BLOCK AT A GLANCE
Fascial plane injections of the local anesthetic (LA) between the transversus abdominis and internal oblique muscles.
Indications: Analgesia for the abdominal wall and the parietal peritoneum
Goal: Spread of an LA in the plane to block the lateral and anterior branches of the spinal nerves T6-L1
Local anesthetic volume: 10 to 20 mL per site, depending on the required block extension and the maximum recommended dose
The ultrasound (US)-guided transversus abdominis plane (TAP) block is a commonly used analgesic technique for surgeries involving the abdominal wall, as part of a multimodal postoperative pain treatment. Analgesia with a TAP block is limited to the somatic component and highly dependent on the extent of interfascial spread. Several approaches along the fascial plane have been described to block specific areas of the abdominal wall. The efficacy of a TAP block has been documented in a variety of indications, such as cesarean delivery, hysterectomy, cholecystectomy, colectomy, prostatectomy, and hernia repair.
Similar to other fascial plane infiltrations, the duration, extent, and quality of the analgesia show considerable variability, which depends on the amount of LA that effectively reaches the targeted nerves.
Analgesic effects of the US-guided TAP block can be explained by the organization of the thoracolumbar nerves along the musculofascial anatomy of the anterolateral abdominal wall. There are four paired muscles in the anterolateral abdominal wall: the rectus abdominis (superficial, parallel in the midline), the external oblique, internal oblique, and transversus abdominis muscles (deep and most lateral). The myofascial plane of interest for the TAP block is located between the transversus abdominis and the internal oblique muscles.
The abdominal wall is innervated by the thoracoabdominal nerves (T6-T12) and the ilioinguinal/iliohypogastric nerves (L1). After emerging from the paravertebral space, the ventral rami of the intercostal nerves travel into the TAP plane between the transversus abdominis and the internal oblique muscles. At the level of the midaxillary line, the ventral rami give out the perforating lateral cutaneous branches, which innervate the lateral abdominal wall. Segmental nerves from T6-T9 enter the TAP medial to the anterior axillary line, while the other nerves enter progressively more laterally. Intercostal nerves eventually enter the sheath of the rectus abdominis muscle at its lateral margin (linea semilunaris). Here, the intercostal nerves give out the perforating anterior cutaneous branches that provide innervation of the anteromedial abdominal wall (Figure 38-1). The transversalis fascia covers the internal surface of the transversus abdominis muscle and aponeurosis, separating them from the underlying preperitoneal fat and peritoneum.
Anatomy and innervation of the abdominal wall.
CROSS-SECTIONAL ANATOMY AND ULTRASOUND VIEW
The disposition and interrelation of the muscular layers of the abdominal wall vary depending ...