ANATOMY
The anterior abdominal wall consists of 5 paired muscles: 2 vertically orientated muscles, one on either side of the midline, and 3 flat muscle layers located laterally.
The 3 flat muscles consist of 3 stacked layers: transversus abdominis (innermost layer), internal oblique (middle) and external oblique muscles (outermost layer).
Medially these muscles form aponeuroses to form the rectus sheath and connect in the midline to form the linea alba, a fibrous structure that extends from the xiphoid process to the pubic symphysis.
Either side of the linea alba, long rectus abdominis muscles run between xiphoid process to the pubic bone caudally. The lateral border forms the linea semilunaris, parallel to the midline. The rectus abdominus muscle is intersected anteriorly by fibrous strips, known as tendinous intersections; creating the “six-pack” appearance.
The rectus sheath envelopes the muscle anteriorly and posteriorly. Posteriorly, at the level of the arcuate line, the sheath disappears, and the muscle is in direct contact with the transversalis fascia.
Anterior rami of the nerves from T6-L1 exit the intercostal space and run in the fascial plane between internal oblique and transverse abdominis muscles. They pierce the posterior rectus sheath, traverse the rectus abdominus muscle and enter the anterior rectus sheath to supply sensation to the anterior abdominal wall.
The rectus sheath block is directed at the posterior wall of the rectus sheath. Here the transverse tendinous intersections (six-pack) seen on the anterior surface of the rectus abdominis are absent which allows the local anaesthetic to flow freely along the vertical length of the muscle
This block is usually performed bilaterally as the nerves cross over the midline
PATIENT POSITION
Supine
NOTE: Use the larger linear probe for all age groups, except for neonates (you can use a smaller probe). You will have a longer needle trajectory, but this allows for more accurate needling and ensures a very shallow needle trajectory. It can also facilitate the performance of both blocks without the need to move the probe and reconfirm the anatomy in smaller children
SONOANATOMY
Ultrasound probe selection: linear high frequency probe
NEEDLING
Use a 50-60mm block needle
Target depth: 0.1-5cm
NOTE: Repeat the procedure for the opposite side to give bilateral rectus sheath blocks
NOTE: Can be performed on multiple levels if needed, beware of the maximal LA dose and dilute if necessary
NOTE: In neonates use NaCl 0.9% to confirm needle tip position before wasting LA, dilute LA to increase volume and spread
Levobupivacaine 0.25% 0.1-0.3ml/kg each side (+/- clonidine 1mcg/kg for increased duration)
NOTE: When inserting rectus sheath catheters:
