Once performed using only landmarks and tactile sensation, the transversus abdominis plane (TAP) block has evolved to be one of the most commonly performed field blocks under ultrasound guidance.
Common indications for TAP blocks include major abdominal surgeries such as colorectal, cesarean sections, gynecologic, urologic, and laparoscopic abdominal surgeries. Hernia repairs and other procedures involving the abdominal wall can also benefit from TAP blocks. The TAP block covers somatic incision pain, but not visceral pain. TAP blocks are often an alternative for patients on anticoagulation or when neuraxial analgesia is contraindicated.
Absolute contraindications for TAP blocks include patient refusal, allergy to local anesthetics, and infection over the site of injection. Relative contraindications include patients with poor landmarks; this can be potentially avoided by performing the block preoperatively before surgical changes and inflammation ensue.
The anterior abdominal wall is innervated by the anterior rami of T6-L1 (Figure 80-1). The terminal branches of these nerves course through the abdominal wall between the internal oblique and transversus abdominis muscle; this intermuscular plane is known as the TAP (Figure 80-2). The rami of T6-L1 enter the TAP more laterally as they go down. For example, T6 enters the TAP just lateral to midline at the linea alba, whereas L1 enters the TAP lateral to the anterior axillary line. Clinically, this may explain why providers see higher success rates and improved analgesia for lower abdominal surgeries. Injection of local anesthetic within the TAP can provide unilateral analgesia to the skin, muscle, and parietal peritoneum of the anterior abdominal wall.
Figure showing the innervation of the trunk and the abdominal wall. (Reproduced with permission from Karmakar MK, Soh E, Chee V, Sheah K. Atlas of Sonoanatomy for Regional Anesthesia and Pain Medicine. New York: McGraw Hill; 2018.)
Figure showing the arrangement of the muscles of the anterior abdominal wall (external oblique, internal oblique, transversus abdominis, and rectus abdominis) with their aponeurosis, including the rectus sheath. (Reproduced with permission from Karmakar MK, Soh E, Chee V, Sheah K. Atlas of Sonoanatomy for Regional Anesthesia and Pain Medicine. New York: McGraw Hill; 2018.)
For the TAP block, patients are placed in the supine position. At the midaxillary line, the costal margin and the iliac crest are palpated. The ultrasound transducer is placed laterally above the iliac crest scanning medially until distinct muscle layers are noted (Figure 80-3). This technique provides analgesia below the umbilicus along the abdominal wall (T10-L1). Subcostal TAP blocks can be performed for analgesia above the umbilicus up to T6. From superficial to deep, one ...