Ovid: Peripheral Nerve Blocks: A Color Atlas

Ultrasound Guided Femoral Nerve Block

Anahi Perlas

Patient Position: Supine.

Indications: Surgery on the anterior thigh, femur, or knee. Block of the saphenous nerve tributary for surgery on the leg or foot.

Needle Size: 22-gauge, 5-cm stimulating needle.

Surface Landmarks: The inguinal crease.

Ultrasound Landmarks: The femoral artery and the femoral nerve. The nerve lies lateral or occasionally deep to the artery (Fig. 39-1).

Transducer Type: 10 to15 MHz linear array.

Transducer Position: The probe is located in the axial plane along the inguinal crease (Fig. 39-2).

Volume: 10 mL.

Technique: Sterile prep of the skin. The probe is placed just below the inguinal crease with the probe oriented in the axial plane. The femoral artery is identified and the hyperechoic nerve is identified lateral to the artery (Fig. 39-3). The needle is inserted at the lateral edge of the probe and advanced until a contraction is seen in the quadriceps femoris muscle. A stimulating current of 0.5 mA is usually appropriate to elicit a contraction (Fig. 39-4). Injection of local anesthetic proceeds until the nerve is surrounded by a hypoechoic ring (Fig. 39-5).

P.295

Figure 39-1. Gross anatomy of the femoral triangle together with a drawing or section of the femoral vessels and nerve in the transverse plane.

Figure 39-2. Transducer position.

Figure 39-3. Femoral artery and hyperechoic nerve.

P.296

Figure 39-4. A stimulating current is appropriate to elicit a contraction.

Figure 39-5. Injection of local anesthetic until the nerve is surrounded by a hypoechoic ring.

Figure 39-6. Catheter technique.

Tips

If a catheter technique is appropriate, the practitioner may wish to insert the needle perpendicular to the long axis of the probe (Fig. 39-6). This allows advancement of the catheter into the femoral sheath without an acute angulation. The needle is advanced toward the nerve and its tip is inferred by tissue distortion. Once a contraction has been elicited, local anesthetic may be injected and seen spreading around the nerve. The catheter is then inserted into the nerve sheath.