Ultrasound-guided transversus abdominis plane block is utilized in a variety of clinical scenarios as a diagnostic and therapeutic maneuver as well as to provide surgical anesthesia for abdominal surgeries below the umbilicus. As a diagnostic tool, ultrasound-guided transversus abdominis plane block aids in the differential diagnosis of abdominal pain helping distinguish abdominal wall pain from pain of intraperitoneal origin. This technique has great clinical utility in both children and adults when managing acute postoperative and posttrauma pain including postcesarean section pain that emanates from the abdominal wall below the umbilicus. This technique has recently been utilized to provide surgical anesthesia for laparoscopy. Pain of malignant origin involving the anterior abdominal wall has been successfully managed by the placement of a catheter for continuous infusions of local anesthetics utilizing this ultrasound-guided technique.

Exiting their respective intervertebral foramen and passing just below the transverse process are the paravertebral nerves. After exiting the intervertebral foramen, the intercostal nerve gives off a recurrent branch that loops back through the foramen to provide innervation to the spinal ligaments, meninges, and its respective vertebra and can be an important contributor to spinal pain. The paravertebral nerve also provides fibers to the sympathetic nervous system and the thoracic sympathetic chain via the myelinated preganglionic fibers of the white rami communicantes as well as the unmyelinated postganglionic fibers of the gray rami communicantes. The intercostal nerve then divides into a posterior and an anterior primary division (Fig. 96.1). The posterior division courses posteriorly and, along with its branches, provides innervation to the facet joints and the muscles and skin of the back. The larger, anterior division courses laterally to pass into the subcostal groove beneath the rib along with the intercostal vein and artery to become the respective intercostal nerves. The 12th thoracic nerve courses beneath the 12th rib and is called the subcostal nerve and is unique in that it gives off a branch to the first lumbar nerve, thus contributing to the lumbar plexus. The intercostal and subcostal nerves provide the innervation to the skin, muscles, ribs, and the parietal pleura and parietal peritoneum. The anatomic basis of the transversus abdominis plane block is the fact that the innervation of the anterolateral abdominal wall is provided by the lower six intercostal nerves and the first lumbar nerve. The anterior branches of these nerves pass within a fascial plane between the internal oblique muscle and the transversus abdominis muscle making them easily assessable for blockade with local anesthetic by placing a needle into this fascial plane (Fig. 96.2). Within this fascial plane, there are many interconnections between the various intercostal nerves, and it is thought that these interconnections form a “pseudoplexus” contributing to the efficacy of this block.

Ultrasound-guided transversus abdominis plane block can be carried out by placing the patient in the supine position with the arms resting comfortably by the patient’s side (Fig. 96.3). A total of 20 mL of local anesthetic is drawn up in a 20-mL sterile syringe. If the painful condition being treated is thought to have an inflammatory component, 40 to 80 mg of depot steroid is added to the local anesthetic. The iliac crest at the level of the midaxillary line is identified by palpation (Fig. 96.4). A curvilinear low-frequency ultrasound transducer is then placed in the transverse plane just above the iliac crest at the midaxillary line with the medial aspect of the ultrasound transducer pointed toward the patient’s umbilicus, and an ultrasound survey scan is taken (Figs. 96.5 and 96.6). The three layers of muscle, the external oblique, the internal oblique, and the transversus abdominis muscles, are identified as well with the fascial plane between the internal oblique muscle and the transversus abdominis muscle (see Fig. 96.6). When these anatomic structures are clearly identified on transverse ultrasound scan, the skin is prepped with anesthetic solution, and a 1½-inch, 22-gauge needle is advanced from the superior border of the ultrasound transducer using an in-plane approach in a medial to lateral direction with the trajectory being adjusted under real-time ultrasound guidance until the needle tip is resting within internal oblique muscle. At that point, after
careful aspiration, a small amount of solution is injected under real-time ultrasound imaging to utilize hydrodissection to reconfirm the position of the needle tip. Once the position of the needle tip is reconfirmed, the needle is carefully advanced through the deep fascia of the internal oblique muscle into the fascial plane between the internal oblique muscle and the transversus abdominis muscle. After careful aspiration, a small amount of solution is again injected to aid in identification of the exact position of the needle tip. After careful aspiration, the remainder of the solution is slowly injected under ultrasound guidance, which will demonstrate a bowing downward of the superficial fascia of the transversus abdominis muscle by the injectate (Fig. 96.7). There should be minimal resistance to injection. The needle is then removed, and a sterile pressure dressing and ice pack are placed at the injection site.