52 Rectus Sheath Block

The rectus abdominis is a vertical muscle of the anterior abdominal wall. The muscle is divided into compartments by the midline linea alba, paramedian linea semilunaris, and transverse fibrous bands.¹ Muscles of the lateral abdominal wall (the external oblique, internal oblique, and transversus abdominis) become aponeurotic as they approach the midline. The rectus sheath consists of the rectus abdominis muscles surrounded by these aponeuroses.

Above the arcuate line, the transversalis fascia and the aponeuroses separate the rectus abdominis muscle from the abdominal cavity. Caudal to the arcuate line, the rectus abdominis muscle is in direct contact with the transversalis fascia. In this location, all three of the lateral abdominal wall muscles (external oblique, internal oblique, and transversus) have their aponeuroses pass anterior to the rectus abdominis muscle.²

Anterior cutaneous branches of the intercostal nerves enter the rectus sheath from the posterior and lateral sides.³ Epigastric arteries and veins are sometimes identified within the rectus sheath. The anterior intercostal nerves can run alongside these vessels before rising to the surface through the rectus abdominis muscle. The nerves of the rectus sheath are too small to be directly imaged with ultrasound.

Rectus sheath block is useful as part of a combined anesthetic technique for outpatients.^4,5 The usual indication for this block is to provide pain relief after repair of umbilical or incisional hernias. It provides an excellent alternative to straight general anesthesia or epidural blocks for surgical procedures around the midline of the abdominal wall.

Suggested Technique

The rectus sheath block is usually performed after induction of general anesthesia for patient comfort and to reduce movement. The choice of ultrasound transducer is not critical to the success of the procedure. With the patient in supine position, an in-plane approach from the lateral side of the patient is used, with the rectus abdominis muscle imaged in short-axis view (transverse). Hand-on-needle provides excellent needle control. Tidal movement of the abdominal cavity with respiration or contraction of the abdominal wall muscles can make the procedure challenging.

The goal is to have the injected local anesthetic layer underneath the rectus abdominis muscle where the anterior intercostal nerves enter the rectus sheath. The transversalis fascia and aponeurosis of the transversus muscle form a double-layer appearance on ultrasound scans. Therefore, the needle tip and injection should be placed between the rectus abdominis muscle and the double layer that constitutes the posterior aspect of the rectus sheath. To accomplish this view, the cephalocaudad placement of the transducer should be adjusted away from tendons to allow visualization of the double layer of the transversalis fascia.

Because the nerves enter the sheath from the lateral side, the lateral aspect of the rectus abdominis muscle is targeted. The lateral edge of the rectus sheath is a potentially safer approach because it is over the abdominal wall muscles rather than the abdominal cavity. Injection of a small volume of local anesthetic on pullback of the needle through the rectus abdominis muscle gives more complete distributions.

Because of the compartmental nature of the rectus abdominis muscle, two or four injections are usually performed for periumbilical surgery (right and left sides, and sometimes above and below the umbilicus). About 5 to 10 mL of local anesthetic is injected per side per compartment in adult patients. Because the tendinous inscriptions of the muscles are not complete posteriorly,⁶ some communication between compartments is possible. If local anesthetic is observed to distribute between compartments, no further injection is necessary.

The superior and inferior epigastric arteries anastomose through a vascular network. It is unlikely that large epigastric arteries will be found in the umbilical region because the contributing vessels course from above or below. Because of the lack of underlying bone, visible arterial pulsations are difficult to elicit with probe compression during rectus sheath blocks. Power Doppler can be useful during these procedures to confirm vascular identity.

In one study, 21% of rectus sheath injections guided by traditional loss-of-resistance techniques were intraperitoneal.⁷ These intraperitoneal injections were detected by ultrasound imaging after initial needle placement. Although no complications were observed in this study, intraperitoneal injections are not clinically effective and presumably place patients at risk for injury.

Key Points

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