendal nerve block for pain relief after episiotomy. Anesth Analg. 2008;107(2):625-629. 4.Buckley JJ, Dugger JH, Kegel EE. Transvaginal pudendal-nerve block– the safe anesthesia in obstetrics; report of seven years’ experience. Obstet Gynecol. 1956;8(4):393-395. 5.Chestnut DH. Alternative regional anesthetic techniques: Paracervical block, lumbar sympathetic block, pudendal nerve block, and perineal infiltration. In: Chestnut D, Polley L, Tsen L, Wong C, eds. Chestnut’s obstetric anesthesia: Principles and practice. 4th ed. Philadelphia: Mosby/Elsevier; 2009:493-500. 6.Novikova N, Cluver C. Local anaesthetic nerve block for pain management in labour. Cochrane Database Syst Rev. 2012;4:CD009200. 7.Goldman JA. Pudendal block anaesthesia in obstetrics. A review of 510 operative deliveries. Br J Anaesth. 1959;31:538-542. 8.Kurzel RB, Au AH, Rooholamini SA. Retroperitoneal hematoma as a complication of pudendal block. diagnosis made by computed tomography. West J Med. 1996;164(6):523-525. 9.Ahlberg M, Saltvedt S, Ekeus C. Insufficient pain relief in vacuum extraction deliveries: A population-based study. Acta Obstet Gynecol Scand. 2013;92(3):306-311. 10.Pace MC, Aurilio C, Bulletti C, Iannotti M, Passavanti MB, Palagiano A. Subarachnoid analgesia in advanced labor: A comparison of subarachnoid analgesia and pudendal block in advanced labor: Analgesic quality and obstetric outcome. Ann N Y Acad Sci. 2004;1034:356363. 11.Langhoff-Roos J, Lindmark G. Analgesia and maternal side effects of pudendal block at delivery. A comparison of three local anesthetics. Acta Obstet Gynecol Scand. 1985;64(3):269-272. 12.Zador G, Lindmark G, Nilsson BA. Pudendal block in normal vaginal deliveries. clinical efficacy, lidocaine concentrations in maternal and foetal blood, foetal and maternal acid-base values and influence on uterine activity. Acta Obstet Gynecol Scand Suppl. 1974;(34)(34):5164. 13.Hutchins CJ. Spinal analgesia for instrumental delivery. A comparison with pudendal nerve block. Anaesthesia. 1980;35(4):376377. 14.Schierup L, Schmidt JF, Torp Jensen A, Rye BA. Pudendal block in vaginal deliveries. mepivacaine with and without epinephrine. Acta Obstet Gynecol Scand. 1988;67(3):195-197. 15.Scudamore JH, Yates MJ. Pudendal block–a misnomer? Lancet. 1966;1(7427):23-24. 16.Kobak AJ, Evans EF, Johnson GR. Transvaginal pudendal nerve block; a simple procedure for effective anesthesia in operative vaginal delivery. Am J Obstet Gynecol. 1956;71(5):981-989. 17.Ford JM, Owen DJ, Coughlin LB, Byrd LM. A critique of current practice of transvaginal pudendal nerve blocks: A prospective audit of understanding and clinical practice. J Obstet Gynaecol. 2013;33(5):463465. 18.Standring S, ed. Gray’s Anatomy : The Anatomical Basis of Clinical Practice. 39th ed. Edinburgh: Elsevier Churchill Livingstone; 2005. 19.Rohen JW, Yokochi D, Lutjen-Drecoll E. Color Atlas of Anatomy: A Photographic Study of The Human Body. Lippincott Williams & Wilkins, 2002. 20.Niebyl JR, Simpson JL. Obstetrics Normal and Problem Pregnancies. Churchill Livingstone, 2007 21.Cunningham FG. Obstetrical Anesthesia. In: Cunningham FG, ed. William’s obstetrics. 23nd ed. New York: McGraw-Hill; 2010:478-479. 22.Bailard N, Ortiz J, Flores R. Additives to local anesthetic for peripheral nerve blocks: Evidence, limitations, and recommendations. Am J Health-Syst Pharm. 2014;71(Mar 2, 1014):373. 23.Merkow AJ, McGuinness GA, Erenberg A, Kennedy RL. The neonatal neurobehavioral effects of bupivacaine, mepivacaine, and 2chloroprocaine used for pudendal block. Anesthesiology. 1980;52(4): 309-312. Volume 59, No. 6, November/December 2014
24.Svancarek W, Chirino O, Schaefer G, Jr, Blythe JG. Retropsoas and subgluteal abscesses following paracervical and pudendal anesthesia. JAMA. 1977;237(9):892-894. 25.Pages H, de la Gastine B, Quedru-Aboane J, Guillemin MG, LelongBoulouard V, Guillois B. Lidocaine intoxication in newborn following maternal pudendal anesthesia: Report of three cases. J Gynecol Obstet Biol Reprod (Paris). 2008;37(4):415-418.
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Clinical Rounds
Pudendal Nerve Block for Vaginal Birth Deborah Anderson, CNM, MSN, IBCLC
CEU
Pudendal nerve block is a safe and effective pain relief method for vaginal birth. Providing analgesia to the vulva and anus, it is used for operative vaginal birth and subsequent repair, late second stage pain relief with spontaneous vaginal birth, repair of complex lacerations, or repair of lacerations in women who are unable to achieve adequate or satisfactory pain relief during perineal repair with local anesthesia. Key to its efficacy is the knowledge of pudendal nerve anatomy, the optimal point of infiltration of local anesthetic, and an understanding of the amount of time necessary to effect adequate analgesia. c 2014 by the American College of Nurse-Midwives. J Midwifery Womens Health 2014;59:651–659 Keywords: pudendal nerve block, local anesthetics, labor analgesia, labor anesthesia, labor pain management
CASE REPORT
K.S. is a 29-year old nulliparous woman at 39 weeks’ gestation who presented to a labor and delivery unit with a 3-day history of irregular, painful contractions accompanied by an inability to sleep for the previous 2 nights. Her cervical examination was unchanged (2 cm dilated, 80% effaced, -3 station, and posterior) from her previous examination 24 hours earlier. She had a normal antepartum course, her vital signs were normal, the estimated fetal weight was 3300 g, and the fetal heart rate was Category 1. K.S. was admitted for therapeutic rest, and after obtaining her consent, she was given 15 mg of intramuscular morphine sulfate and 25 mg of intramuscular hydroxyzine (Vistaril). She slept for 6 hours and awoke with regular contractions, and her cervical examination was 4 cm dilated, 90% effaced, -3 station. K.S.’s labor then progressed normally through the active phase. She chose nonpharmacologic methods of pain relief to help her work with the pain of labor. During the second stage, her fetus rotated from right occiput posterior to right occiput anterior position. Three hours after the second stage started, the fetus was at a +3 station but had made no descent over the course of the previous hour. K.S. reported exhaustion and an inability to push, and despite continuous supportive guidance, position change, rest, adequate hydration, and frequent strong contractions, she was making little pushing effort. At that point, she was unable to push further and asked for assistance with the birth. The fetal heart rate throughout labor was Category 2, at 150 bpm, moderate variability, and occasional mild to moderate variable decelerations. Given evidence of maternal exhaustion and her request for assistance, the consulting physician was contacted, and the midwife and consulting physician reviewed with K.S. the option of continued pushing efforts or vacuum-assisted birth with anesthesia. She elected to go forward with a vacuum-assisted birth and pudendal nerve block. The risks and benefits of vacuumassisted vaginal birth and pudendal nerve block were reviewed, and she consented.
A pudendal nerve block was placed bilaterally with 1% lidocaine (Xylocaine), 10mL (100mg). Twenty minutes following placement of the pudendal nerve block, adequate anesthesia was achieved, and a vacuum-assisted vaginal birth was performed. K.S. sustained a second-degree perineal laceration that was repaired with analgesia provided by the continuing pudendal nerve block. Her postpartum course was uneventful, and she was discharged home with her newborn 2 days later. INTRODUCTION
Address correspondence to Deborah Anderson, CNM, MSN, IBCLC. E-mail: [email protected]
Second-stage labor pain originates from the increasing distention of the vagina, vulva, and perineum.1 Pain impulses travel via the sensory and motor fibers of the bilateral pudendal nerves, which are the primary source of sensory innervation to the lower vagina, vulva, perineum, and anus. The pudendal nerve also provides motor innervation to the perineal muscles, urethral sphincter, and external anal sphincter.2 Infiltration of local anesthesia around the trunk of the pudendal nerve inhibits nerve transmission and provides safe and effective pain relief for vaginal birth.3,4 In obstetrics, pudendal nerve block is primarily used to achieve analgesia for operative vaginal birth and/or repair of genital tract lacerations1,5 although it may also be used for second stage pain relief for women who are close to having a spontaneous vaginal birth. Pudendal nerve block may also be initiated for women who do not have adequate or satisfactory pain relief during perineal repair following instillation of local anesthesia to the perineum. Prior to the widespread use of epidural anesthesia in obstetrics, pudendal nerve block was a commonly used anesthesia technique for vaginal birth.6 Reported as early as 19087 pudendal nerve block became popular in the mid-1950s4 and was an often used anesthesia for childbirth into the mid1980s. As epidural use grew in popularity, pudendal nerve block declined in the United States. An estimated 5% to 10% of parturients received pudendal nerve block in the mid1990s.8 Similarly, use of pudendal nerve block in Sweden declined from 50% in the 1970s to 4% in recent years.9 A 2004 study from Italy cited pudendal nerve block as the anesthetic procedure most commonly used in Europe when no
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analgesia was requested by parturients or in hospitals without a service for obstetric analgesia.10 There are no published surveys addressing current obstetric use of pudendal nerve block in the United States. Effectiveness of Pudendal Nerve Block
Because the bearing down reflex may be blocked following pudendal anesthesia, second stage pudendal nerve block is usually administered immediately before birth.5 Older studies from Sweden11,12 report use of pudendal nerve block throughout the second stage, just prior to complete dilatation in multiparas, or during a rapidly progressing labor. In one such study, 31% of women experienced loss of a bearing down reflex following pudendal nerve block, with 13% reporting that they were very disturbed by this loss of the urge to push.11 The authors concluded that pudendal nerve block should not be given routinely before birth but may have value when parturients are in need of pain relief in the pudendal area. This study did not evaluate the effect of the loss of the urge to bear down on the length of labor in comparison to a control group. Pudendal nerve block does not abolish the pain of uterine contractions and cervical dilation nor is it effective for repair of lacerations of the upper vagina and cervix. It is ineffective for pain relief associated with manual exploration of the uterine cavity or mid-forceps-assisted births, and may be incomplete for cervical repair and forceps rotation.13 Contraindications are patients that decline or are unable to cope with the procedure, coagulation disorders, infection in the vagina, and allergy to local anesthetic. The effectiveness of pudendal nerve block is dependent on the knowledge and skill of the providers who administer it. Studies report ineffective block on one or both sides in 3% to 50% of blocks.13-16 A 2013 prospective audit17 designed to determine current knowledge and technique of pudendal nerve block found that of 57 obstetrician participants, all were able to identify the ischial spine as the key landmark for pudendal nerve block placement. None of the study group, however, was able to describe correctly the optimal point of infiltration to most effectively target the pudendal nerve or to describe the correct amount of time required to effect adequate analgesia. Only 14% of participants knew the correct depth of infiltration. When demonstrating the point of pudendal nerve block infiltration on pelvic models, the study group’s average point of infiltration was 20 mm from the optimal point of infiltration, a distance that may likely decrease its effectiveness. The authors concluded that poor knowledge and variable performance of pudendal nerve block may be contributing to suboptimal effectiveness and opined that this may partially be a result of reduced exposure to pudendal nerve block in the context of increasing epidural and spinal anesthesia use, a lack of research, and failure of both obstetric and anesthetic textbooks to advocate for the technique. TECHNIQUE FOR PERFORMING PUDENDAL NERVE BLOCK
To target the pudendal nerve effectively and safely, an understanding of the location of the pudendal nerve and internal pudendal artery is essential. The pudendal nerve derives from 652
sacral roots S2-S4 and crosses posterior to the sacrospinous ligament close to where the ligament attaches to the ischial spine. The pudendal nerve lies medial to the internal pudendal vessels that lie on the posterior aspect of the ischial spine. The pudendal nerve then travels inferior to the ischial spine and branches into the dorsal nerve of the clitoris, perineal nerve, and inferior rectal nerve (Figure 1).18 Various techniques for pudendal nerve block have been described. Initially developed as a transperineal approach, pudendal nerve block technique was modified in the 1940s to a transvaginal approach, allowing a technically simpler and more accurate administration of anesthetic.4 With the transvaginal approach, a needle guide such as the Iowa trumpet, sheaths the needle and protects the vagina and presenting part from inadvertent puncture as the needle is directed in the vagina to the point of optimal infiltration. In US intrapartum care, pudendal nerve block is currently most often approached transvaginally.5 Table 1 reviews the details of the correct procedure for initiating a pudendal nerve block. In order to place the anesthetic near the pudendal nerve, the local anesthetic is injected bilaterally, 10mm medial and posterior to the ischial spines, at a depth of 10mm. Variations in transvaginal injection technique are reported in the literature. Instead of a single-injection approach, some practitioners use multiple injections.8,21 Table 2 describes the multiple injection procedures. There are no clinical trials comparing the safety or efficacy of the single or multiple injection procedures. Theoretically, fewer injections may reduce the risk of complications such as infection, inadvertent vascular injection of anesthetic, damage to the pudendal vessels, and hematoma; however, multiple injections may decrease the chance of inadequate block. LOCAL ANESTHETIC USED FOR PUDENDAL NERVE BLOCK
The anesthetic commonly used in pudendal nerve block is 1% lidocaine.12 Lidocaine is rapidly absorbed, crosses the placenta, and is detectable in maternal venous and fetal scalp blood within 5 minutes after injection, with peak levels attained between 10 and 20 minutes after injection.12 A maximum block may take up to 20 minutes to achieve because the pudendal nerve is a large peripheral nerve with a smaller surface area to volume ratio and a myelin sheath. Hence, the speed of onset of anesthetic effect is delayed and time to maximum block takes longer to achieve than the usual 5 minutes for subcutaneous infiltration of the perineum.17 The average duration of action of lidocaine is 30 to 60 minutes.19 Safe dosing of 1% lidocaine is 3mg/kg (204 mg in a woman who is 150 lbs)17 to 4.5mg/kg (300mg in a woman who is 150 lbs). The maximum recommended dose is 300mg.19 Other anesthetics that have been used for pudendal nerve blocks include 1% mepivacaine (Carbocaine), 0.25% bupivacaine (Marcaine), and 2% 2-chloroprocaine (Nesacaine).14 Because of its rapid onset of action, 2% solution of 2chloroprocaine can be used immediately before birth. It does, however, have the disadvantage of a shorter duration of action (15-30 minutes).5 In older studies, investigators evaluated whether the addition of low-dose epinephrine to lidocaine or mepivacaine Volume 59, No. 6, November/December 2014
Figure 1. Anatomy of the Pudendal Nerve Adapted with permission from Rohen.19
increased the intensity and duration of the analgesic effect. In a prospective double-blind randomized controlled trial (RCT) of 151 women receiving pudendal nerve block in the second stage of labor, Schierup14 found no difference in the effectiveness of the analgesic block when 20 mg of 1% mepivacaine with or without epinephrine were compared. Other trials have reported that the addition of epinephrine to lidocaine or mepivacaine is associated with a more effective block. In an RCT of 865 women receiving pudendal nerve block before or during the second stage, LanghoffRoos11 found pudendal nerve block with epinephrine added to 1% mepivacaine had a significantly better analgesic effect than 1% mepivacaine without epinephrine (P ⬍ .01) or 0.25% bupivacaine without epinephrine (P ⬍ .05). Zador12 compared the analgesic effect of pudendal nerve block administered to women who were fully dilated with lidocaine, with and without epinephrine. Pudendal block with lidocaine and epinephrine at a 1:200,000 concentration was associated with better pain relief scores and a longer duration of analgesia. Statistical significance was not reported. The lack of current research combined with the limited and conflicting available research data make it difficult to assess any additional pain relief benefit for the addition of epinephrine to pudendal nerve block. Although Journal of Midwifery & Women’s Health r www.jmwh.org
there are not sufficient data to draw conclusions about whether epinephrine prolongs the duration of action of local anesthetics used to achieve pudendal nerve block, studies of the addition of epinephrine to local anesthetics used in anesthesia for other areas of the body have demonstrated a prolongation of the duration of action of local anesthetics.22 However, any potential benefit of adding epinephrine to pudendal nerve block is likely outweighed by the risks of its adverse effects on labor. Contemporary obstetric texts do not include recommendations for the addition of epinephrine to local anesthetics used in pudendal nerve blocks.5,21
EFFECTS OF PUDENDAL NERVE BLOCK ON LABOR
The research from Schierup,14 Langhoff-Roos,11 and Zador12 also addressed the effect on labor of different anesthetic agents, with and without additional epinephrine. Zador12 studied the length of second stage in 24 randomly selected women who, at the onset of second stage, received pudendal nerve block with 200 mg of 1% lidocaine, with and without epinephrine (1:200,000), and compared them to a control group without pudendal nerve block. Pudendal nerve block 653
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retracted into the guide until you are ready to advance the needle through the ligament. Make sure that your fingers are not in front of the tip of the guide before advancing the needle. Continued.
• Caution! When the needle is fully advanced through the guide, it will protrude 10-15 mm (varies with manufacturer) from the tip of the guide. To prevent needle stick injuries keep the needle
6. Advance the needle through the guide and through the sacrospinous ligament to the optimal point of infiltration.
• A gentle forward pressure of the index finger on the ischial spine may help to stabilize it.
5. Stabilize the guide.
the parturient to breathe deep between contractions may help her to overcome the urge to bear down during the procedure.
• Placing the pudendal nerve block while the fetal head is deep in the pelvis can be challenging as the procedure often stimulates an urge to push. Placing it between contractions and encouraging
needle to protrude from its end and varies with manufacturer.
• The correct location of the guide directs the needle tip to the optimal point of infiltration (10 mm medial and 10-15 mm posterior to the ischial spine). The needle guide allows only 10-15 mm of
• For a left-sided block, place the left index finger on the ischial spine and hold the guide and attached syringe in your right hand.
left hand, glide it along your right hand to the point between the tips of your index and middle finger (Figure 3).20
• To perform a right-sided block, place your right index finger on the ischial spine. Place your middle finger on the adjacent sacrospinous ligament. Holding the guide and attached syringe in your
• To prevent inadvertent needle sticks, make sure the needle tip is withdrawn into the guide during insertion into the vagina.
4. With the needle tip withdrawn into the guide, insert the guide with attached syringe into the vagina. Place the tip of the guide on the sacrospinous ligament, 10 mm medial to the ischial spine.
sacrum), find the attached sacrospinous ligament, and walk your fingers laterally along the ligament to the ischial spine.
that travels between the sacrococcygeal joint and the ischial spine. If the location of the sacrospinous ligament is unclear, palpate the sacrococcygeal joint (the junction between the coccyx and the
• If the location of the ischial spine is unclear, palpate the sacrospinous ligament, and follow it laterally to its attachment point on the ischial spine. The sacrospinous ligament is a firm band of tissue
3. Palpate the ischial spine.
2. Draw up 20 cc of 1% lidocaine into the syringe, attach the pudendal needle and clear the air from the syringe and needle. Place the needle with attached syringe into the guide (Figure 2).
1. Explain the risks and benefits of pudendal nerve block and obtain consent.
Table 1. Procedure for Pudendal Nerve Block, Single Injection Approach
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Adapted from Chestnut DH5 and Ford JM.17
is not complete before the procedure.
with local anesthetic, then administer the pudendal nerve block. This will provide a more rapid anesthetic block to the perineum and help with pain relief if the effect of the pudendal nerve block
• In some cases, such as urgent births due to fetal distress where it may not be possible to wait up to 20 minutes to achieve maximum anesthetic effect, practitioners may first infiltrate the perineum
• If the block is ineffective or unilateral, 5 additional mL of 1% lidocaine may be administered. Keep track of the total dose administered and do not exceed 30 mL (300 mg) of 1% lidocaine.
the anal sphincter. Repeat on the opposite side.
• The maximum analgesic effect may take up to 20 minutes to achieve. To test for an effective block, stroke the skin adjacent to the anus. An effective block will prevent the reflexive constriction of
10. Allow sufficient time to achieve an effective block.
9. Repeat the procedure on the contralateral side.
• Alert the woman to the forthcoming injection.
8. Inject 10 cc of lidocaine into the first side.
• This is a necessary safety measure to prevent intravascular administration. Aspiration is performed before all subsequent injections.
7. Aspirate.
Table 1. Procedure for Pudendal Nerve Block, Single Injection Approach
Table 2. Variations of Pudendal Nerve Block Procedure, Multiple Injection Approach
Follow the procedure in Table 1 until the point of administration of 1% lidocaine. Instead of a single injection approach: Method 18 Inject 3 mL of 1% lidocaine into the sacrospinous ligament 10mm medial and posterior to ischial spine. Advance the needle through the sacrospinous ligament and inject the remaining 7 mL. Aspirate before all injections. Repeat on other side. Method 219 Inject 1mL of 1% lidocaine into the mucosa and create a mucosal wheal just beneath the tip of the ischial spine. Advance the needle to the sacrospinous ligament and infiltrate 3 mL into the sacrospinous ligament. Advance the needle through the sacrospinous ligament and inject another 3 mL of 1% lidocaine posterior to the ligament. Withdraw the needle into the guide, place it just above the ischial spine, and administer an additional 3 mL of 1% lidocaine. Aspirate before all injections. Repeat on other side. Adapted from Kurzel RB8 and Cunningham FG.19
Figure 2. Pudendal Nerve Block Set (Needle, Guide, Syringe)
initiated with 1% lidocaine without epinephrine, was associated with a longer mean duration of the second stage, in both nulliparas and multiparas (15 minutes and 5 minutes respectively) when compared to the women in the control group who did not have a pudendal nerve block. The addition of epinephrine to the pudendal nerve block was also associated with a longer mean duration of the second stage in nulliparas (20 minutes longer in nulliparas; no multiparas in this group) when compared to the women in the control group. Of the 5 women who had a vacuum-assisted birth, 4 were in the group with 1% lidocaine with epinephrine. Statistical significance was not reported. The authors attributed the increase in mean duration of second stage to the abolishment of the bearing down reflex. The RCT by Schierup14 compared the effect of pudendal nerve block administered at the end of second stage, with 20 cc of 1% mepivacaine (Carbocaine) with and without epinephrine. Women who received a pudendal nerve block with 1% mepivacaine with epinephrine had a slightly longer (P ⬍ .02) time interval from pudendal nerve block to birth
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(ranging from 1-24 minutes longer, mean of 4 minutes) compared to the women who received 1% mepivacaine without epinephrine. This time difference may or may not have clinical significance. The authors concluded that 20 cc of 1% mepivacaine without epinephrine is an effective choice for pudendal nerve block without the potential disadvantages of adding epinephrine. The RCT by Langhoff-Roos11 evaluated the effect on labor of pudendal nerve block with 3 different local anesthetics: 1% mepivacaine without epinephrine, 1% mepivacaine with epinephrine, and 0.25% bupivacaine without epinephrine. Pudendal nerve block was administered to 865 women before and during the second stage. Loss of the urge to bear down was reported by 31% of all of the women who received the pudendal nerve block. Loss of the bearing down reflex was more common among the women in the group who received pudendal nerve block with 1% mepivacaine and epinephrine, compared to the women who received 1% mepivacaine without epinephrine or 0.25% bupivacaine without epinephrine (P ⬍ .01). Among the 3 groups, mean time from pudendal nerve block to birth, mean duration of the second stage, frequency of vacuum extractions, and frequency of intravenous oxytocin administration was the same in all groups. Intranasal oxytocin was used significantly more often by the women in the 1% mepivacaine with epinephrine group (P ⬍ .05) compared with the other 2 groups. The study findings were not, however, compared to a control group without pudendal nerve block. Based on this limited and older data, pudendal nerve block is associated with a decreased urge to bear down and a possible increase in the length of the second stage and analgesic block to birth time, with unclear clinical significance. Providing anticipatory guidance to parturients about the possible loss of the urge to push, followed by supportive guidance during pushing efforts during the second stage, may be helpful to women who choose pudendal nerve block. The addition of epinephrine to lidocaine or mepivacaine with pudendal nerve block may result in more adverse effects on labor than pudendal nerve block without epinephrine.
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Figure 3. Pudendal Nerve Block Technique. The tip of the pudendal guide is placed on the sacrospinous ligament, 1cm medial to the ischial spine. The needle is advanced 1cm through the sacrospinous ligament, and following aspiration, the local anesthetic is injected. Adapted with permission from Gabbe SW.20
NEONATAL EFFECTS OF PUDENDAL NERVE BLOCK
When the neurobehavioral responses of newborns whose mothers received bupivacaine, mepivacaine, or 2-chloroprocaine for pudendal nerve block were studied, there was no significant effect of any of the agents on newborn neurobehavioral indices at 4 and 24 hours, with the exception of a better response to pinprick at 4 hours in the mepivacaine-exposed neonate.23 The author was unable to find any published trials addressing the effect of pudendal nerve block on breastfeeding behaviors. COMPLICATIONS OF PUDENDAL NERVE BLOCK
Complications of pudendal nerve block are rare but can be serious. Systemic toxicity due to inadvertent intravascular administration or excessive doses of anesthetic may result in tinnitus, disorientation, drowsiness, confusion, loss of consciousness, palpitations, hypotension, bradycardia, convulsions, and coma.5 This can be prevented with careful aspiration before injection of the anesthetic and attention to total dose of anesthetic. Emergency resuscitation equipment should be available when administering a pudendal nerve block. Inadvertent vascular injury of a pudendal vessel in the course of initiating pudendal nerve block may result in a retroperitoneal hematoma and subsequent infection of the hematoma. They are usually small and surgical intervention is rarely needed. The classic signs and symptoms of an infected retroperitoneal hematoma are a postpartum temperature elevation with a decreasing hematocrit. Other signs and symptoms include pain in the abdomen or hip on the side of pudendal nerve block, fever, chills, increasing abdominal pain with radiation to the lower quadrant, decreased bowel sounds, and deviation of the uterus away from the hematoma. Journal of Midwifery & Women’s Health r www.jmwh.org
Infected retroperitoneal hematomas may often be treated conservatively with antibiotics.8 Most women have no sequelae if blood is aspirated during the pudendal nerve block procedure. Keep in mind, however, the possibility of hematoma formation during the postpartum course. Hematoma formation may also occur without observing aspirated blood during pudendal nerve block, for example, when a pudendal needle passes through a vessel and aspiration yields no blood. Women with defective coagulation have a higher risk of hematoma.8 Contamination by vaginal or rectal flora during pudendal nerve block may result in localized infection. Retropsoas and subgluteal abscesses following pudendal nerve block have been reported. A diagnosis of retropsoas or subgluteal abscess should be considered in the woman who has received pudendal nerve block and is experiencing vague to severe pain in the hip, leg, buttock, back, abdomen, or perineum during the early postpartum period. This is often accompanied by increasing fever and limp. Management includes treatment with antibiotics, incision and drainage, and close follow-up. Commonly cultured organisms are Escherichia coli, Bacteroides, and anaerobic Streptococcus.24 Other unlikely complications include allergic reaction to the anesthetic, pudendal nerve damage, temporary paresthesia in the ischial region,11 sacral neuropathy, and inadvertent needle puncture of the mother or provider. Fetal and neonatal complications are extremely rare and include inadvertent injection of anesthetic into the scalp and needle puncture. One case report described 3 cases of neonatal lidocaine intoxication.25
CONCLUSION
Skilled administration of pudendal nerve block can provide rapid and effective pain relief for women who choose not 657
to use neuraxial analgesia or who do not have the option of epidural or spinal anesthesia and would like assistance with pain relief at the end of the second stage, with operative vaginal birth or with perineal repair. In this case, KS was administered a pudendal nerve block with 1% lidocaine, and it provided effective anesthesia for a vacuum-assisted birth and subsequent repair of a seconddegree perineal laceration. Key elements to effective pudendal nerve block include knowledge of pudendal nerve anatomy, accurate technique to ensure injection of local anesthetic at the optimum point of infiltration, and an understanding of the time required to effect adequate anesthesia. In this case, there was ample time to allow the anesthesia to take full effect before beginning the vacuum-assisted birth. If an urgent operative vaginal birth is anticipated, providers may offer and place a pudendal nerve block while waiting for the arrival of a consultant or during preparations for the operative vaginal birth. This may help to ensure that women have adequate pain relief for the birth. To guide clinical practice, further research is needed to evaluate and compare the effectiveness and safety of single and multiple injection approaches to pudendal nerve block and to explore methods for optimizing the technique and improving efficacy. Additionally, studies of the effect of pudendal nerve block on breastfeeding behaviors are needed. In a culture where epidural rates are increasing, and opportunities for pudendal nerve block may be decreasing, maintaining one’s skill and confidence in pudendal nerve block may require periodic practice on pelvic models. Training in the pudendal nerve block technique should continue to be a valued part of midwifery education curriculum and obstetric residency programs. The development of new hands-on teaching models combined with written and visual training resources are needed to assist with the training and maintenance of this skill. As midwives and physicians renew our awareness and knowledge of this effective pain relief option and pass this skill on to the next generation of practitioners, the women we care for will benefit from having the option of this simple and effective pain relief method. AUTHOR
Deborah Anderson, CNM, MSN, IBCLC, practices midwifery at San Francisco General Hospital. She is an Associate Clinical Professor at the University of California, San Francisco, Department of OB/GYN/RS, and in the San Francisco General Hospital/University of California, San Francisco Interdepartmental Nurse-Midwifery Education Program. CONFLICT OF INTEREST
The author reports no conflicts of interest. REFERENCES 1.Rosen R, Hughes S, Levinson G. Regional anesthesia for labor and delivery. In: Hughes S, Levinson G, Rosen M, eds. Shnider and levinson’s anesthesia for obstetrics. 4th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2002:123-133.
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2.Schuenke M, Schulte E, Schumacher U. The nerves of the sacral plexus: The pudendal and coccygeal nerves. In: Ross L, Lamperti E, eds. Thieme atlas of anatomy. New York: Thieme; 2006:482483. 3.Aissaoui Y, Bruyere R, Mustapha H, Bry D, Kamili ND, Miller C. A randomized controlled trial of pudendal nerve block for pain relief after episiotomy. Anesth Analg. 2008;107(2):625-629. 4.Buckley JJ, Dugger JH, Kegel EE. Transvaginal pudendal-nerve block– the safe anesthesia in obstetrics; report of seven years’ experience. Obstet Gynecol. 1956;8(4):393-395. 5.Chestnut DH. Alternative regional anesthetic techniques: Paracervical block, lumbar sympathetic block, pudendal nerve block, and perineal infiltration. In: Chestnut D, Polley L, Tsen L, Wong C, eds. Chestnut’s obstetric anesthesia: Principles and practice. 4th ed. Philadelphia: Mosby/Elsevier; 2009:493-500. 6.Novikova N, Cluver C. Local anaesthetic nerve block for pain management in labour. Cochrane Database Syst Rev. 2012;4:CD009200. 7.Goldman JA. Pudendal block anaesthesia in obstetrics. A review of 510 operative deliveries. Br J Anaesth. 1959;31:538-542. 8.Kurzel RB, Au AH, Rooholamini SA. Retroperitoneal hematoma as a complication of pudendal block. diagnosis made by computed tomography. West J Med. 1996;164(6):523-525. 9.Ahlberg M, Saltvedt S, Ekeus C. Insufficient pain relief in vacuum extraction deliveries: A population-based study. Acta Obstet Gynecol Scand. 2013;92(3):306-311. 10.Pace MC, Aurilio C, Bulletti C, Iannotti M, Passavanti MB, Palagiano A. Subarachnoid analgesia in advanced labor: A comparison of subarachnoid analgesia and pudendal block in advanced labor: Analgesic quality and obstetric outcome. Ann N Y Acad Sci. 2004;1034:356363. 11.Langhoff-Roos J, Lindmark G. Analgesia and maternal side effects of pudendal block at delivery. A comparison of three local anesthetics. Acta Obstet Gynecol Scand. 1985;64(3):269-272. 12.Zador G, Lindmark G, Nilsson BA. Pudendal block in normal vaginal deliveries. clinical efficacy, lidocaine concentrations in maternal and foetal blood, foetal and maternal acid-base values and influence on uterine activity. Acta Obstet Gynecol Scand Suppl. 1974;(34)(34):5164. 13.Hutchins CJ. Spinal analgesia for instrumental delivery. A comparison with pudendal nerve block. Anaesthesia. 1980;35(4):376377. 14.Schierup L, Schmidt JF, Torp Jensen A, Rye BA. Pudendal block in vaginal deliveries. mepivacaine with and without epinephrine. Acta Obstet Gynecol Scand. 1988;67(3):195-197. 15.Scudamore JH, Yates MJ. Pudendal block–a misnomer? Lancet. 1966;1(7427):23-24. 16.Kobak AJ, Evans EF, Johnson GR. Transvaginal pudendal nerve block; a simple procedure for effective anesthesia in operative vaginal delivery. Am J Obstet Gynecol. 1956;71(5):981-989. 17.Ford JM, Owen DJ, Coughlin LB, Byrd LM. A critique of current practice of transvaginal pudendal nerve blocks: A prospective audit of understanding and clinical practice. J Obstet Gynaecol. 2013;33(5):463465. 18.Standring S, ed. Gray’s Anatomy : The Anatomical Basis of Clinical Practice. 39th ed. Edinburgh: Elsevier Churchill Livingstone; 2005. 19.Rohen JW, Yokochi D, Lutjen-Drecoll E. Color Atlas of Anatomy: A Photographic Study of The Human Body. Lippincott Williams & Wilkins, 2002. 20.Niebyl JR, Simpson JL. Obstetrics Normal and Problem Pregnancies. Churchill Livingstone, 2007 21.Cunningham FG. Obstetrical Anesthesia. In: Cunningham FG, ed. William’s obstetrics. 23nd ed. New York: McGraw-Hill; 2010:478-479. 22.Bailard N, Ortiz J, Flores R. Additives to local anesthetic for peripheral nerve blocks: Evidence, limitations, and recommendations. Am J Health-Syst Pharm. 2014;71(Mar 2, 1014):373. 23.Merkow AJ, McGuinness GA, Erenberg A, Kennedy RL. The neonatal neurobehavioral effects of bupivacaine, mepivacaine, and 2chloroprocaine used for pudendal block. Anesthesiology. 1980;52(4): 309-312. Volume 59, No. 6, November/December 2014
24.Svancarek W, Chirino O, Schaefer G, Jr, Blythe JG. Retropsoas and subgluteal abscesses following paracervical and pudendal anesthesia. JAMA. 1977;237(9):892-894. 25.Pages H, de la Gastine B, Quedru-Aboane J, Guillemin MG, LelongBoulouard V, Guillois B. Lidocaine intoxication in newborn following maternal pudendal anesthesia: Report of three cases. J Gynecol Obstet Biol Reprod (Paris). 2008;37(4):415-418.
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