Ilioinguinal and Iliohypogastric Nerve Blocks

Fig. 31.1

Surface anatomy for ilioinguinal nerve block

Alternatively, the puncture site is considered at a point one fingerbreadth (of the patient) medial and inferior to the ASIS (the lower range for infants and young children) [2, 3].

In a study of ultrasonographic imaging during ilioinguinal block, the ilioinguinal nerve was situated between 5 and 11.3 mm from the ASIS, depending on the weight of the child, although there was no significant correlation between weight and this distance [4].

Any one of these points may be suitable, although in general, there is much variation in the nerves’ locations, and ultrasound guidance is recommended for optimizing localization.

A 3–4 cm, short-beveled or facet tipped, 22G–27G needle is inserted at a 45° angle to the midline at the puncture point (2.5 mm along the line between the ASIS and the umbilicus) until the characteristic “click” is detected after internal oblique muscle penetration.

However, the author prefers to insert the needle perpendicularly at only one patient’s fingerbreadth medial to the ASIS; this technique should reduce the risk of inadvertent bowel perforation.

Although two “clicks” may be experienced upon crossing the external and internal oblique muscles, one “click” is often detected. In many patients, the external oblique muscle has already turned into an aponeurosis at this level.

31.2.4 Local Anesthetic Application

Ensure negative aspiration prior to injecting local anesthetic.
Inject local anesthetic (typically 0.3–0.5 mL/kg of 0.25 % levobupivacaine or 0.5 % bupivacaine when using “blind” technique) after detecting the fascial “click” upon penetration of the internal oblique muscle. A fanlike injection pattern, with both cephalad (toward the umbilicus) and caudad (toward the groin) directions, has been described.
Alternatively, this author prefers to maintain the needle perpendicular to the skin while injecting one-third of the local anesthetic injection upon feeling the second “click” (internal oblique fascia), withdrawing the needle slightly and injecting another one-third above this layer, and then withdrawing slightly again and injecting the remaining one-third above the first “click” (external oblique fascia).
An initial injection of some of the local anesthetic may be performed subcutaneously prior to advancing the needle to the intermuscular plane.
Upon withdrawal of the needle, an additional 0.5–1 mL is deposited subcutaneously to ensure blockade of the iliohypogastric nerve.

31.3 Nerve Stimulation Technique

Nerve stimulation is not commonly performed for ilioinguinal nerve blocks.

31.4 Ultrasound-Guided Technique

The ilioinguinal nerve and surrounding musculature are depicted in the MRI and corresponding ultrasound images in Fig. 31.2. Prepare the needle insertion site and skin surface with antiseptic solution. Prepare the ultrasound probe surface by applying a sterile adhesive dressing to it prior to needling as discussed in Chap. 4.

Fig. 31.2

(a) VHVS and MRI images showing the ilioinguinal nerve and surrounding musculature. (b) Ultrasound images showing the ilioinguinal nerve and surrounding musculature

31.4.1 Scanning Technique

A linear (6–15 MHz) transducer is placed in an oblique location parallel to a line connecting the ASIS to the umbilicus.
A curved probe may be used in obese patients, but the muscle and fascial layers will likely be more difficult to appreciate.
The required depth for penetration is usually 1–4 cm but varies with the depth of the subcutaneous layer.
The layers of the abdominal wall and underlying muscles, as well as bone and target nerves, should be able to be identified in children.

31.4.2 Ultrasonographic Appearance

The layers of the abdominal wall should be visible, namely: skin, adipose tissue, external and internal oblique and transversus abdominis, peritoneum, and underlying bowel. The iliacus muscle and the ilium will be visible deeper to the working depth.
The external oblique may in 50 % of patients be aponeurotic in this location [4].
If the spermatic cord or round ligament is visible, then the probe is too medial and distal.
The ilioinguinal and iliohypogastric nerves are usually in proximity to each other.
The ilioinguinal and iliohypogastric nerves will be visible in children either between the external oblique and internal oblique or between the internal oblique and transversus abdominis muscle. The nerves are likely to much more difficult to appreciate in adults but may become more visible by using some fluid as contrast.
Color flow Doppler may assist in identifying the neurovascular bundle; however, it is often too small to visualize.
The endpoint for the block is to surround the identified ilioinguinal and iliohypogastric nerves with local anesthetic. Alternatively, if the nerves are not visible, for example, in adults or obese children, place local anesthetic in the TAP plane as well as the plane between the internal and external oblique muscles.