TAP Nerve Block

As recently as 2001, a novel approach to blocking the afferent nerve fibers to the abdominal wall was discovered. This technique is termed the transverse abdominal plane (TAP) block, and employed placing local anesthetic between the deepest two layers of the abdominal musculature. Analgesia would cover the entire anterior abdominal wall, making it a suitable alternative to epidural placement for any procedure that interrupts the abdomen. The transverse abdominal plane block has quite a few similarities with the ilioinguinal and iliohypogastric blocks. Indwelling catheters have also been described in current literature for a variety settings, reporting positive results.  Many of the abdominal contents are innervated by the mesenteric and celiac plexus, not the spinal afferents flowing through the transverse abdominal plane. Many patients report higher satisfaction, and 50% or higher reduction of post operative opioid requirements. It is in this sense that the TAP block demonstrates its utility. Furthermore, procedures that primarily involve disruption of the abdominal wall, such as hernia repairs, will have more complete analgesia. 

The spinal afferents that innervate the tissue and muscle of abdominal wall travel via the space between these two deepest muscle planes. The most superficial layer is the external oblique. Below this layer lies the internal oblique and transverse abdominis. These deepest two layers contain the sensory innervation to the most of the abdominal wall. Visit interactive image 38.1 to see the muscle layers of the abdominal wall.

 Like nearly all blocks, the transverse abdominal plane block was originally done by a landmark technique, taking advantage of the lumbar triangle of Petit. This triangle is comprised of three anatomical sides. The superior portion of the iliac crest borders it inferiorly. Posteriorly, it is bordered by the latissimus dorsi muscle. And anteriorly, it is bordered by the external oblique muscle. This method required the provider to place a needle above the iliac crest in the lateral plane. The traditional TAP block is performed by first identifying the lumbar triangle of Petit, and prepping the area. Generous use of local anesthetic is permitted because no nerve stimulation is required. A 20 gauge Touhy or blunt block needle is advanced until  two pops are appreciated. This represents the external oblique and internal oblique. The needle should come to rest at the junction of the transverse abdominis and internal oblique layer. After aspiration, 20 mLs of local anesthetic can be deposited. If a midline incision is planned, this must be done bilaterally to ensure proper blockade. 


Ultrasound Guided Transverse Abdominal Plane Block (TAP)

Image for the peri-umbillical TAP distribution

The first ultrasound guided TAP block was reported in 2006. Indwelling catheters have also been described in current literature for a variety settings, reporting positive results. The spinal afferents that innervate the tissue and muscle of abdominal wall travel via the two deepest planes of these layers. The most superficial layer is the external oblique. Below this layer lies the internal oblique and transverse abdominis. These deepest two layers contain the sensory innervation to the most of the abdominal wall. Many of the abdominal contents are innervated by the mesenteric and celiac plexus, not the spinal afferents flowing through the transverse abdominal plane. Many patients report higher satisfaction, and 50% or higher reduction of post operative opioid requirements. It is in this sense that the TAP block demonstrates its utility. Furthermore, procedures that primarily involve disruption of the abdominal wall, such as hernia repairs, will have more complete analgesia. It’s recently come to light, following some unfavorable articles showing poor analgesic results of TAP blocks, that the TAP block itself should be subdivided into three distinct regions and techniques. These have emerged as the sub-costal, the peri-umbilical (traditional) and the IL/IH technique. These three distinct techniques will prove helpful as the provider matches the right block  to the specific pain generator. Each distribution is illustrated graphically for your distinction in gallery 38.1. Its important to note, that with each technique, the medial probe face is pointed towards the umbilicus. 

This image shows the sono-anatomy for the peri-umbillical TAP

 Imaging for the TAP block can add safety and speed to the TAP block procedure. Rather than relying on feel to guide the depth, ultrasound imaging provides an excellent picture of the abdominal wall layers. A linear probe set to about 2-4 cm of depth can placed at any convenient location in the flank area, inferior to the ribs. If the patients body habitus, infection, or injury prevents this; any nearby relatively flat location of the abdominal flank can be substituted. This illustrates ultrasounds ability to allow the procedure to continue despite non-ideal conditions. The layers of the abdominal musculature will produce hyperechoic (bright white) lines that will traverse the screen. The probe can be placed in any reasonable orientation to obtain these images. Each layer will produce a characteristic “pop” when penetrated by a needle. Below the transverse abdominis layer, peristalsis can be seen, usually with a great deal of movement coinciding with respiration. Deep breathing by the patient can also help differentiate the bowel and peritoneal layer from the deep muscles of the abdomen. **Opinion-when viewing and identifying the layers of the abdomen, begin counting from the deepest layer. This will reduce the confusion regarding identification of the muscle layers. This can commonly occur with the fascial layers as they may present similarly to the muscle layers. A 20-22 gauge Touhy needle is recommended for this procedure. After the needle has reached the proper position, between the transverse abdominis and internal oblique, 20 milliliters of local anesthetic is deposited. The larger needle will image brighter despite the steep angle of entry. A relatively blunt tip will allow the provider to feel each muscle layer as it is penetrated by the characteristic “pop. It would seem that the blunt tip allows for fewer accidental intravascular injections for this procedure, although no research has suggested this. It is important to image the spread of local anesthetic to rule out an accidental intravascular injection. Visit gallery 38.1 to see the illustrations of the TAP anatomy, then view the TAP block including the three distinct layers of the abdominal musculature in gallery 38.2. The external and internal oblique muscle planes are the most superficial, and the transverse abdominis followed by the bowel are the deepest structures. Note the hyperechoic lines differentiating each layer. 

Image for the distribution of the sub-costal TAP

This image shows the sono-anatomy for the sub-costal TAP.

Image for the ilioinguinal/iliohypogastric TAP

This image shows safe needle position from medial to lateral for this technique.

Ultrasound guidance for the Il/IH block

Ultrasound guidance has dominated the vast majority of recent article regarding IL/IH blocks. Many articles advocate its use to reduce time of procedure, and complications and increase success rates. The procedure begins by selecting a high frequency linear probe set to 2-4 cm. Place the probe at the ASIS and observe the hyperechoic superficial surface and acoustic shadow beneath it. Position the probe’s medial border towards the umbilicus and the view, as seen in 39.1, will appear. The needle approach is from medial to lateral, in-plane. After localizing the skin and fascia with local solution, introduce a block needle or Touhy needle in-plane. Guide the needle to the junction of the internal oblique and transverse abdominis muscle layers. Aspirate and deposit 10-20 mLs of local anesthetic solution observing the spread and separation of muscle layers.


 

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