A high-frequency transducer is preferred for this block.
The rectus sheath block provides periumbilical somatic analgesia from the levels T9–T11 and is used for surgeries involving a periumbilical incision.
The block is performed at or slightly above the level of the umbilicus to avoid injury to the deep epigastric artery.
Direct visualization of the nerves is not required to perform a successful rectus sheath nerve block; instead, identification of the fascial plane is paramount.
The branches of the thoracolumbar nerves do not cross midline; therefore in order to provide a bilateral block, a right and left rectus abdominis block is performed.
The rectus abdominis muscle receives sensorimotor innervation through thoracolumbar spinal segmental nerves from spinal levels T7–L1. These nerves travel in the fascial plane between the internal oblique and the transversus abdominis muscles to the anterior abdominal wall.
At the lateral border of the rectus abdominis, the aponeuroses of the external oblique, internal oblique, and transversus abdominis muscle combine to form the linea semilunaris. At this lateral aspect, the thoracolumbar spinal segmental nerves pierce through the rectus abdominis muscle and create a nerve plexus to provide motor and sensation to the rectus abdominis muscles ( Fig. 35.1 ). The common aponeurosis splits into an anterior and posterior aponeurosis that encase the rectus abdominis muscle and nerve plexus in a sheath.
The rectus sheath is composed of an anterior and posterior aponeurosis that bind the rectus abdominis muscle and form the rectus sheath. At midline, the anterior and posterior aponeuroses of the right and left rectus abdominis muscles combine to form the linea alba, a thick fibrous band of fascia. The thoracolumbar spinal nerves do not cross the linea alba; therefore a rectus sheath block requires a bilateral block or two separate catheters to be performed.
It is important to note the deep epigastric artery provides blood supply to the rectus abdominis muscle and enters the muscle body at the level of the arcuate ligament. To avoid this, the block should always be performed at or above the level of the umbilicus. Beneath the rectus sheath the peritoneal cavity can be appreciated with the presence of abdominal contents, which can usually be observed during the block.
With the patient in a supine position, a high-frequency, linear ultrasound probe is placed in a transverse position just lateral to the umbilicus ( Fig. 35.2 ). The lens-shaped rectus abdominis muscle is identified below the ultrasound transducer with attention to identify and avoid the deep epigastric artery during the procedure ( Fig. 35.3 ). The authors recommend sliding the probe lateral from this position to identify the linea semilunaris. This location allows for a more direct visualization of the posterior rectus sheath and a more superficial access to the posterior fascial plane ( Fig. 35.4 ). Direct identification of the intercostal nerves is not required in order to complete a successful rectus sheath block.