Regional anesthesia for abdominal wall procedures can be performed using a variety of peripheral nerve blocks. These blocks are typically ultrasound (US) guided and involves injecting a local anesthetic (LA) solution into interfascial planes. US-guided transversus abdominis plane (TAP) block implicates the injection of LA in between the transversus abdominis (TA) and internal oblique (IO) muscles. The TAP block can also be targeted using anatomical landmarks at the level of the Petit triangle. This interfascial plane contains the intercostal, subcostal, iliohypogastric, and ilioinguinal nerves. These nerves give sensation to the anterior and lateral abdominal wall as well as the parietal peritoneum, providing only somatic and not visceral analgesia.
The TAP block can be for postoperative analgesia management in open and laparoscopic abdominal surgeries as well as inpatient and outpatient surgical procedures. Unilateral left or right-sided blocks are used for unilateral surgical procedures, such as cholecystectomy, appendectomy, nephrectomy, or renal transplants, while bilateral TAP blocks are used for midline and transverse abdominal incisions, such as umbilical or ventral hernia repair, cesarean deliveries, hysterectomy, and prostatectomy. TAP blocks are part of multimodal pain management for abdominal surgeries, which adds analgesic benefit to the patients, reducing postoperative opioid requirements. TAP blocks are usually placed intraoperatively, either before surgical incision or at the end of the procedure before emergence from anesthesia. The efficacy of the TAP block is dependent on the spread of LA across the interfacial plane. Newer tissue plane blocks like quadratus lumborum block provide visceral analgesia in addition to somatic analgesia.
The TAP block has become one of the most common truncal blocks performed for postoperative analgesia after abdominal surgeries. This activity reviews the anatomy of the abdominal wall, history of the TAP block, classification, approaches, techniques, and complications for this block. It also highlights the indications, contraindications, clinical significance, and equipment to perform this block in a safe manner.
Reviewing the anatomy of the anterior abdominal wall will result in a greater understanding of the neurovascular anatomy within the TAP block. The anterolateral abdominal wall has four muscles: the rectus abdominis, external oblique, internal oblique, and transversus abdominis muscles. The TAP anatomical compartment is a plane that is located between the internal oblique and transversus abdominis muscles and contains the T6–L1 thoracolumbar nerves.
The sensitive innervation of the anterolateral abdominal wall results from the spinal nerves, anterior rami. Immediately after exiting from their respective intervertebral foramina, spinal nerves divide into anterior and posterior rami. The anterior rami split into two branches, the anterior and lateral cutaneous nerves. The anterior cutaneous nerve from the T6–T11 segments gives rise to intercostal (IC) nerves, which supply sensitivity to the skin and muscles of the anterior abdominal wall. The T9–T11 IC and T12 subcostal (SC) nerves penetrate the transversus abdominis plane compartment posterior to the midaxillary line.
The lower thoracic intercostal and subcostal nerves innervate the skin of the infra-umbilical area between the midline and midclavicular lines. L1 lumbar plexus gives rise to ilioinguinal (II) and iliohypogastric (IH) nerves. II and IH provide sensory innervation to the upper hip, groin, and thigh. Branches of all these nerves variably travel between the transversus abdominis (TA) and internal oblique (IO) muscles in the TAP compartment.
The first description of the transversus abdominis plane block is accredited to Rafi in 2001, who advocated the performance of this block by anatomical landmarks at the level of the lumbar triangle of Petit. The Petit triangle edges are conformed by the iliac crest as the inferior edge, the latissimus dorsi as the posterior edge, and the external oblique as the anterior edge. The tip of the triangle is the rib cage.
Traditionally, these landmark blocks have blind endpoints (pops), making their success unpredictable. In 2006, O'Donnell introduced the term transversus abdominis plane block and modified Rafi's original description by advocating a double pop technique. In 2007, Hebbard et al. advocated the use of ultrasound guidance to identify the intermuscular planes and the use of the midaxillary line (lateral approach) instead of the triangle of Petit. In 2010 Lee et al. demonstrated that the subcostal approach covered an increased number of dermatomes (4 vs. 3 by the lateral approach) and yielded a higher sensory blockade (T8 vs. T10).
Provide analgesia after an abdominal wall procedure in a variety of abdominal surgeries are the indications of the TAP block. The TAP block can be performed for open abdominal surgeries as well as laparoscopic procedures. The TAP block is an easier and less risky substitute for epidural anesthesia in postoperative pain control for abdominal surgeries.
This procedure is contraindicated in the following scenarios:
Caution should be maintained in patients that are on therapeutic anticoagulation, pregnant and, where anatomical landmarks are difficult to distinguish (like very thin patients, elderly, or deconditioned).
The following are the necessary materials to perform a TAP block (Image 1):
The TAP block should be performed by a skilled medical provider with regional anesthesia training, such as anesthesiologists. A second healthcare provider or nurse is required to perform a pre-procedure time-out and to assist during the procedure with the ultrasound and for the injection of local anesthetic while the anesthesiologist positions the needle and directs when and how much to inject.
Before performing a TAP block, the health care provider must:
There are several TAP block techniques on how the TAP block compartment is identified:
The ultrasound-guidance technique is considered the gold standard in TAP blocks because it is easy for the operator to acquire ultrasound images and safe for the patient to perform the procedure under direct visualization of the needle before the injection of LA. For these techniques, the patient should be positioned supine for most of these approaches, except for slight lateralization for the posterior approach in some cases. A high-frequency linear or curvilinear ultrasound transducer should be used  and placed in the abdomen with gel for adequate contact and transmission of the ultrasound waves.
In the ultrasound image visualized (Image 5), the most superficial layer is skin and subcutaneous fat, then there are three muscular layers, from superficial to deep: external oblique, followed by the internal oblique, and lastly, the transversus abdominis muscle. The internal oblique muscle is usually the thickest muscle layer in the majority of patients, while the transversus abdominis muscle is the thinnest. If uncertain of the layer borders, increase the depth of the ultrasound to confirm bowel beneath the transversus abdominis muscle. Scanning posteriorly, the internal oblique and transversus abdominis muscles show the two layers come together to form the thoracolumbar fascia. Scanning medially, the aponeurosis of the three muscle layers come together to form the rectus sheath. Upon identifying the TAP compartment with the ultrasound probe, infiltrate the patient's skin using lidocaine (if the patient is awake), penetrate the skin with the block needle using an in-plane technique, making sure to visualize the needle tip on ultrasound throughout its entire trajectory. Upon entering the plane between the internal oblique and the transversus abdominis muscles, and after negative aspiration of blood, the LA is slowly injected. The TAP compartment will begin to separate, hydrodissect, or "unzip" as the LA is injected, pushing the transversus abdominis muscle down. Usually, an injection of 15 to 20 ml of LA is recommended for each side for an adult patient. The dose and volume depend on the patient's weight as well as the concentration of the LA. The spread of LA along the TAP compartment is responsible for the success of the block. Studies had shown that the efficacy of the block is improved when injecting 15 ml or more.
There are three approaches for ultrasound-guided TAP block to target the compartment anatomically:
TAP block vs. Rectus Sheath Block: The rectus sheath block targets the compartment between the rectus abdominis muscle and the posterior rectus muscle sheath. The high-frequency probe should be placed in a transverse orientation below the costal margin on the lateral edge of the rectus abdominis muscle at the upper 1/3 of the rectus muscle, where the transversus abdominis muscle extends medially and provides a layer of safety between the compartment and the peritoneum to prevent peritoneal injection of LA. In the ultrasound image should visualize the rectus muscle, the posterior rectus sheath, and the transversus abdominis muscle below the rectus sheath. The LA should separate the sheath from the muscle body, the rectus muscle should be displaced upward, and the transversus abdominis muscle downward. The LA should extend in both directions, cephalad and caudal, within the sheath. The rectus sheath block is used to provide analgesia for midline vertical or paramedian abdominal incisions such as exploratory laparotomy incision, umbilical surgeries, and for umbilical port incisions for laparoscopic surgery.
TAP block vs. Ilioinguinal and Iliohypogastric block: The ilioinguinal and iliohypogastric block targets these two nerves that are located within the TAP compartment above the inguinal ligament. The high-frequency probe should be placed cephalad and medial to the anterior superior iliac spine (ASIS) in the direction of a line between the umbilicus and the ASIS. Get the US picture of the three layers of abdominal muscles. In the TAP compartment may or may not be visible the ilioinguinal and iliohypogastric nerves as echogenic structures along with the deep circumflex iliac artery. This is a block that requires less volume of LA, approximately 5 to 10 ml. The ilioinguinal and iliohypogastric block is used to provide analgesia for inguinal hernia surgeries.
TAP block vs. Quadratus Lumborum block: The quadratus lumborum (QL) block targets the fascial plane in the posterior surface of the QL muscle. There are three types of QL blocks, and each one targets a fascial plane defined by different muscles. Compared to the TAP block, the QL block covers more dermatomes with better cephalad and posterior spread. QL blocks provide both visceral and somatic analgesia, probably due to paravertebral and epidural spread. For this block, a curvilinear probe should be located in an axial position at the level of the umbilicus and the anterior axillary line. Visualize the three layers of abdominal muscles and trace laterally until the internal oblique muscle and the transversus abdominis muscle merge, becoming the transversalis fascia (TF). The QL muscle is deep to the transversalis fascia. The fascia extends posteriorly as the thoracolumbar fascia (TLF). The needle should be inserted in-plane with the curvilinear probe at the level of the posterior axillary line in between the costal margin and the iliac crest bony prominences.
Complications related to TAP blocks are rare. Some complications have been reported in the literature, including:
It is recommended to utilize ultrasound guidance rather than anatomical landmarks to increase the success rate and minimize these complications. There have been minimal reported complications after the universal implementation of the ultrasound-guided technique for the TAP block.
Neurological injury is rare in TAP blocks, because these are field blocks, relying on the high volume of the local anesthetic injected to facilitate adequate blockade of the nerves that are located in the compartment, rather than targeting a specific nerve. If a neurologic injury occurs might be from direct nerve trauma from the needle, hematoma, or local infection. Excessive needle insertion, especially in thin, elderly, or deconditioned patients may also lead to complications such as visceral trauma, vascular injury, intraperitoneal injection, or intrahepatic injection.
Case reports have also described transient femoral nerve palsy where some of the local anesthetic injected for the TAP block could trail on the fascia iliaca below the inguinal ligament, producing an inadvertent blockage of the femoral nerve. If this incident happens, the surgical team should be made aware and the patient has to be advised regarding the potential risk for falls. LA injection within the TAP block is within an interfascial plane that is well vascularized, the reason why the operator should perform careful aspiration before injecting a local anesthetic to avoid an accidental vascular puncture and intravascular injection that might lead to local anesthetic systemic toxicity (LAST) which is a rare but known complication for the TAP block.
With the advent of US-guidance, there has been a surge in popularity for the TAP block, now beingly highly used for postoperative analgesia management following abdominal surgery. The TAP block is used as part of the multimodal analgesia management for abdominal surgeries that include the use of at least two non-opioid analgesic agents (e.g., acetaminophen, non-steroidal anti-inflammatory drug, gabapentinoids, IV lidocaine, ketamine or local anesthetic wound infiltration) in addition to oral or parental opioids.
The benefits of the TAP block includes a reduction in opioid requirements in the postoperative period and a decrease in postoperative nausea and vomiting, but no difference in visual analog pain scale scores. The TAP block has become an important addition to the clinicians because of its safety profile, ease to perform, effectiveness for pain control in a multimodal pain management approach with an increase in patient satisfaction, and in reducing the contribution to the world opioid crisis.
A multidisciplinary team approach is essential to perform regional anesthesia blocks, including the TAP block.
Following all these measurements will enhance patient care, improve the procedure outcomes, patient safety, and will enhance team performance.
The nurse is very important for the successful performance of the TAP block. Their interventions include:
The nurse should be available before, during, and after the TAP block to monitor the patient, including:
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