Pudendal Block

Bilateral blockage of the pudendal nerve will result in complete anesthesia over the perineum (shown here), and lower third of the vagina.

The ischial spines are boney landmarks found on deep pelvic examination of the lateral and posterior vaginal walls.

Palpate the ischial spine with your fingertip.

Place the Iowa Trumpet along the length of the sacrospinous ligament, about one cm from it's insertion onto the ischial spine.

Using the Iowa Trumpet as a guide, insert the needle so that it perforates the sacrospinous ligament. Slowly infiltrating 10 cc of 1% lidocaine will effectively block the pudendal nerve as it courses (with the pudendal artery and vein) just beneath the sacrospinous ligament at this point.

This block will allow for numbing the vaginal opening to allow for a less painful delivery, some introital relaxation, and satisfactory anesthesia for repair of lacerations or episiotomies.

The perineum is innervated by the pudendal nerves that originate from S3-S4, and pass close to the ischial spine as it traverses the pelvic sidewall.

The ischial spines are boney landmarks palpable to the examining finger, and located deep, lateral and a little posterior to the vagina. The spine can be felt as a distinct boney "bump" quite separate from the rest of the pelvic sidewall.

Running from the ischial spine to the sacrum is the sacrospinous ligament, a tough band of tissue that can be felt with the examining fingers. This ligament is important because the pudendal nerve runs just underneath it and next to the ischial spine.

How to give a pudendal block
The essential equipment includes and "Iowa Trumpet," a long, hollow, blunt tube for placing at the injection site, and a matching needle, slightly longer. Pre-packaged kits typically will include both the Iowa Trumpet and the needle. Most kits will also have a plastic spacer on the needle that limits its depth of penetration to 5 mm beyond the Iowa Trumpet. This 5 mm depth of penetration is just right for a paracervical block, but is too shallow for a pudendal block. Remove the spacer  to allow for a full 10 mm depth of penetration.

Open the kit and put on sterile gloves. The injection is done by feel, not by visualization. Use your right hand to examine the patient, determine the cervical dilatation, location of the fetal presenting part, and the ischial spine on the patient's right side. Keeping two fingers of the right hand in the vagina, slide the Iowa Trumpet (without the needle) down the length of your vaginal fingers and direct it onto the sacrospinous ligament, about 1 cm from the ischial spine.

Once the trumpet is in place, slide the long needle through the Iowa Trumpet until it is fully seated within the trumpet. At this point, the tip of the needle will be extending 10 mm beyond the Iowa Trumpet and will have perforated through the sacrospinous ligament.

Aspirate to make sure you haven't perforated a blood vessel, then slowly inject 10 cc of 1% lidocaine.

Move to the opposite side. Switch vaginal examining hands so that the left hand is in the vagina when injecting on the left side of the patient. Repeat the procedure, injecting another 10 cc.

It will take 10-20 minutes to achieve maximum anesthesia effect after the injections are complete. One-sided blocks are common and can be treated with an additional 5 cc of lidocaine to the poorly-anesthetized side.