BLOCKS OF NERVES SUPPLYING THE TRUNK

Ilioinguinal and Iliohypogastric Nerve Blocks

The iliohypogastric and ilioinguinal nerves are terminal branches of the lumbar plexus, and both originate from the first lumbar spinal nerve. The iliohypogastric nerve emerges from the lateral border of the psoas, perforates the transversus abdominis muscle, and runs obliquely adjacent to the posterior aspect of the internal oblique muscle. Near the iliac crest, the nerve divides into two terminal cutaneous branches: lateral, supplying the buttock, and medial, which crosses the external oblique muscle and supplies the abdominal wall above the pubis. The ilioinguinal nerve has a similar course, running below the iliohypogastric nerve. It crosses the quadratus lumborum and the iliacus muscle obliquely, pierces the transversus abdominis (at the level of the iliac crest), crosses the internal then the external oblique muscles, and finally reaches the lower border of the spermatic cord or the round ligament of the uterus within the inguinal canal. It provides sensory innervation to the upper medial part of the thigh and the upper part of the scrotum and penis or the labia major and the mons pubis. At the level of the medial part of the anterior wall of the abdomen, the ilioinguinal and iliohypogastric nerves lie in the same fascial plane at the inner surface of the superficial aponeurosis of the external oblique muscle. This fascial plane is also traversed by the genital branch of the genitofemoral nerve that supplies the spermatic cord. In this area, all three nerves can be anesthetized by a single injection of local anesthetic at the inner surface of the superficial fascia of the external oblique muscle.

The patient is placed in the dorsal recumbent position. The landmarks are the umbilicus and the anterior superior iliac spine.^{[261] [262]} The site of puncture is located at the union of the lateral one fourth with the medial three fourths of the line joining the anterior superior iliac spine to the umbilicus ( Fig. 45-19 ). A short and short-beveled needle is inserted at a 45- to 60-degree angle, pointing to the midpoint of the inguinal ligament, until the superficial layer of the external oblique muscle is pierced with a clearly identifiable "crack" (the piercing is sometimes difficult), and then a single injection of 0.3 to 0.4 mL of 0.25% bupivacaine is made in a fan-shape manner. With this insertion route, the tip of the needle pierces the fascia at a level where the ilioinguinal, the iliohypogastric, and the genital branch of the genitofemoral nerves have crossed the fascia covering the internal oblique muscle. The quality of analgesia can

Figure 45-19 Iliohypogastric and ilioinguinal nerve blocks, with the sites indicated for the umbilicus (1), anterior iliac crest (2), and pubic spine (3).

Alternate techniques have been described. The classic approach used two sites of puncture, including one potentially dangerous site at the level of the public tubercle, and three fascial planes had to be identified; its failure rate was rather high.^[265] Intraoperative infiltration of the hernial sac (which is the same technique) effectively relieves postoperative pain^[266] but does not protect against intraoperative pain.

With the technique described here, the ilioinguinal or iliohypogastric nerve block is easy to perform and virtually free of true complications. Undesired nerve blocks (especially femoral nerve blocks) are occasionally observed, especially when too much local anesthetic is injected, because of the spread of the local anesthetic caudad to the inguinal ligament. The only problem with this undesired effect is that it can delay the discharge of the patient by a few hours.