Truncal Block - Technique and Complications

Introduction:

Regional anesthetic techniques are only part of a successful multimodal pain management plan. The application of peripheral and paraneuraxial blocks to deliver chest wall and abdominal analgesia has become more prevalent in recent years. As hospitals strive to reduce the length of stay and enhance the patient experience, pain management will play a key role in achieving these objectives. With the advent of portable ultrasound machines in the operating rooms, the regional anesthesia practice has shifted from landmark-based methods to regional blocks delivered under direct vision using the ultrasound machine. Until Hebbard et al. described the ultrasound-guided transversus abdominis plane (TAP) block, the application of ultrasound in regional anesthesia was confined to peripheral nerve blocks. The following years saw novel regional anesthesia techniques advancing on the trunk, hence truncal blocks.

The ultrasound-guided truncal blocks are distinguished because, unlike peripheral nerve blocks, no nerve or plexus must be identified: Local anesthesia (LA) is administered into a specific muscle plane, which diffuses and reaches the desired nerves. This simple mechanism has made nerve block administration simple and versatile.

What Is the Blood Supply of the Abdominal Wall?

• The anterior rami of the thoracolumbar nerves (T6 to L1) supply the abdominal wall (skin and muscles) and the parietal peritoneum.

• The nerves travel in a neurovascular sheath beneath a fascial layer that persists between the internal oblique (IO) and transversus abdominis (TA) muscles in the anterolateral abdominal wall.

• There is considerable branching and communication between T9 to L1 nerves within this plane, with the more significant part of interactions taking place at the 'transversus abdominis plane (TAP) plexus,' frequently found adjoining the deep circumflex iliac artery (DCIA).

• The rectus sheath plexus is formed by nerves that run along the posterior aspect of the rectus abdominis (RA) muscle in the anteromedial abdominal wall. This rectus sheath plexus is generally observed near the lateral branch of the deep inferior epigastric artery (DIEA).

• Successive research has revealed that blocking all three plexuses can result in abdominal wall anesthesia spanning the sixth thoracic to the twelfth thoracic dermatomes.

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• When the local anesthetic is injected along the costal margin, it reaches the intercostal plexus and the rectus sheath plexus. In contrast, injection at the TAP only anesthetizes the TAP plexus.

• Should state that blocking these plexuses would not contribute to anesthesia of the visceral peritoneum, which is innervated by the autonomic nervous system.

• Visceral analgesia requires sympathetic blockade mainly through neuraxial or paravertebral approaches.

What Is the Landmark Technique for Tap Block?

• The anterior branches of the intercostal nerves, the seventh thoracic to the twelfth thoracic, which supplies the anterior abdominal wall, as well as the first lumbar spinal nerve (L1) anterior rami, travel in the plane between the internal oblique muscle (IOM) and the transversus abdominis muscle (TAM).

• The approach aims to inject 15 to 20 mL of LA into the plane between these muscles. Dr. Rafi introduced the landmark-based approach.

• Used a blunt-tipped needle to access perpendicularly at the Petit lumbar triangle and obtain two pops or loss of resistance (LOR). For midline surgical interventions, the block must be performed on both sides. The TAP block is the simplest and most widely used truncal block.

• TAP block is approached in three ways:

  • Approach From the Posterior Aspect: Petit's lumbar triangle was injected, usually used in the landmark-based technique.

  • Approach From the Lateral Aspect: LA is deposited in the neurovascular plane between the internal oblique muscle (IOM) and transversus abdominis muscle (TAM) using an ultrasound transducer (UST) positioned transversely in the anterior axillary line, just above the iliac crest.

  • Approach From the Oblique Subcostal: LA is administered between the TAM in the subcostal region and the posterior rectus sheath (PRS).

  • Oblique subcostal TAP (OSTAP) is also known as upper TAP block. The word dual TAP refers to the infusion of TAP block in both the lower (that is, lateral approach) and upper zones.

  • Offering total analgesia to the anterior abdominal wall, a dual TAP block must be administered bilaterally. This technique is also referred to as the four-quadrant TAP block.

What Is the Ultrasound Guided Technique for TAP Block?

• The ultrasound-guided TAP block is an introductory-level technique block. The patient is lying horizontally with the face and torso facing up, but in the case of an obese patient positioned on side‐lying with pillows placed along the patient's back may be beneficial.

• A linear UST with a frequency of 10 to 18 MHz and a depth setting of 3 to 5 cm (based on the amount of fat tissue) is positioned transversely across the abdomen at the anterior axillary line above the iliac crest.

• External oblique muscle (EOM), internal oblique muscle (IOM), and transversus abdominis muscle (TAM) (superficial to deeper) can all be easily spotted beneath the adipose tissue, with IOM being the most apparent of the three.

• The peritoneal cavity is located deep within the TAM and is distinguished by the movement of the bowel loops. If assessing all three layers is complicated, the UST should be positioned at the midline, and the rectus abdominis muscle (RAM) be recognized.

• The UST is shifted laterally where the RAM tapering takes place, terminates in the linea semilunaris, and the obliques start. The needle is then introduced after the UST has been shifted laterally to a spot where the three muscles can be differentiated.

• A 100 mm Tuohy needle of 20 gauge or 22 gauge is chosen and inserted from anterior to posterior. The goal is to administer 15 to 20 mL of LA between the IOM and TAM. In addition, injecting a small amount of fluid (one to two mL saline or LA) to hydro-dissect, the proper plane may help with precise needle tip position.

• After the injection, the spindle-shaped hypo-echoic fluid pocket in the space lined by the hyper-echoic fascia of the IOM and the TAM confirms proper injectate placement.

What Are the Complications of TAP Block?

The TAP block and its variations are simple to perform, with few risks:

• TAP block's most severe side effect is improper needle progression through the peritoneum, which causes injuries to the organs underneath, such as a lacerated liver or bowel perforation.

• Even before the placement of the block, a risk-benefit analysis is always performed, as the risk may outweigh the advantage in patients with poor anatomy recognition.

• Patients who have had earlier abdominal surgeries with usual abdominal musculature distortion, air entrapment in the tissues, or extreme body habitus after laparoscopic surgery.

What Are the Contraindications for TAP Block?

• Patient refusal or localized infection in the area.Injection to the intraperitoneal region, liver trauma, and catheter breakage; it is assumed that the application of ultrasound has made these blocks safe and secure.

Conclusion:

Perioperative pain control will become crucial in the future. Regional anesthetic procedures are only one aspect of a successful multimodal pain control plan. Truncal blocks may provide comparable analgesia when used with other regional anesthetic methods. Although there is a statistically significant decrease in morphine consumption with TAP block, the therapeutic efficacy of the reduction in opiate intake for the surgical population remains unclear.