Figure 42–1. Anatomic relationship of the ilioinguinal and iliohypogastric nerves.

Of note, the ventral rami of the lower intercostal nerves (Til and T12) also pierce the transversus abdominis muscle to lie between it and the internal oblique. These latter nerves also supply sensation to the inferior abdominal wall, and block of these nerves as well as the iliohypogastric and ilioinguinal nerves is essential to provide anesthesia for procedures involving the lower abdominal wall.

METHOD OF BLOCK

Using the anatomic knowledge previously described, one needs to provide a method of block that allows accurate placement of local anesthetic between the internal oblique and external oblique muscles.

Methods of local anesthetic administration that do not accurately define placement between these muscular layers provide inconsistent anesthesia and analgesia of the abdominal wall and inguinal region. Unfortunately, this may result in the reporting of inadequate analgesia for a procedure that is more a problem of technique than of the block itself.⁶ Accurate block techniques must define the specific muscular layers of the abdominal wall. The only way to facilitate this is to use loss of resistance techniques that define fascial layers.

Initially, the anterior superior iliac spine is palpated and a mark made 2 cm medial and 2 cm superior from it (Figure 42–2). After skin preparation and infiltration with local anesthetic, a small puncture is made in the skin with a sharp needle to allow subsequent insertion of a blunt needle. The needle is inserted through the skin puncture site perpendicular to the skin. Increased resistance is met as the needle encounters the external oblique muscle. A loss of resistance is appreciated as the needle passes through the muscle to lie between it and the internal oblique. After the initial loss of resistance and negative needle aspiration for blood, 3 mL of local anesthetic is injected.

Figure 42–2. Surface landmarks for ilioinguinal block. The point of needle insertion is marked 2 cm medial and 2 cm superior from the anterior superior iliac spine (ASIS).

Figure 42–3. Needle maneuvers to block the iliohypogastric and ilioinguinal nerves. Shown is perpendicular needle insertion (1), lateral (2), and medial (3) redirections (fan technique).

The needle is then withdrawn to skin and redirected at a 45-degree angle medially to again pierce the external oblique muscle (Figure 42–3). After loss of resistance, 3 mL of local anesthetic is again administered. The needle is then returned to skin and inserted 45 degrees laterally, and the procedure is repeated. Thus, a total of 9 mL of local anesthetic is placed in a fan-like distribution between the external and internal oblique muscles.

After completion of the block, the skin of the lower abdominal wall or inguinal region is tested for anesthesia.

Equipment

Any atraumatic needle blunt enough to appreciate a loss of resistance is used for this block. Examples are 22-gauge Whitacre, Sprotte, 18-gauge Tuohy-type(which can also be used to place catheters), 21-gauge Stimuplex needles, etc.

INDICATIONS & CONTRAINDICATIONS

Indications for ilioinguinal/iliohypogastric blocks include anesthesia for any somatic procedure involving the lower abdominal wall/inguinal region such as inguinal herniorrhaphy^2–5 and for analgesia after surgical procedures using a Pfannenstiel incision as for cesarean section⁷

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