TAP Nerve Block

Transversus Abdominis Plane (TAP) Block: An Overview

Introduced as recently as 2001, the Transversus Abdominis Plane (TAP) block represents a novel regional technique for providing analgesia to the anterior abdominal wall. This block involves the deposition of local anesthetic between the internal oblique and transversus abdominis muscles—the deepest two layers of the abdominal wall musculature—targeting the afferent sensory nerves that traverse this plane.

The TAP block provides effective somatic analgesia for procedures involving abdominal wall disruption and serves as a viable alternative to epidural anesthesia, especially in postoperative pain management following lower abdominal surgeries. It shares anatomical and clinical similarities with the ilioinguinal and iliohypogastric nerve blocks and has demonstrated reduced postoperative opioid requirements, often by 50% or more, contributing to improved patient satisfaction.

Importantly, the TAP block provides somatic analgesia only. Since visceral pain fibers originate from the mesenteric and celiac plexuses, they are not addressed by this technique. As such, the TAP block is particularly beneficial for surgeries involving primary disruption of the abdominal wall (e.g., hernia repairs) rather than intraperitoneal procedures.

Ultrasound Guided Transverse Abdominal Plane Block (TAP)

Evolution and Refinement of the TAP Block

The first ultrasound-guided Transversus Abdominis Plane (TAP) block was reported in 2006, marking a significant advancement in regional anesthesia techniques for abdominal wall analgesia. Since then, indwelling catheter placementwithin the TAP plane has been described in the literature for a variety of clinical settings, with encouraging outcomesregarding postoperative pain control.

The sensory innervation of the anterolateral abdominal wall is primarily carried by spinal afferents that traverse the fascial plane between the internal oblique and transversus abdominis muscles—the two deepest muscular layers. The most superficial layer, the external oblique, lies above these. In contrast, the abdominal viscera receive innervation via the mesenteric and celiac plexuses, which are not affected by TAP blocks.

As a result, the TAP block provides somatic analgesia limited to the abdominal wall and is particularly effective for procedures involving incisions through the musculature and fascia, such as hernia repairs. Numerous studies report improved patient satisfaction and reductions in postoperative opioid requirements by 50% or more, underscoring the utility of this technique.

Evolving TAP Block Techniques

Recent literature has highlighted variability in TAP block efficacy, often due to imprecise block localization. In response, experts now recognize that the TAP block encompasses three distinct anatomical zones, each with its own technique and indications:

1. Subcostal TAP Block – Targets upper abdominal incisions

2. Periumbilical (Traditional) TAP Block – Used for mid-abdominal wall analgesia

3. Ilioinguinal/Iliohypogastric (IL/IH) TAP Block – Best suited for lower abdominal procedures

Understanding and selecting the appropriate TAP block variant based on the location of surgical pain is essential for optimal analgesic coverage. Each technique is further detailed and illustrated in Gallery 38.1 for reference.

Note: For all approaches, the medial face of the ultrasound probe should be oriented toward the umbilicus to maintain consistent anatomical orientation.

Ultrasound-Guided TAP Block: Imaging Technique and Considerations

Ultrasound guidance enhances both the safety and efficiency of the Transversus Abdominis Plane (TAP) block by providing direct visualization of the abdominal wall layers, eliminating the need to rely solely on tactile feedback. A high-frequency linear probe, typically set to a depth of 2–4 cm, should be placed on the lateral abdominal wall, just inferior to the costal margin. If standard placement is not feasible due to patient body habitus, infection, or injury, an alternative flat area on the abdominal flank may be selected. This flexibility underscores the adaptability of ultrasound in non-ideal clinical conditions.

Sonographic Landmarks and Technique

• The abdominal musculature appears as hyperechoic (bright white) linear bands.

• From superficial to deep:

  1. External oblique

  2. Internal oblique

  3. Transversus abdominis

  4. Peritoneum and bowel loops (characterized by peristalsis and respiratory movement)

A deep breath from the patient can assist in distinguishing bowel from the muscle layers.

Tip: For clarity, begin identifying layers from the deepest structure upward to avoid mistaking fascial planes for muscle layers, as their sonographic appearances may be similar.

Needle Selection and Injection Technique

A 20–22 gauge Tuohy needle is recommended for optimal visibility and control. The blunt tip offers several advantages:

• Improved tactile feedback as each muscle layer is penetrated (noted by a characteristic “pop”)

• Enhanced echogenicity, even at steep angles

• Potentially reduced risk of intravascular injection (though this remains anecdotal)

Once the needle reaches the correct fascial plane—between the internal oblique and transversus abdominis—20 mL of local anesthetic is slowly injected. Real-time visualization of anesthetic spread is critical to:

• Confirm correct plane placement

• Exclude inadvertent intravascular injection

Visual Reference

• Gallery 38.1: Illustrates general TAP anatomy

• Gallery 38.2: Shows detailed sonographic appearance of the three abdominal muscle layers

  • External and internal oblique: superficial

  • Transversus abdominis and bowel: deepest

Each layer is separated by distinguishable hyperechoic fascial lines.

Ultrasound-Guided Ilioinguinal/Iliohypogastric (IL/IH) Nerve Block

Ultrasound guidance has become the standard technique for performing ilioinguinal and iliohypogastric (IL/IH) nerve blocks, with a growing body of literature supporting its use. Numerous studies highlight ultrasound’s ability to reduce procedure time, improve block accuracy, and decrease complication rates.

Technique

1. Transducer Selection: Use a high-frequency linear probe, typically set to a depth of 2–4 cm.

2. Probe Positioning:

   • Place the probe transversely at the level of the anterior superior iliac spine (ASIS).

   • Identify the hyperechoic cortical surface of the ASIS and its underlying acoustic shadow.

   • Rotate the probe so the medial edge is directed toward the umbilicus. This orientation provides the ideal view, as illustrated in Figure 39.1.

3. Needle Insertion:

   • Insert the needle in-plane, from medial to lateral.

   • After anesthetizing the skin and subcutaneous tissue, advance a block or Tuohy needle under continuous ultrasound guidance.

4. Target and Injection:

   • Direct the needle tip to the fascial plane between the internal oblique and transversus abdominis muscles.

   • After confirming negative aspiration, inject 10–20 mL of local anesthetic, observing for appropriate spread and separation of the muscle layers.