17 Lower Limb
Analgesia of the entire leg can be achieved through a combined block of the femoral nerve and the sciatic nerve. An advantage of this combined block is the significantly longer effect compared to caudal anesthesia.
17.1 Femoral Nerve Block
The anatomy is described in Chapter 10.
A linear transducer is placed directly caudal and parallel to the inguinal ligament (Fig. 17.1). The femoral neurovascular bundle is visualized in the short axis.
In the short axis, the femoral nerve has an oval shape and appears hyperechoic with hypoechoic fascicular (“honeycomb-like”) internal structure (Fig. 17.2). The femoral nerve is usually directly lateral to the femoral artery. The fascia lata is very echogenic and runs at the top of the ultrasound image, closer to the transducer than the nerve and vessels. The iliac fascia can be seen as a delicate hyperechoic band immediately above the femoral nerve (Fig. 17.2) surrounding the iliopsoas muscle and the nerve. The femoral nerve is usually located in the angle between the artery and the iliac fascia, from which it can be well defined by controlled transducer pressure.
Below the nerve, more distant to the probe, runs the iliopsoas muscle. It can be identified by its typical hypoechoic structure.
17.1.3 Technique of Femoral Nerve Block
Inguinal ligament, femoral artery, and iliac fascia in the ultrasound image.
The child is positioned supine; the affected leg is externally rotated and slightly abducted.
The inguinal ligament is palpated and the transducer is placed parallel and just distal to the inguinal ligament (Fig. 17.1). After sonographic identification of the femoral nerve located lateral to the artery in the short axis (Fig. 17.2) the region is disinfected, draped, and a sterile sleeve is placed in the transducer. The transducer is placed again at the previously determined position.
For a catheter technique, an out-of-plane needle direction is particularly suitable (Fig. 17.1); for a single-shot method, either an out-of-plane or an in-plane technique may be used.
After a stab incision with a lancet, the regional anesthesia needle is advanced toward the nerve under repeated aspiration. After negative aspiration, the local anesthetic is spread around the nerve so that the nerve is surrounded as completely as possible.
If a continuous technique is planned, the catheter is then advanced 2 to 3 cm beyond the tip of the needle.
Local Anesthetic, Dosage
Administration of 0.5 to 1 mL/kg body weight of a long-acting local anesthetic (e.g., ropivacaine 0.2–0.5% [2–5 mg/mL]), maximum 20 mL.
The maximum permissible local anesthetic dose per kilogram body weight must not be exceeded!
Give infants, toddlers, and children older than 6 months a maximum 0.4 mg/kg per hour of ropivacaine.