Femoral Block

Published on 06/02/2015 by admin

Filed under Anesthesiology

Last modified 22/04/2025

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13 Femoral Block

David L. Brown, with contributions from Brian D. Sites, Brian C. Spence

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 to 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 Figure 13-1. It emerges beneath the inguinal ligament, posterolateral to the femoral vessels, as illustrated in Figure 13-2. It frequently divides into its branches at or above the level of the inguinal ligament.

Figure 13-1. Femoral nerve anatomy: anterior oblique view.

Figure 13-2. 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.

A line is drawn connecting the anterior superior iliac spine and the pubic tubercle, as illustrated in Figure 13-3. The femoral artery is palpated on this line, and a 22-gauge, 4-cm needle is inserted, as illustrated in Figure 13-4. The initial insertion should abut the femoral artery in a perpendicular fashion, as shown in Figure 13-5 (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 to 5 mL of drug. This allows 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.

Figure 13-3. Femoral nerve block: skin markings for needle puncture.

Figure 13-4. Femoral nerve block: needle puncture.

Figure 13-5. Femoral nerve block: local anesthetic injection.

When using a continuous catheter technique, either stimulating catheter block kits or traditional epidural needles and matched catheters may be used in adults (Fig. 13-6). In the latter situation, the epidural needle is positioned either with the assistance of a nerve stimulator or with paresthesia elicitation as an end point. 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 drug is carried out and the infusion is started.

Figure 13-6. Femoral nerve block: use of continuous catheter.

Potential Problems

Patients with peripheral vascular disease often require unilateral lower extremity block; thus, a number of patients with prosthetic femoral arteries may be suitable candidates for this block. If lower extremity peripheral regional block has been chosen in a patient who has recently undergone placement of a prosthetic femoral artery, efforts should be made to avoid the prosthesis.

Pearls

Because a traditional block is actually a field block, enough “soak time” must be allowed to produce satisfactory anesthesia. When sciatic and femoral blocks are combined, it is often helpful to place the femoral block before the sciatic block, thus allowing extra soak time. Increasingly, patients undergoing surgery on the knee are effectively being offered femoral block as part of the postoperative analgesia regimen. Most often this is provided as a single-shot technique; however, some practitioners provide the analgesia using a continuous catheter method.

Ultrasonography-Guided Technique

The transducer should be placed in the infrainguinal region (Fig. 13-7) with the goal of imaging the femoral artery in its true short axis (i.e., it appears as a complete circle). If the patient is obese or there is difficulty locating the femoral artery, engaging the Doppler function may help in locating the femoral artery as a pulsatile structure.

Figure 13-7. Ultrasonography-guided femoral nerve block: transducer positioning.

Once the artery has been located, the nerve can be identified as an oval hyperechoic structure lying just lateral to the artery (Fig. 13-8). A key structure to identify is the fascia iliaca, which appears as a hyperechoic line extending off the iliopsoas muscle. The local anesthetic must be injected below the fascia iliaca to generate an effective block.

Figure 13-8. Ultrasonography-guided femoral nerve block: femoral nerve (FN) as hypoechoic structure. FA, femoral artery; IPM, iliopsoas muscle.

The needle is inserted at a roughly 45-degree angle using the in-plane technique, as depicted in Figure 13-7. The primary objective for this block is to visualize the needle or needle-related motion puncturing below the fascia iliaca and adjacent to the femoral nerve (see Fig. 13-7). There is a characteristic spread of local anesthetic (Fig. 13-9; see Fig. 13-8), which confirms correct needle tip location (see Video 10: Femoral Nerve Block: Correct Spread of Local Anesthetic Under the Fascia Iliaca on the Expert Consult Website).