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Pudendal and paracervical block

Pudendal and paracervical block
Literature review current through: Sep 2023.
This topic last updated: Jul 06, 2023.

INTRODUCTION — Pudendal and paracervical blocks are nerve blocks used during obstetric and gynecologic procedures. These blocks are typically administered by an obstetrician or gynecologist, rather than an anesthesiologist, and are easy to learn and simple to perform.

This topic will review the indications, technique, efficacy, and risks of pudendal and paracervical blocks in obstetrics and gynecology. Related topics on nerve blocks are presented elsewhere.

(See "Overview of peripheral nerve blocks".)

(See "Overview of anesthesia".)

In this topic, when discussing study results, we will use the gender terms as they are used in the studies presented. We encourage readers to consider the specific counseling and treatment needs of transmasculine and gender-expansive individuals.

DEFINITIONS AND USES — Pudendal and paracervical blocks are nerve blocks that involve a one-time injection of local anesthetic adjacent to the nerve or plexus for pain relief. The duration and density of the block depends on the dose, concentration, and pharmacology of the chosen local anesthetic. (See "Overview of peripheral nerve blocks", section on 'Single injection'.)

Pudendal block – Pudendal block is typically used to alleviate pain from minor surgical procedures involving the perineum and from events related to delivery, such as introital distension during the second stage of labor, operative vaginal delivery, or perineal repair [1]. Of note, pudendal nerve block does not decrease the pain associated with uterine contractions and cervical dilatation in the first stage of labor. Before the widespread adoption of epidural analgesia in obstetrics, pudendal block was the preferred analgesic technique for the second stage of delivery [2]. It is still sometimes used when there are contraindications to neuraxial anesthesia and an anesthetic is needed for a low vaginal and/or posterior perineal procedure. Additionally, at least one study has reported successful use of pudendal nerve block for the placement of McDonald cerclage [3]. For patients with suspected pudendal neuralgia, pudendal block has been proposed for both diagnosis and treatment [4,5].

(See "Pharmacologic management of pain during labor and delivery", section on 'Pudendal nerve block'.)

(See "Assisted vaginal birth", section on 'Anesthesia'.)

(See "Nerve injury associated with pelvic surgery", section on 'Pudendal nerve'.)

Paracervical block – Paracervical block is most commonly used to provide analgesia during gynecologic procedures involving cervical dilation or manipulation. Typical applications include pregnancy termination, hysteroscopy, and cervical ablation or excision. In a trial of 64 nulliparous patients, paracervical block decreased pain with intrauterine device placement, although paracervical block administration itself can be painful [6]. Analgesia by paracervical block is generally unsatisfactory for control of pain during intrauterine operative procedures in conscious patients [7]. Paracervical block provides some relief from the pain of uterine contractions and cervical dilation during the active phase of labor and was a relatively common labor anesthetic prior to 1970 [8]. It is no longer used in the United States, in part because of concerns about post-block fetal bradycardia [9-11]. In addition, epidural analgesia and intermittent injections of short-acting opioids (administered by subcutaneous, intramuscular, or intravenous routes) are now widely available.

(See "First-trimester pregnancy termination: Uterine aspiration", section on 'Paracervical block'.)

(See "Second-trimester pregnancy termination: Dilation and evacuation", section on 'Anesthesia'.)

(See "Overview of hysteroscopy", section on 'Pain management'.)

(See "Cervical intraepithelial neoplasia: Ablative therapies", section on 'General procedural issues'.)

(See "Pharmacologic management of pain during labor and delivery", section on 'Pudendal nerve block'.)

PUDENDAL BLOCK

Anatomy of pudendal nerve — The basis of the pudendal block is that the lower vagina, perineum, and vulva obtain most of their sensory and motor innervation from sacral nerve roots 2, 3, and 4 via the pudendal nerve. The nerve crosses posterior to the sacrospinous ligament in close approximation to where the ligament attaches to the ischial spine [12]. Infiltration of a local anesthetic around the trunk of the pudendal nerve at the level of the ischial spine results in analgesia of these areas (lower vagina, posterior perineum and vulva).

Of note, pudendal nerve block does not abolish sensation to the anterior part of the perineum because this region is supplied by branches of the ilioinguinal and genitofemoral nerves. In addition, pudendal block does not impact the cervix or upper vagina and is ineffective for pain relief associated with uterine manipulation (eg, manual extraction of placenta) [12].

Materials — The following items are obtained:

Sterile gloves.

Prepackaged kits for pudendal block including a disposable plastic needle guide and a 20-gauge extended-length (15 cm) spinal needle. Alternatively, a nondisposable metal Iowa trumpet may be used as a needle guide.

10 mL syringe with an 18- to 20-gauge needle for drawing up anesthetic

Local anesthetic. The author uses 1 percent lidocaine without epinephrine (table 1). The toxic dose of lidocaine (3 mg/kg without epinephrine and 7 mg/kg with epinephrine) is determined prior to injection. While in two studies the addition of dilute epinephrine (5 mcg/mL) increased the block's intensity and duration, the authors also reported an increased need for oxytocin augmentation or vacuum extraction when epinephrine was used in pudendal block at delivery [13,14]. Loss of bearing-down reflex is a possible explanation for the inhibition of the second stage of labor [13]. In a different randomly assigned trial evaluating the utility of adding epinephrine to local anesthesia, there were no differences in efficacy of pudendal block when mepivacaine was used with or without epinephrine [15]. (See "Overview of peripheral nerve blocks", section on 'Local anesthetics'.)

Procedure — While either a transvaginal or transperineal approach to the ischial spine can be used, the transvaginal approach is almost always employed, except for laboring patients in whom the fetal head has descended so far that the clinician cannot access the ischial spines (figure 1). Prior to performing the procedure, the risks and benefits are reviewed with the patient and informed consent is obtained. To prepare for the nerve block, the patient is placed in the lithotomy position and the perineum and vagina are swabbed with povidone iodine or a low alcohol (4 percent) chlorhexidine solution (based on patient allergies and clinician preference). The anesthetic is drawn into the syringe with the 18- or 20- gauge needle and then the initial needle is replaced with the spinal needle.

Typically, the block is bilateral. For limited procedures strictly confined to a single side of the vagina or perineum, the block may be unilateral and is performed on the same side as the planned procedure.

Transvaginal — The transvaginal approach is described below:

First, the ischial spines are located by palpating the posterolateral vaginal sidewall and identifying the bony protrusions that are distinct from the rest of the pelvic sidewall (figure 2 and figure 3). If the examiner cannot identify the ischial spines, an alternate approach is to palpate the firm band of the sacrospinous ligament and follow it laterally from the sacrum to the ischial spine.

Next, the clinician introduces the needle guide. To perform a block on the patient's right side, the operator's right index and middle fingers are used to palpate the right ischial spine and direct the needle guide into place. The maneuver is reversed for the contralateral side.

Once the needle guide is in place, the guide is positioned to lie against the vaginal mucosa on the sacrospinous ligament, approximately 1 cm medial and inferior to the ischial spine (figure 1). When the needle guide is properly positioned, the needle is introduced into the guide and is advanced to and then through the vaginal mucosa into the sacrospinous ligament, a distance of approximately 1 cm. After aspirating to confirm the absence of an intravascular location, 3 mL of local anesthetic are injected into the ligament.

Lastly, the needle is advanced slightly until the sensation of resistance caused by the ligament is lost. The needle should now be lodged in the loose areolar tissue behind the ligament where the pudendal nerve is located. Aspiration is again performed to confirm the absence of an intravascular position (the pudendal and inferior gluteal vessels lie adjacent to the pudendal nerve), and then the remaining 7 mL of anesthetic are injected.

To achieve a bilateral block, the procedure is repeated on the contralateral side.

Transperineal — The patient is placed in lithotomy position. After appropriate skin preparation, the ischial spine is identified by inserting the left index finger through the vagina or rectum and directly palpating the spine. A 20 cm 20-gauge needle will be guided to this point transcutaneously. The vaginal route for the guiding finger may be blocked by descent of the presenting part, which is really the primary indication for the transperineal approach. The skin entry point lies 2.5 cm posteromedial to the ischial tuberosity (identified by palpation), overlying the ischiorectal fossa. The needle is introduced at right angle to the skin and is advanced lateral to the guiding finger, at all times within the ischiorectal fossa. The syringe is not attached until the needle has reached its final position, approximately 1 cm caudal to the ischial spine along the sacrospinous ligament. The remainder of the steps are as described for the vaginal approach. The same procedure is carried out on the other side. Whether the same guiding finger is used or not will depend on the preference of the operator.

The transperineal approach is less efficacious than the transvaginal approach and therefore much less used. It has been reported that the bilateral success rate for pudendal blockade is approximately 50 percent with the use of the transvaginal route and only 25 percent with the transperineal route [16].

Outcome and efficacy — Within four to five minutes of the injection, a successful block will allow the clinician to pinch the lower vagina and posterior vulva, first with the thumb and index finger, and then with an Allis clamp, without provoking pain. Maximum anesthesia is achieved after 10 to 20 minutes [14]; the most common cause of block failure is not allowing enough time for the anesthetic to take effect. If the block is effective on only one side, an additional 5 mL of anesthetic may be injected into the under-anesthetized side. The average duration of lidocaine-induced pudendal block is 30 to 60 minutes [12].

While pudendal block provides satisfactory analgesia in many cases, studies have reported that 10 to 50 percent of bilateral pudendal blocks are ineffective on one or both sides [15,16]. This wide variation may reflect lack of provider education and training, as reported in at least one study, rather than failure of the procedure itself [17]. As noted above, the pudendal block does not provide pain relief for the anterior perineum, upper vagina, and cervix. Subcutaneous infiltration with additional medication is typically needed to repair lacerations in these areas and is not evidence of block failure. In a trial comparing single-shot spinal anesthesia with pudendal block in laboring patients at ≥7 cm of dilation, general pain relief was better with the single-shot spinal anesthetic (bupivacaine and fentanyl), although the two techniques appeared equivalent for episiotomy repair [18].

Pudendal block does not interfere with uterine contractions and has no adverse effects on labor progress or maternal or fetal well-being, although it may make the second stage of delivery more challenging with loss of the bearing-down reflex [12,19]. Although local anesthetics cross the placenta, pudendal block is not associated with immediate neonatal neurobehavioral effects, regardless of the agent used, even when given up to 16 minutes before delivery [19].

Complications — Potential complications are rare and include, in descending order of frequency:

Hematoma – Hematoma formation from perforation of a blood vessel during needle insertion. Patients with bleeding diatheses or on anticoagulants are at increased risk. The anesthetic does not impact the coagulation ability of pregnant patients [20]. (See "Overview of peripheral nerve blocks", section on 'Patients on antithrombotic medication'.)

Infection – Infection can occur at the site of injection. Less commonly, a localized infection can spread into the retro-psoas space, gluteal muscle, or hip joint [21].

Nerve injury – Ischial region paresthesias [13] or sacral neuropathy can result from nerve injury incurred during block placement.

Systemic toxicity – Local anesthetic systemic toxicity (LAST) can occur with intravascular administration of a local anesthetic. The signs and symptoms are presented in the table (table 2) and the topic is discussed in detail separately. (See "Local anesthetic systemic toxicity".)

Neonatal anesthetic toxicity – Neonatal local anesthetic toxicity after maternal pudendal block is extremely rare. One report described three cases of neonatal lidocaine intoxication, which manifested as transient hypotonia, apnea, seizures, mydriasis, cyanosis, and need for mechanical ventilation; all of the neonates recovered completely [22]. An older case report documented lidocaine toxicity with symptoms of post-natal apnea and bradycardia and a prolonged Q-T interval in a term infant after the mother received a pudendal block [23].

PARACERVICAL BLOCK

Anatomy of pelvic plexus — Paracervical anesthetics block transmission of pain through sympathetic, parasympathetic, and visceral sensory fibers before they enter the uterus at the level of the internal os [24]. The anatomic basis for the paracervical block is that the upper vagina, cervix, and lower uterus are innervated by the uterovaginal (or Frankenhäuser) plexus, which contains fibers derived from the inferior hypogastric (pelvic) plexus (T10-L1) and sacral nerve roots (S1-S4) (figure 4). Paracervical block does not affect the motor pathways or provide pain relief to the perineum. Therefore, when used in laboring patients, progression of labor should not be significantly affected [25], motor function of the legs is maintained and patients can ambulate, and perineal sensation persists.

Materials and choice of anesthetic — The following items should be available:

Sterile gloves.

Prepackaged kits for paracervical block including a 22-gauge extended-length (15 cm) spinal needle and a disposable plastic needle guide and spacer, which is adjusted to control the depth of needle penetration beyond the tip of the needle guide. Alternatively, a nondisposable metal Iowa trumpet may be used as a needle guide.

10 mL syringe with an 18- to 20-gauge needle for drawing up anesthetic.

Local anesthetic – The choice of anesthetic differs between gynecologic and obstetric procedures, with the main differences being that, for pregnant patients, buffered agents are preferred and vasoconstrictors are not used. A detailed discussion of local anesthetic drugs and adjuvants used in peripheral nerve blocks is reviewed in detail elsewhere. (See "Overview of peripheral nerve blocks", section on 'Drugs'.)

For gynecologic procedures – Commonly used short-acting local anesthetics include lidocaine, mepivacaine, and ropivacaine (table 1). The choice is mainly based upon availability and cost. The author uses 1 percent lidocaine with vasopressin. Lidocaine has demonstrated efficacy for first-trimester uterine evacuation procedures [26,27]. Ropivacaine is a newer amide-type anesthetic with fewer side effects [28]. A randomly-assigned double-blind trial compared 20 mL of 1 percent lidocaine plus 5 mcg/mL epinephrine with 20 mL of 0.75 percent ropivacaine without epinephrine for paracervical block during procedural abortion [29]. Use of ropivacaine resulted in less intraoperative pain than lidocaine, but there were no significant differences in the mean pain level at the end of the intervention or at two to four hours afterwards. (See "Overview of peripheral nerve blocks", section on 'Local anesthetics'.)

Many clinicians add synthetic vasopressin (commercial name Pitressin, 3 to 5 units in 10 to 20 mL of anesthetic) or epinephrine (1:200,000 or 5 mcg/mL) to the injectable anesthetic to cause local vasoconstriction and reduce intra- and postoperative blood loss [30]. Other benefits include inhibition of drug redistribution/elimination from the injection site, an increase in the potency of the block, longer duration of anesthesia, and reduced systemic toxicity. These effects are greatest when vasoconstrictors are added to short-acting anesthetics such as lidocaine and mepivacaine. Risks include the cardio-stimulatory effects of epinephrine, which may limit its utility in patients who are hypertensive, prone to cardiac tachyarrhythmias, or in whom tachycardia is not well-tolerated. Epinephrine may also increase anxiety. In addition, ischemic side effects have been reported following the administration of vasopressin and this agent is contraindicated in patients with coronary disease. (See "Overview of peripheral nerve blocks", section on 'Adjuvants'.)

For obstetric procedures – Local anesthetic that lacks epinephrine and is buffered is preferred for obstetric procedures. Chloroprocaine hydrochloride 1 percent or lidocaine 1 percent are common choices. Ester-type anesthetics (2-chloroprocaine) are metabolized by serum cholinesterase and have shorter half-lives than the amide-type anesthetics (lidocaine), which are metabolized by the liver. Some clinicians prefer an ester-type anesthetic for paracervical block because only small amounts of non-metabolized drug reach the fetus due to rapid hydroxylation in maternal plasma [31]. The theoretical disadvantage of this approach would be the relatively short duration of maternal analgesia. However, a double-blind, randomly-assigned trial in which 60 patients received either lidocaine or 2-chloroprocaine for paracervical block reported both agents produced comparable levels of analgesia that lasted approximately 40 minutes [32]. Although bupivacaine, the longest acting local anesthetic, has been widely used for paracervical block [10], its use for obstetric and gynecologic analgesia is no longer supported because it has been linked to fetal death and cardiac toxicity in healthy adults [33].

Gynecologic procedures

Procedure — Prior to performing the procedure, the risks and benefits are reviewed and informed consent is obtained. The anesthetic solution is drawn into the syringe with the short needle, which is then replaced with the spinal needle. The patient is placed in the lithotomy position. The author prepares the cervix and vaginal vault with povidone iodine or a low alcohol chlorhexidine solution; selection is based on patient allergy profile and clinician preference. A vaginal speculum and tenaculum are used for optimal exposure, and an additional needle guide is not needed.

The two common techniques for paracervical block are to inject local anesthetic into the cervicovaginal junction in either a four-point (at 2, 4, 8, and 10 o'clock) or two-point (at 4 and 8 o'clock only) fashion (figure 5). In a noninferiority trial comparing pain scores after the four- and two-point techniques in patients undergoing first trimester procedural abortion, the pain scores were similar for the two approaches, but noninferiority could not be confirmed [34]. The author prefers the two-point technique because it minimizes the number of painful injections and appears to have similar efficacy compared with the four-point technique. Regardless of number of injection sites, a total dose of 10 to 20 mL of anesthetic agent (usually 1 percent lidocaine or 2 percent chloroprocaine) is injected approximately 10 mm into the cervical stroma at the cervicovaginal junction [7,35]. Within 10 to 15 minutes, a dose of 10 mL of 1 percent lidocaine (100 mg lidocaine) achieves a peak plasma level well below the toxic range for most adult patients [36]. Of note, the maximum dose for lidocaine is 3.0 mg/kg body weight.

Outcome and efficacy — The paracervical block appears to work within minutes of injection, but the optimal amount of time to wait between injection and procedure is not known. In the above noninferiority trial, a second arm compared a three-minute wait time with no wait-time in patients who received a four-point paracervical block prior to first trimester procedural abortion and reported a nonsignificant difference between pain scores, although noninferiority could not be confirmed [34].

Efficacy of paracervical block has been debated in part because of the numerous medication and procedure combinations as well the limited ability to measure pain as an endpoint (eg, visual analog scales or use of ancillary medication). In small trials comparing paracervical block with other agents or placebo for first-trimester suction termination of pregnancy, paracervical block appears superior to placebo [26,27,37]. However, a systematic review of 26 randomly assigned or controlled trials assessing the efficacy of paracervical local anesthesia for a variety of procedures (involving both cervical dilation and uterine intervention) compared with placebo or other interventions reported mixed findings [38]. When compared with placebo:

Paracervical block reduced pain scores during cervical dilation (standard mean difference 0.37, 95% CI -0.58 to -0.17; four trials). It is not known if this difference is clinically significant.

Paracervical block reduced the risk of severe pain during uterine intervention (RR of severe pain 0.16, 95% CI 0.04-0.74; two trials) but most patients had some pain (RR of any pain 0.85, 95% CI 0.54-1.34) and some patients had severe pain.

There was no evidence that paracervical block reduced the need for additional drugs.

The authors concluded they were unable to assess whether paracervical block was inferior, equivalent, or superior to alternative analgesic techniques in terms of efficacy or safety.

Complications — Complications from paracervical block are infrequent, but when they occur they typically include bleeding from the puncture site, hematoma formation, or infection. Severe complications from paracervical block are rare and are mainly related to high doses of local anesthetic or intravascular injection (ie, local anesthetic systemic toxicity, or LAST). Symptoms can range from drowsiness and ringing in the ears to confusion, seizure, coma, and ventricular arrhythmia [39]. Symptoms, risk factors, and management are presented in the table (table 2).

Vasovagal syncope (or "cervical shock") may occur in patients who have pain during the gynecologic procedure, despite administration of a paracervical block. These episodes can be differentiated from seizure activity related to inadvertent intravascular injection because they are accompanied by bradycardia, are short and self-limited, and lack a postictal state. Treatment includes Trendelenburg position and intravenous fluid. Atropine (0.5 mg) can be used to treat such patients, but is rarely necessary [40].

Active phase of labor — If alternative pain management options are not available, a paracervical block can be used to reduce the pain associated with cervical dilation during the active phase of labor. The procedure is not effective for pain relief during the second stage because sensory nerves from the perineum are not blocked. (See "Pharmacologic management of pain during labor and delivery", section on 'Pain pathways'.)

Procedure — In order to avoid overdosing and possible cumulative effect of repeat administrations, especially with amide-type anesthetics [41], paracervical block is administered only during active labor, when cervical dilatation is between 4 cm and 8 cm, and at intervals of not less than one hour. After 8 cm dilatation, the procedure is more difficult to perform, is less effective, and has a higher risk of inducing fetal bradycardia, and is therefore not advised. Prior to performing the procedure, the risks and benefits are reviewed and informed consent is obtained. The parturient is placed in the lithotomy position. The author performs a povidone iodine or a low alcohol chlorhexidine solution prep; selection is based upon patient allergy profile and clinician preference.

To perform the procedure, the clinician's right hand is used to position the needle guide when injecting the maternal right side. Two fingers interposed between the cervix (or fetal head) and the needle guide are used to direct the tip of the guide into the lateral vaginal fornix (figure 6). The direction of the needle should be slightly lateral to the cervix and fetal head to avoid puncturing the fetus, especially when a needle spacer is not available. When the needle guide is properly positioned, the needle is inserted through the guide, taking care not to extend more than 5 mm beyond the tip of the guide. Several experts recommend an injection depth of no more than 3 mm to decrease the risk of complications, such as fetal bradycardia [10,42,43]. The syringe containing 10 mL of anesthetic is attached to the needle and, if no blood is aspirated, 5 mL of anesthetic is injected slowly into the vaginal submucosa, between contractions. After the injection has been completed, the mother is turned onto her side to maximize uteroplacental blood flow and the fetus is monitored for three minutes to assess for fetal bradycardia. Assuming the mother and fetus are stable, the same procedure is then performed on the left side, but the clinician's left hand is used for positioning the needle guide.

We believe it is safer to inject the anesthetic at 4 and 8 o'clock, rather than at 3 and 9 o'clock, because the latter sites are more vascular. A four-site injection technique (3, 5, 7, and 9 o'clock) has also been proposed to allow for anatomic variation in the distribution of nerve bundles; however, this is unlikely to be clinically important since the anesthetic spreads rapidly into the entire area at the base of the broad ligament. Anesthetic injection directly into the cervix is not advisable, given it is only partially effective (it may block pain associated with dilatation, but not the painful stimuli from the contracting uterus).

Outcome and efficacy — The onset of analgesia is rapid (two to five minutes). The duration depends upon the specific local anesthetic used; the block can be repeated during labor, but at an interval of not less than one hour. Incomplete relief of pain after paracervical block is not surprising since Frankenhäuser's plexus does not contain all of the sensory innervation of the uterus. (See 'Anatomy of pelvic plexus' above.)

In a meta-analysis of trials assessing local anesthetic nerve blocks for pain relief in labor, paracervical block was more effective than placebo (risk ratio 32.31, 95% CI 10.60-98.54, one trial, 198 participants) and opioid treatment (risk ratio 2.52, 95% CI 1.65-3.83, one trial, 109 participants) in relieving labor pain [44]. However, paracervical block was also associated with more side effects compared with placebo, including transient fetal bradycardia (risk ratio 29.0, 95% CI 1.75 to 479.61, one trial, 200 participants). While paracervical block for labor pain appeared to be efficacious, the authors agreed that the trials included were of unclear quality.

Complications

Post-block fetal bradycardia – Post-block fetal bradycardia typically occurs 2 to 10 minutes after infiltration. It is usually transient, but can last as long as 40 minutes. In studies published after 1975, all affected fetuses recovered and were delivered vaginally without signs of asphyxia; however, there are older reports of fetal acidemia, low Apgar scores, and fetal death [45]. In 2005, a prospective study from Finland involving 440 patients reported a 3.2 percent incidence of transient fetal bradycardia lasting two to eight minutes [10]. Similar rates of fetal bradycardia have been reported when epidural analgesia was administered during labor [46]; however, neonatal outcome is for the most part reassuring following epidural analgesia. The mechanism of post-block fetal bradycardia is unclear; several theories have been proposed [32,47-51].

Maternal systemic toxicity after intravascular administration – Intravascular injection of the local anesthetic may cause excessive sedation, generalized convulsions, and cardiovascular collapse (table 2). Stabilization of the mother is the first priority in these cases, and will aid intrauterine resuscitation. Treatment of systemic toxicity is discussed in detail separately. (See "Overview of peripheral nerve blocks", section on 'Local anesthetic systemic toxicity'.)

Other – Lower extremity paresthesias have been reported in up to 7 percent of cases [52], and vaginal/broad ligament hematoma or infection in 0.4 percent of cases [25]. Allergic reactions are rare with local anesthetics, but occur more often with the ester-type drugs. (See "Allergic reactions to local anesthetics".)

SUMMARY AND RECOMMENDATIONS

Definition – Pudendal and paracervical blocks are nerve blocks that involve a one-time injection of local anesthetic adjacent to the nerve or plexus for pain relief. (See 'Definitions and uses' above.)

Pudendal block – Pudendal block is typically used to alleviate pain from minor surgical procedures involving the perineum and from events related to delivery. (See 'Definitions and uses' above.)

Materials – For pudendal block, the author uses 1 percent lidocaine without epinephrine (table 1). The toxic dose of lidocaine (3 mg/kg without epinephrine and 7 mg/kg with epinephrine) is determined prior to injection. (See 'Materials' above.)

Approach and procedure – For pudendal block, either a transvaginal or transperineal approach to the ischial spine can be used (figure 2 and figure 3 and figure 1). The transvaginal approach is almost always employed, except for laboring patients in whom the fetal head has descended so far that the clinician cannot access the ischial spines. (See 'Procedure' above.)

Outcome – Within four to five minutes of the injection, a successful block will allow the clinician to pinch the lower vagina and posterior vulva, first with the thumb and index finger, and then with an Allis clamp, without provoking pain. Maximum anesthesia is achieved after 10 to 20 minutes. (See 'Outcome and efficacy' above.)

Complications – Complications, although uncommon, include hematoma formation, infection, nerve injury, and maternal and fetal drug toxicity. (See 'Complications' above.)

Paracervical block – Paracervical block is mainly used to reduce pain associated with gynecologic procedures involving cervical dilation or manipulation. Although paracervical block provides some relief from labor pain, it is no longer commonly used for labor analgesia as more effective and safer options are often available. (See 'Definitions and uses' above.)

Materials –The anesthetic selection for a paracervical block differs between gynecologic and obstetric procedures, with the main differences being that, for pregnant patients, buffered agents are preferred and vasoconstrictors are not used. (See 'Materials and choice of anesthetic' above.)

Gynecologic procedures – For patients undergoing a gynecologic procedure, the two common techniques for paracervical block are to inject local anesthetic into the cervicovaginal junction in either a four-point (at 2, 4, 8, and 10 o'clock) or two-point (at 4 and 8 o'clock only) fashion (figure 5). The author prefers the two-point technique because it minimizes the number of painful injections and appears to have similar efficacy compared with the four-point technique.

Regardless of the number of injection sites, a total dose of 10 to 20 mL of anesthetic agent (usually 1 percent lidocaine or 2 percent-chloroprocaine) is injected approximately 10 mm into the cervical stroma at the cervicovaginal junction. (See 'Gynecologic procedures' above.)

Obstetric analgesia – Paracervical block can be used in select laboring patients who do not have access to regional or systemic analgesia.

-Use in active labor – Paracervical block is administered only during active labor, when cervical dilatation is between 4 cm and 8 cm, and at intervals of not less than one hour (figure 6). After 8 cm dilatation, the procedure is more difficult to perform, is less effective, and has a higher risk of inducing fetal bradycardia, and is therefore not advised.

-Fetal monitoring for bradycardia – After the injection has been completed, the mother is turned onto her side to maximize uteroplacental blood flow and the fetus is monitored for three minutes to assess for fetal bradycardia. Post-block fetal bradycardia occurs following approximately 3 percent of injections. (See 'Active phase of labor' above.)

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Topic 5404 Version 27.0

References

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