Pudendal Anesthesia

CHAPTER 174 Pudendal Anesthesia



John J. Andazola, Dolores M. Gomez


Pudendal nerve anesthesia is a common nerve block technique used in obstetrics and minor gynecologic surgery. Its advantages include its safety, ease of administration, and rapidity of onset. Pudendal nerve block can be used to provide analgesia during the second stage of labor and to facilitate pelvic floor relaxation when using low forceps and vacuum extraction. It also provides anesthesia for the perineum in order to create or repair an episiotomy. Pudendal nerve anesthesia can be used for minor surgery of the lower vagina and perineum. Epidural anesthesia has largely supplanted the use of pudendal nerve anesthesia, but pudendal blocks are an alternative when neuraxial blockade is not feasible, not effective, or contraindicated. Although both transperineal and transvaginal approaches for pudendal blockade are options, the transvaginal approach is more practical and used most often. Therefore, only the transvaginal approach is discussed here.



Anatomy


The pudendal nerve supplies both sensory and motor innervation to the perineum. It is composed of parts of the second, third, and fourth sacral nerves and has three branches. In a woman, these branches supply the following structures:


1 The dorsal nerve of the clitoris, which innervates the clitoris and its erectile tissues

2 The perineal nerve, which innervates the muscles of the perineum and the skin of the labia minora, labia majora, and vestibule

3 The inferior hemorrhoidal nerve, which innervates the external sphincter of the anus and perianal skin (responsible for the anal “wink” reflex)

Pudendal anesthesia attempts to block the nerve as it enters the lesser sciatic foramen, usually inferior and medial to the insertion of the sacrospinous ligament on the ischial spine. The pudendal vessels lie lateral to the nerve at this location, so care must be taken to avoid intravascular injection. Although total block of the pudendal nerve should abolish pain and sensation over this entire area, there are other nerves that may also supply the sensory innervation to the perineum. Thus “skip” areas of analgesia may be noted, and complete nerve blockade can be ineffective on one or both sides as frequently as 50% of the time.



Indications



• Obstetric anesthesia for spontaneous vaginal delivery, episiotomy and episiotomy repair, repair of low vaginal lacerations, and low (outlet) forceps or vacuum-assisted delivery

• When epidural anesthesia is incomplete or inadequate

• For minor surgery of the lower vagina and perineum

NOTE: Because the upper vagina, cervix, and uterus receive separate innervation from the lower thoracic nerves, pudendal anesthesia alone is insufficient for midforceps application or for high vaginal, cervical, or uterine manipulation or repair.



Contraindications



Absolute



• Patient refusal

• Allergy to local anesthetic agents

• Current infection in the ischiorectal space or neighboring structures, including the vagina and perineum


Relative


Coagulopathy or anticoagulant therapy (e.g., warfarin, heparin or its analogs) or antiplatelet therapy (clopidogrel [Plavix]) is a relative contraindication for this procedure.



Equipment and Supplies



• Local anesthetic: 1% lidocaine (Xylocaine or generic) without epinephrine or 1% or 2% chloroprocaine (Nesacaine or generic; this may have lower toxicity than lidocaine but does not last as long)

• Iowa trumpet (Fig. 174-1A) or similar guide to facilitate placement of the needle

• 10-mL syringe with finger ring (Fig. 174-1B)

• Needle, usually 6-inch, 22-gauge (see Fig. 174-1B) (The operator should check, before the procedure, that the needle is longer than the guiding device and equipped with a “stop” to prevent penetration of tissue deeper than 10 to 15 mm.)

• Sterile gloves


image

image

Figure 174-1 A, Iowa trumpet and syringe with finger rings separated. B, Iowa trumpet and syringe with finger rings together.



Precautions


Care must be taken to avoid intravascular injection because the pudendal vessels lie lateral to the pudendal nerve. Toxicity may occur with 1% lidocaine without epinephrine (10 mg/mL) above 1 mg/kg (70 mg or 7 mL in a 70-kg patient) with intravascular administration. Maximum dosage should not exceed 4.5 mg/kg or a maximum of 30 mL of 1% solution (300 mg), and the maximum dose should not be repeated in less than 2 hours (see Chapter 4, Local Anesthesia, for maximum dosages). A successful pudendal block may impair some reflexive maternal pushing, which may prolong the second stage of labor in women who are ineffective at pushing.



Preprocedure Patient Preparation


Explain the potential risks (see the Contraindications and Complications sections) and the potential benefits to the patient so she may make an informed decision. This discussion should include alternatives and occur before the moment of greatest anesthetic need, when neither the patient nor the clinician can communicate optimally. Ideally, anesthesia should be decided as part of a birth plan, and this should be discussed and written well before the pregnancy is at term.

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May 14, 2017 | Posted by in GENERAL & FAMILY MEDICINE | Comments Off on Pudendal Anesthesia

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