July 15, 2006
Ultrasound Guided Femoral Nerve Block - A Solid Technique
I needed to update this page because I noticed that since it was about the first written, the information on it was generally the oldest. So where is the femoral nerve block technique now, after all this time?
The femoral nerve block performed under ultrasound guidance is the most common and reliable procedures we do at our institution. Most of the practitioners involved have do not use the nerve stimulator for the procedure, relying instead completely on the ultrasound to guide needle placement.
In general, the routine goes like this;
- Patient is identified and the surgical procedure and side is confirmed.
- The patient is consented, monitors attached and given light sedation.
- Position is supine with the operative leg slightly abducted.
- The groin on the operative side is prepped and ultrasound gel is placed above groin.
- The operator gloves up, stands at the patient side
- Operator picks up the ultrasound probe with the hand closest to the patient head, and places it on the patient groin at about the level of the inguinal ligament and locates the femoral artery and associated structures on ultrasound.
- Operator places a skin wheal of lidocaine over the target just lateral to the artery.
- Nerve block needle (22G short bevel needle with attached tubing) is inserted through the skin wheal and progress to the target is monitored on the ultrasound image.
- 25 mls of local solution (mepivacaine 0.8% & bupivacaine 0.3%) is divided between the 3 points of the target triangle (next to the artery, next to the artery -deep, lateral to the first point.
- Site is cleaned off with a towel.
- The operator places his hand on the patient’s knee and push down with light pressure then asks the patient to bend the knee. (this is a trial to see if the maneuver hastens the block onset by forcing open sodium channels and allowing the local to penetrate more quickly)
Usually the patient begins feeling a subtle difference if the anterior leg in about 6 - 8 minutes.
No nerve stimulator is used. The block invariably sets up during the case and the patient awakens with the block in place.
Sometimes the patient complains of some amount of pain in recovery room, after a little time passes it is possible to get enough accurate information from the patient to discover the source of the pain. This is usually found to be; posterior pain from a sciatic block which didn’t work or wasn’t done, mid to upper thigh pain from the tourniquet, back pain from positioning during the case, pain in some other part of the body unrelated to the surgery, or pain in upper-most part of the incision especially noticed during extreme flexion of the “Continuous Passive Motion” machine.
Occasionally the patient awakens with an incomplete block which continues to intensify over the next hour or so.
Many days, this routine is repeated several times a day with gratifyingly predictable results making the ultrasound guided femoral nerve block a mainstay of the regional block program.