Background
The transverse abdominis plane (TAP) block is a peripheral nerve block designed to anesthetize the nerves supplying the anterior abdominal wall (T6 to L1). It was first described in 2001 by Rafi as a traditional blind landmark technique using the lumbar triangle of Petit (see the image below). [1]
Local anesthetic is then injected between the internal oblique and transverse abdominis muscles just deep the fascial plane between (the plane through which the sensory nerves pass; see the images below).
Cross-section of the abdominal wall layers. The TAP block is performed by deposition of local anesthetic between the transversus abdominis muscle and the fascial layer superficial to it.
Illustration depicting the placement of the ultrasound probe along the abdominal wall, and the ideal placement of local anesthetic.
In a recent meta-analysis, the TAP block was shown to reduce the need for postoperative opioid use, increase the time to first request for further analgesia, and provide more effective pain relief, while decreasing opioid related side effects such as sedation and postoperative nausea and vomiting. [2] Studies included a combination of both general abdominal and gynecologic procedures. [3, 4] The introduction of ultrasound has allowed providers to identify the appropriate tissue plane and perform this block with greater accuracy under direct visualization. [5]
Indications
The TAP block is a simple procedure that can be used as an adjunct for postoperative pain control in abdominal, gynecologic [6] , or urologic surgery involving the T6 to L1 distribution. [1, 3, 4, 5] Surgical procedures investigated by randomized clinical trials include large bowel resection, caesarean delivery, abdominal hysterectomy, open appendectomy, and laparoscopic cholecystectomy. [1, 7]
However, the TAP block has also found clinical utility in procedures such as abdominal and inguinal hernia repair [8] , radical prostatectomy, nephrectomy [9] , and many different laparoscopic procedures in general. [10] Bilateral TAP blocks can be used for midline incisions. This technique is also useful for procedures in which epidural analgesia is contraindicated (ie, anticoagulated patients). In addition, if prolonged analgesia is desired, a continuous TAP block technique with placement of a catheter has been described. [11]
Contraindications
Very few contraindications exist to performing a TAP block. Absolute contraindications include infection at the site of injection, patient refusal or inability to cooperate, and allergy to local anesthetics.
Relevant Anatomy
The abdominal wall is composed of 5 paired muscles: 2 vertical muscles (the rectus abdominis and the pyramidalis) and 3 layered, flat muscles (the external abdominal oblique, the internal abdominal oblique, and the transversus abdominis muscles).
The internal abdominal oblique muscle is the intermediate layer of the 3 paired, flat abdominal muscles. It originates broadly from the anterior portion of the iliac crest, lateral half of the inguinal ligament, and thoracolumbar fascia. The internal abdominal oblique inserts on the inferior border of the 10th-12th ribs, the linea alba, and the pubic crest via the conjoint tendon. The muscle fibers of the internal abdominal oblique course upward in a superomedial orientation, perpendicular to the muscle fibers of the external abdominal oblique.
The transversus abdominis muscle is the deepest of the 3 paired, flat abdominal muscles. It originates on the internal surfaces of the 7th–12th costal cartilages, thoracolumbar fascia, anterior three fourths of the iliac crest, and lateral third of the inguinal ligament. As with the other flat muscles, the transversus abdominis forms a broad aponeurosis that helps make up the rectus sheath before it fuses in the midline to the linea alba. Above the arcuate line, the transversus abdominis aponeurosis contributes to the posterior rectus sheath. Below the arcuate line, it is fused with the other flat muscles as the anterior rectus sheath.
For more information about the relevant anatomy, see Regions and Planes of the Abdomen.
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Anatomical depiction of the triangle of Petit from the lateral view.
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Cross-section of the abdominal wall layers. The TAP block is performed by deposition of local anesthetic between the transversus abdominis muscle and the fascial layer superficial to it.
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Illustration depicting the placement of the ultrasound probe along the abdominal wall, and the ideal placement of local anesthetic.
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Equipment needed for TAP block (ultrasound probe not shown).
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The abdominal wall layers under ultrasound. SC - subcutaneous tissue, EO - external oblique muscle, IO - internal oblique muscle, TA - transversus abdominis muscle
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Ultrasound image of abdominal layers for subcostal approach. SC (subcutaneous tissue); RA (rectus abdominis); TA (transversus abdominis); L/M (lateral and medial)
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TAP block (posterior approach) demonstrating deposition of local anesthetic between transversus abdominis muscle and its fascial plane. EO - external oblique muscle, IO - internal oblique muscle, TA - transversus abdominis muscle, P - peritoneum
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Positioning of the patient and ultrasound probe for TAP block (posterior approach).
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Ultrasound-guided TAP block (posterior approach).
