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Pudendal Block
A pudendal block provides excellent anesthesia to an area about the size
of a dinner plate, centered on the vagina.
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.
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. |
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.
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