Ultrasound Blocks for the Anterior Abdominal Wall

4. Iliohypogastric and Ilioinguinal Nerve Block | 45
4. the point 10–20 mm medial and 10–20 mm superior to the
ASIS
5. the point just 10 mm medial to the ASIS
6. one finger-breadth medial to the ASIS, 5 cm above and
lateral to the mid-inguinal point
The last approach is mostly used for children and the measure
of the finger’s breadth is taken at the proximal inter-phalangeal
joint of the child’s ipsilateral index finger. Single or multiple
injections may be done and different puncture sites provide
similar effectiveness (Lim 2002).
The fascia between the EOM and the IOM offers a first
resistance to the needle felt as a “pop” or “ting” or “ping”,
whereas the fascia between the IOM and the TAM provides a
second resistance. After the second resistance has been felt, the
local anesthetic may be injected.
This ‘resistance’ may be very subtle, particularly in small
infants and thin children. A useful tip is to hold a skin fold
between the thumb and index of one hand and puncture the skin
to reach the subcutaneous tissue. The first ‘pop’ felt is likely to
be the aponeurosis of the EOM (Frigon 2006). Another way is to
use a sharp introducer to puncture the skin. A 22G Whitacre
spinal needle inserted through the introducer into the
subcutaneous tissue will provide a good feedback in terms of a
distinct ‘pop’ as the EOM aponeurosis and the IOM fascia are
penetrated.
However, anatomic and ultrasound control studies on the
classical landmarks show that only two muscle layers instead of
three may be identified in 50% of the patients. This occurs
because the EOM is limited to an aponeurosis in the medial area
adjacent to the ASIS (Willschke 2005).