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Identifying the different layers of the muscles is crucial because the peritoneum is the shiniest layer under the transversus abdominis muscle. When the bowels are seen under the peritoneum under ultrasound, the sliding sign appears in response to breathing.
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Loss of resistance when penetrating the different muscle layers can be felt as a pop. Extra caution is needed because the needle could advance accidentally into the peritoneum and perforate the bowel.
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Avoid puncturing the blood vessels, especially the inferior epigastric vessels, because they sometimes accompany the ilioinguinal and iliohypogastric nerves along their path. Ultrasound aids in visualizing these small vessels, especially if using Doppler mode.
Position
The patient is placed in the supine position with exposure of the abdominal and pelvic areas ( Fig. 44.1 ).
Anatomy
Identify the anterosuperior iliac spine (ASIS) and the umbilicus, and draw a line between these two points. Divide this line into three equal distances at the point where the outer one-third meets the inner two-thirds. This is the point of the needle entry. This point is about 2 cm medial and cephalad to the ASIS ( Fig. 44.2 ).
