Pudendal nerve block can be used to supplement pain relief during the second stage of labor. The S2-S4 nerves give off branches to the pudendal nerve that pass between the pyriformis and coccygeal muscles. The nerve exits the pelvis through the greater sciatic foramen and reenters it again through the lesser sciatic foramen. The nerve then divides into three nerves: inferior rectal nerve which innervates the anal and perianal regions; dorsal nerve of the penis or the clitoris innervating the dorsum of the penis or clitoris; and perineal nerve which supplies muscles of the urogenital triangle, posterior 2/3 of the labia majora or posterior 2/3 of the scrotum in males.
Arrange sterile towels, sterile gloves, gauze pads, syringes, and needles for local infiltration and nerve block placement.
20 ml syringes of local anesthetic. Needles
20 g 6.0 in. needle for skin infiltration and a 22 g 5 cm short bevel insulated stimulation needle.
Surface Anatomy and Landmarks Landmarks
The pudendal nerve may be blocked by a transvaginal approach (A) or transperineal approach (B).
A. With the patient in the lithotomy position, the ischial spine is bracketed transvaginally by a hand in the vagina. A 20 g 6 in. needle is then inserted through the vaginal mucosa through the sacrospinous ligament and beyond the ischial spine. After negative aspiration, 10 cc of preservative-free lidocaine is injected and then another 3-4 cc can be injected as the needle is withdrawn to block the inferior rectal nerve.
B. The ischial tuberosity is identified with the patient in the lithotomy position. With aseptic technique, a 6-in. needle is inserted at a point that is 1 in. lateral and 1 in. posterior to the tuberosity and the needle is directed toward the ischial spine. After negative aspiration, a total of 10 cc of lidocaine is injected with another 3-4 cc of lidocaine injected as the needle is withdrawn to block the inferior rectal nerve.
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