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Femoral block


Perspective

This block is useful for surgical procedures carried out on the anterior thigh, both superficial and deep. It is most frequently combined with other lower extremity peripheral blocks to provide anesthesia for operations on the lower leg and foot. As an analgesic technique, it is used for femoral fracture analgesia or for prolonged continuous catheter analgesia after surgery on the knee or femur.

Patient Selection. Because the patient is supine when this block is carried out, virtually any patient undergoing a surgical procedure of the lower extremity is a candidate. Because elicitation of paresthesia is not necessary to carry out femoral block, even anesthetized patients are candidates.

Pharmacologic Choice. As with all lower extremity blocks, a decision must be made about the extent of sensory and motor blockade desired. If motor blockade is necessary, higher concentrations of local anesthetic are needed. As with concerns about local anesthetic use in the sciatic block, the desire for motor blockade must be balanced against the volume of local anesthetic necessary if femoral, sciatic, lateral femoral cutaneous, and obturator blocks are combined. Approximately 20 mL of local anesthetic should be adequate to produce femoral block. With continuous catheter techniques used for postoperative analgesia, 0.25% bupivacaine or 0.2% ropivacaine may be used, and even lower concentrations of these drugs may be useful after a trial. With this technique, a rate of 8–10 mL per hour usually suffices.

Traditional block technique

Placement

Anatomy. The femoral nerve travels through the pelvis in the groove between the psoas and the iliacus muscles, as illustrated in Fig. 15.1 . It emerges beneath the inguinal ligament, posterolateral to the femoral vessels, as illustrated in Fig. 15.2 . It frequently divides into its branches at or above the level of the inguinal ligament.

Fig. 15.1, Femoral nerve anatomy: anterior oblique view.

Fig. 15.2, Femoral nerve anatomy: at inguinal ligament.

Position. The patient is in a supine position, and the anesthesiologist should stand at the patient’s side to allow easy palpation of the femoral artery.

Needle Puncture. A line is drawn connecting the anterosuperior iliac spine and the pubic tubercle, as illustrated in Fig. 15.3 . The femoral artery is palpated on this line, and a 22-gauge, 4-cm needle is inserted, as illustrated in Fig. 15.4 . The initial insertion should abut the femoral artery in a perpendicular fashion, as shown in Fig. 15.5 ( position 1 ); a “wall” of local anesthetic is developed by redirecting the needle in a fanlike manner in progressive steps to position 2 . (Ultrasonography highlights that the nerve is deep to the fascia iliaca, something difficult to appreciate without imaging guidance.) Approximately 20 mL of local anesthetic is injected incrementally in this fashion. It may also be useful to displace the needle entry site laterally 1 cm, direct the needle tip to lie immediately posterior to the femoral artery, and then inject an additional 2–5 mL of drug. This allows a block of those fibers that may be in a more posterior relationship to the femoral artery. Elicitation of paresthesia is variable with this block; however, if one does occur, the mediolateral injection should still be carried out because the nerve often divides into branches cephalad to the inguinal ligament.

Fig. 15.3, Femoral nerve block: skin markings for needle puncture.

Fig. 15.4, Femoral nerve block: needle puncture.

Fig. 15.5, Femoral nerve block: local anesthetic injection. The initial insertion abuts the femoral artery in a perpendicular fashion ( position 1 ); a “wall” of local anesthetic is developed by redirecting the needle in a fanlike manner in progressive steps to position 2 .

When using a continuous catheter technique, either stimulating catheter block kits, or traditional epidural needles and matched catheters may be used in adults ( Fig. 15.6 ). In the latter situation, the epidural needle is positioned either with the assistance of a nerve stimulator or with paresthesia elicitation as an endpoint. After the needle is positioned, 20 mL of preservative-free normal saline solution is injected through the needle, and then the appropriate-size catheter is inserted approximately 10 cm past the needle tip. Once the catheter has been secured with a plastic occlusive dressing, the initial bolus injection of the drug is carried out and the infusion is started.

Fig. 15.6, Femoral nerve block: use of continuous catheter.

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