The rectus sheath block is a useful technique for umbilical surgery, particularly in pediatric patients. Ultrasound guidance allows for a greater reliability in administering local anesthetic in the correct plane and decreasing the potential for complications. The placement of the needle is in the proximity to the peritoneum and the epigastric arteries. Guiding the needle under ultrasound guidance to the posterior rectus sheath rather than relying on “pops,” such as in the traditional, non-ultrasound techniques, makes this block more reproducible and reduces the risk of inadvertent peritoneal and vascular punctures.
The rectus abdominis muscle is oval shaped, positioned under the superficial fascia of the abdomen. Laterally, the aponeurosis of the external oblique, internal oblique and transversus abdominis muscles split to form two lamellae that surround the muscle anteriorly and posteriorly (forming the rectus sheath), before rejoining again in the midline to insert on the linea alba (Figures 42.3-1A and B). The 9th, 10th, and 11th intercostal nerves are located in the space between the rectus abdominis muscle and its posterior rectus sheath, although they are usually difficult to depict sonographically. Color Doppler reveals small epigastric arteries in the same plane. Deep to the rectus sheath is preperitoneal fat, peritoneum, and abdominal content (bowel), which can usually be observed moving with peristalsis.
FIGURE 42.3-1. (A) Ultrasound anatomy of the rectus abdominis sheath. (B) Labeled Ultrasound anatomy of the rectus abdominis sheath. RAM, rectus abdominis muscle.
Distribution of Blockade
Blockade of the nerves of the rectus sheath results in anesthesia of the periumbilical area (spinal dermatomes 9, 10, and 11). It is a rather specific, limited region of blockade, hence its specific indications.
Equipment needed is as follows:
• Ultrasound machine with linear transducer (6–18 MHz), sterile sleeve, and gel
• Standard nerve block tray
• 20-mL syringe containing local anesthetic
• 50-100 mm, 22-gauge short-bevel needle
• Sterile gloves
Landmarks and Patient Positioning
Typically this block is performed in the supine position.
The goal is to place the needle tip just posterior to the rectus muscle but anterior to the posterior rectus sheath. Once the needle tip is positioned correctly, local anesthetic is deposited between the muscle and posterior rectus sheath, and correct spread is confirmed on ultrasound. An additional aliquot of local anesthetic is injected just posterior to the sheath.
With the patient in supine position, the skin is disinfected and the transducer placed at the level of the umbilicus immediately lateral, in transverse position (Figure 42.3-2). Color Doppler can be used to identify the epigastric arteries so that their puncture can be avoided. The needle is inserted in-plane in a medial to lateral orientation, through the subcutaneous tissue, to pearce through the anterior rectus sheath (Figure 42.3-3). Out-of-plane technique is also suitable and often preferred in obese patients. The needle is further advanced through the body of the muscle until the tip rests on the posterior rectus sheath. After negative aspiration, 1 to 2 mL of local anesthetic is injected to verify needle tip location (Figure 42.3-4). When injection of the local anesthetic appears to be intramuscular, the needle is advanced 1 to 2 mm and its position is checked by injection of another aliquot of local anesthetic. This is repeated until the correct needle position is achieved. When a large volume of local anesthetic is planned (e.g. in combining billateral TAP and rectus abdominis sheath blocks), the described “hydro-disection” for the purpose of localization of the needle tip can be done using 0.9% saline or chlorprocaine to decrease the total mass of the more toxic, longer acting local anesthetic.
FIGURE 42.3-2. Transducer position and needle insertion to accomplish rectus sheath block.
FIGURE 42.3-3. Simulated needle path (1) to accomplish the rectus sheath block. Needle tip is positioned between the posterior aspect of the rectus abdominis muscle (RAM) and the rectus sheath (posterior aspect).
FIGURE 42.3-4. Simulated needle path (1) and spread of local anesthetic (blue shaded area) to accomplish the rectus sheath block. Local anesthetic should spread just underneath and within the posterior aspect of the rectus sheath. RAM, rectus abdominis muscle.
• An out-of-plane technique can also be used directly through the belly of the rectus muscle. Because the needle tip may not always be seen throughout the procedure, small boluses of local anesthetic are injected as the needle is advanced toward the posterior rectus sheath, confirming the correct position of the needle tip.
In an adult patient, 10 mL of local anesthetic (e.g., 0.5% ropivacaine) per side is usually sufficient for successful blockade. In children, a volume of 0.1 mL/kg per side is adequate for effective analgesia.
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