KEY QUESTIONS
When should one consider a pudendal block as opposed to, or as an adjunct to, alternative pain or anesthetic options?
What considerations should be made surrounding complications that may arise after pudendal block placement?
What are the anatomical structures that the pudendal block innervates?
What are the key steps to the procedure?
CASE 69-1
A 30-y.o. G2P1 presents at 39 3/7 weeks gestation in active labor. Initial cervical exam shows her to be 8 cm dilated. She rapidly progresses to complete. She reflexively starts pushing in an uncoordinated manner due to severe pain. She strongly desires pain control and relief as she cries in pain. FHR tracing at this time is notable for deeply variable decelerations. The recommendation is made for an urgent assisted vaginal delivery.
Pudendal nerve blocks are an efficient and easy mode of peripheral analgesia that can be used for a variety of obstetric and gynecologic procedures. It was first introduced in 1908 by Mueller, who injected a local anesthetic directly into the perineum, vulvar, and perianal fossa.1 King described the technique in more detail in 1916 in a trial of 100 patients undergoing spontaneous delivery and perineal repair.1,2 However, the technique did not become popular or widely used until 1953, after development of the modified technique by Klink and Kohl, with the focus shifting to targeting specific nerve branches.3
The classical method of pudendal block involved a transperineal approach with local infiltration. This was best described by Gate and Dutton (1955). The technique that we use today, with a transvaginal approach, was first described in 1956 by Kobak, Evans, and Johnson.1 This technique dispensed with the original local infiltration of anesthetic, evolving to a true peripheral nerve block and targeting of the pudendal nerve.
Pudendal nerve blocks are still used for certain obstetric and gynecologic indications, but they have been displaced by an increase in the use of neuraxial anesthesia (such as epidurals or spinals), especially in the context of treatment for pain in the second stage of labor. However, many would argue that it is important for practitioners to remain competent in this method of anesthesia, especially for urgent or emergent deliveries when quick pain control and analgesia are indicated.
A pudendal nerve block provides anesthesia to the lower vagina, vulva, and surrounding tissues, with some relaxation of the pelvic floor (Fig. 69-1).
The goal of this particular nerve block is to target the pudendal nerve distal to its formation by the anterior divisions of the S2–S4 but proximal to its division into its terminal branches (Fig. 69-2).
The sacral nerve roots (S2, S3, and S4) make up the anterior sacral trucks. These come together into a single trunk 0.5 to 1 cm proximal to the ischial spine. The nerve travels through the greater sciatic foramen inferior to the pyriformis muscle (posterior to the ischial spine). As the nerve passes the inferior tip of the ischial spine, it enters the pudendal canal. The nerve further divides into three branches: the inferior hemorrhoidal nerve, the nerve of the clitoris, and the perineal nerve.
The key to localizing the pudendal nerve is to be able to appreciate the ischial spines while palpating vaginally. The pudendal vessels course just lateral to the nerve, which is another consideration during block administration (Fig. 69-3).
As mentioned previously, there are two approaches to the pudendal nerve block; the transvaginal approach and the transperineal approach. The transvaginal approach is the more popular approach in the United States and is described in detail later in this chapter.
Most providers choose 1% lidocaine as their anesthetic of choice. However, alternatives include 2-chloroprocaine 2%, bupivacaine 0.25%, prilocaine 1%, or mepivacaine 1% (Table 69-1). In a double-blind study of 1048 women, patients were randomized to receive three different types of anesthetics in their pudendal block: mepivacaine 1% plain, mepivacaine 1% with epinephrine (mepiv-epi), or bupivacaine 0.25% plain.4 The effect of mepiv-epi was significantly better than bupivacaine and mepivacaine, both before and after delivery. The women given mepivacaine with epinephrine were also found to require less supplemental anesthesia than those given mepivicaine and bupivacaine alone. However, loss of the bearing-down reflex was found in 31% of mothers, most commonly when mepivacaine with epi was used.4 Although some clinicians report that epinephrine improves the quality of the block, one study comparing mepivicaine pudendal blocks with and without epinephrine in 151 women in the second stage of labor did not show any additional benefit to adding epinephrine to mepivicaine.5
| Anesthetic Agent* | Usual Concentration (%) | Usual Volume (mL) | Onset | Average Duration (min) | Maximum Dose (mg) | Clinical Use | ||||||
| Aminoesters | ||||||||||||
| 2-Chloroprocaine | 2 | 10–20 | Rapid | 30–60 | 800 | Local infiltration or pudendal block | ||||||
| 3 | 10–20 | 30–60 | Epidural only for C-section | |||||||||
| Aminoesters† | ||||||||||||
| Bupivacaine | 0.25 | 5–10 | 60–90 | Epidural for labor | ||||||||
| 0.5 | 10–20 | Slow | 90–150 | 175 | Epidural for C-section | |||||||
| 0.75 | 1.5–2 | 60–120 | Spinal for C-section | |||||||||
| Lidocaine | 1–1.5 | 10–20 | Rapid | 30–60 | 300 | Local infiltration or pudendal block | ||||||
| 1.5–2 | 5–20 | 60–90 | Epidural for labor or C-section | |||||||||
| 5 | 1.5–2 | 45–60 | Spinal for D&C or puerperal tubal | |||||||||
| Ropivacaine | 0.2–0.5 | 5–10 | Slow | 60–90 | 200 | Epidural for labor | ||||||
| 0.5–1 | 10–30 | 90–150 | 250 | Epidural for C-section | ||||||||
In terms of neonatal outcomes, one study investigating the maternal and neonatal pharmacokinetics of lidocaine during labor, including in women receiving pudendal blocks, showed no clinically significant difference in the neonatal outcomes at 4 hours and 24 hours after delivery, regardless of the type of anesthetic used.6
