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

Rectus Sheath Block	The Essentials
Anatomy	The nerves of the rectus sheath enter the posterolateral side of the RA.
	The TA lies under the lateral aspect of the RA in the supraumbilical region.
	Epigastric arteries and veins usually lie deep within the midportion of the RA.
	Tendinous intersections divide adjacent rectus sheath compartments.
	These tendons are thought to be incomplete posteriorly.
	This should allow communication between adjacent compartments.
Positioning	Supine
Operator	Standing on the side of the patient
Display	Across the table
Transducer	High-frequency linear, 38- to 50-mm footprint
Initial depth setting	35 to 50 mm
Needle	20 to 21 gauge, 70 to 90 mm in length
Anatomic location	Begin by scanning the RA in transverse view.
	Slide transducer to midway between the tendinous intersections.
Approach	Transverse view of RA, in-plane from lateral to medial.
	Aim for the posterolateral corner of the RA.
	Place the needle tip between the RA and underlying fascial double layer.
	If necessary, scratch the needle tip against the fascial double layer.
	Bilateral injections are necessary for midline anesthesia.
Sonographic assessment	Desire side-to-side (medial-lateral) distribution over the double layer.
	“Swimming pool” or “smile” shaped appearance of distribution between RA and double layer.
	Desire cephalocaudad distribution between adjacent compartments.
	The “handlebar mustache” appearance of the longitudinal distribution between compartments.
Anatomic variation	Position of epigastric arteries and TA varies.

RA, Rectus abdominis muscle; TA, transversus abdominis muscle.

Clinical Pearls

• The extent to which the abdominal wall muscles underlie the lateral corner of the rectus abdominis muscle is variable. In some cases there is no underlying muscle to separate the rectus from the abdominal cavity.

• The needle tip should be scratched against the double layer but not actually puncture it so as to place the tip between the rectus muscle and the double layer.

• A few milliliters of local anesthetic can be injected as the needle is removed to cover the path of nerves through the rectus muscle.

• The best way to perform rectus sheath blocks is to inject forward on one side and back for the contralateral side. In this fashion the ultrasound display screen and operator remain in one position for bilateral injections.

• The fibers of the rectus abdominis course in a parallel direction, with the muscle divided by transverse tendinous intersections.

• The nerves of the rectus sheath are too small (100 µ diameter) to be directly imaged with ultrasound.³ Therefore, ultrasound-guided rectus sheath block relies on injecting between the rectus abdominis muscle and the underlying double layer of fascia at the point where the nerves are known to enter the rectus sheath.

• The rectus abdominis muscle is slightly narrower near its ends at the xiphoid process and pubic bone. The rectus sheath narrows at its cephalad and caudad ends as the linea semilunaris tapers toward the midline.

FIGURE 52-1 Thoracoabdominal nerves. Note the path of the anterior cutaneous branch of the intercostal nerve through the rectus abdominis muscle.

(From netterimages.com, with permission.)

FIGURE 52-2 External photograph showing the approach to rectus sheath block in supine position. An in-plane approach from across the midline is shown (A). The corresponding sonogram in shown (B). The best way to perform rectus sheath blocks on both sides of the midline is to inject forward on one side compartment and back for the opposite side, with the screen and operator in one position.

FIGURE 52-3 The double-layer sign indicating presence of the aponeurosis of the transversus abdominis and transversalis fascia in transverse view (A). Closer to the midline, loops of bowel are visualized (B).

FIGURE 52-4 The epigastric arteries have variable position within the rectus sheath. In these examples from different patients, the arteries are seen either below (A) or within (B) the rectus sheath in transverse view.

FIGURE 52-5 The transversus muscle on the lateral edge of the rectus abdominis in transverse view. The extent to which the abdominal wall muscles underlie the lateral corner of the rectus abdominis muscle is variable. In some cases, there is no underlying muscle to separate the rectus from the abdominal cavity.

FIGURE 52-6 Longitudinal views of the rectus abdominis muscle within a single muscular compartment (A) and in separate rectus compartments (B). The fibers of the rectus abdominis course in a parallel direction, with the muscle divided by transverse tendinous intersections that are typically incomplete posteriorly.

FIGURE 52-7 Image sequence showing rectus sheath block. An in-plane approach is demonstrated where the needle tip is placed between the rectus muscle and the double layer (A). Before injection, the needle tip is gently scratched against the double layer so as to place the tip between the rectus muscle and the double layer. Local anesthetic is seen to layer underneath the muscle, giving a swimming pool appearance of successful rectus sheath injection in transverse view. A few milliliters of local anesthetic can be injected as the needle is removed to cover the path of nerves through the rectus muscle. The corresponding longitudinal view is shown (B).

FIGURE 52-8 Image sequence showing rectus sheath block. Before needle tip placement, the double layer is identified (A). An in-plane approach is demonstrated where the needle tip and local anesthetic are placed between the rectus muscle and the double layer (B). After rectus sheath injection, longitudinal views can be used to assess the distribution (C). The handlebar mustache appearance verifies that local anesthetic has distributed to the adjacent compartment of the rectus abdominis muscle.