Lumbar plexus block

Perspective

The inguinal perivascular block is based on the concept of injecting local anesthetic near the femoral nerve in an amount sufficient to track proximally along fascial planes to anesthetize the lumbar plexus. The three principal nerves of the lumbar plexus pass from the pelvis anteriorly: the lateral femoral cutaneous, the femoral, and the obturator nerves. As illustrated in Fig. 13.1 , the theory behind this block presumes that the local anesthetic will track in the fascial plane between the iliacus and the psoas muscles to reach the region of the lumbar plexus roots.

Patient Selection. As outlined, lower extremity block is often most effectively and efficiently performed with neuraxial blocks. Nevertheless, in some patients avoidance of bilateral block or sympathectomy may make an alternative approach necessary.

Pharmacologic Choice. Local anesthetics should be selected by deciding whether a primarily sensory or a sensory and motor block is needed. Any of the amino amides can be used. It has been suggested that the volume of local anesthetic needed for adequate lumbar plexus block from this approach can be estimated by dividing the patient’s height, in inches, by three. That number is the volume of local anesthetic in milliliters that theoretically will provide lumbar plexus block.

Placement

Anatomy. The concept behind this block is that the only anatomy one needs to visualize is the extension of sheath-like fascial planes that surround the femoral nerve.

Position. The patient should be placed supine on the operating table with the anesthesiologist standing at the patient’s side in position to palpate the ipsilateral femoral artery.

Needle Puncture. A short-beveled, 22-gauge, 5-cm needle is inserted immediately lateral to the femoral artery, caudal to the inguinal ligament in the lower extremity to be blocked. It is advanced with cephalad angulation until femoral paresthesia occurs; alternatively, nerve stimulation or ultrasonographic guidance is used to identify the correct perineural location of the needle tip. At this point, the needle is firmly fixed, and while the distal femoral sheath is digitally compressed, the entire volume of local anesthetic is injected.

Potential problems

Our clinical experience suggests that the principal problem with this technique is a lack of predictability. In addition, whenever a large volume of local anesthetic is injected through a fixed “immobile” needle, the risk of systemic toxicity is increased. If the technique is used, incremental injection of local anesthetic, accompanied by frequent aspiration for blood, should be carried out.