Transversus abdominis plane (TAP) blocks procedure guide

INTRODUCTION — The transversus abdominis plane (TAP) block is a fascial plane block performed by injecting local anesthetic in the plane between transversus abdominis (TA) and internal oblique (IO) muscles, or in the case of subcostal TAP block, between the TA muscle and the posterior sheath of the rectus abdominis (RA) muscles. The TAP block targets the nerves derived from the anterior rami of thoracolumbar spinal nerves (T6 to L1) as they pass through the TAP to provide analgesia for abdominal surgical procedures.

This topic will discuss the anatomy, ultrasound imaging, and injection techniques for performing ultrasound-guided TAP block variants, and complications specific to TAP blocks. General considerations common to all peripheral nerve blocks, including patient preparation and monitoring, use of aseptic technique, localization techniques, drug choices, contraindications, and complications, are discussed separately. (See "Overview of peripheral nerve blocks".)

Ultrasound for peripheral nerve blocks is discussed in detail separately. (See "Ultrasound for peripheral nerve blocks".)

ANATOMY

●Muscles and planes – The muscles of the anterolateral abdominal wall include three layers; from superficial to deep they are the external oblique (EO), internal oblique (IO), and transversus abdominis (TA) muscles (figure 1 and figure 2). These three muscles taper medially into aponeuroses that form the lineal semilunaris, which is the lateral border of the fascia of the rectus abdominis (RA) muscle. The RA muscles meet in the midline and form the linea alba.

The TA muscle extends the most medially of the three muscles, followed by the EO and then IO muscles. The TA muscle passes under the cranial portion of the RA muscle.

The TAP is the potential space between the TA and IO muscles [1]. The TAP extends from the border of the RA muscle anteromedially to the lateral margin of the quadratus lumborum (QL) muscle. The TAP is the target for midaxillary TAP blocks and laterally placed subcostal TAP blocks. Medially placed subcostal TAP blocks target the plane between the TA muscle and the posterior sheath of the RA muscle.

Scarpa's fascia forms a layer superficial to the EO, extending across the midline superficial to the RA muscle; subcutaneous fat deep to it can be confused with the EO.

●Nerves in the TAP – The anterolateral abdominal wall is innervated by the anterior rami of T6 to L1 spinal nerves. These rami become the intercostal (T6-11), subcostal (T12), ilioinguinal (L1), and hypogastric (L1) nerves (figure 3). After the thoracolumbar nerves emerge from the intervertebral foramen, they divide into anterior and posterior primary rami [2]. The anterior rami pass through the TAP [1], until they reach and perforate the RA muscle at its lateral margin, continuing as anterior cutaneous branches supplying the anterior abdominal skin (figure 2). At the midaxillary line, the anterior rami pierce the EO muscle, continuing as the lateral cutaneous branch, which further divides into anterior and posterior branches. The T12 anterior ramus passes through the QL muscle first before entering the TAP, while caudal branches emerge into the TAP at various cephalocaudal levels. The ilioinguinal and iliohypogastric nerves usually enter the TAP near the anterior third of the iliac crest, though their course varies significantly [3].

Within the TAP, segmental nerves communicate in upper and lower plexuses from which the terminal anterior cutaneous branches arise [1].

●Blood vessels in the TAP – Blood vessels that travel within the TAP include the superior and inferior epigastric vessels and the deep circumflex iliac artery (figure 4).

CLINICAL CORRELATION — TAP blocks are used for postoperative analgesia; they do not reliably provide visceral analgesia, analgesia for incisions above the umbilicus, or complete anesthesia for surgery. A single injection in the TAP may provide multisegment blockade due to the extensive network of the TAP plexuses.

Thoracoabdominal nerves enter the TAP from the costal margin in an inferolateral direction, with the T6 nerves entering lateral to the linea alba, and with subsequent nerves emerging progressively more laterally to the anterior axillary line [1]. Nerves originating from T9 to L1 enter the TAP along the anterior axillary line, just proximal to the iliac crest. Thus:

●Injection of local anesthetic (LA) in the subcostal region might provide coverage of T6 to T9.

●Injection near the iliac crest should block T9 to L1, but more reliably T10 to T12. [4-7].

Midaxillary TAP blocks provide no visceral analgesia. Lateral quadratus lumborum (QL) blocks (sometimes called posterior TAP blocks), may provide visceral analgesia. (See "Quadratus lumborum block procedure guide", section on 'Clinical anatomic correlation'.)

Unilateral TAP blocks are required for analgesia for unilateral procedures (eg, appendectomy), but for midline surgery, bilateral blocks are required [8]. For coverage of the entire anterior abdominal wall, bilateral dual (subcostal and lateral) TAP blocks are required. For coverage of the entire anterior abdominal wall including the midline, bilateral lateral TAP blocks plus bilateral rectus sheath or subcostal TAP blocks are required (figure 5).

TERMINOLOGY — Several approaches to the TAP block have been described, but these have been merged to two primary approaches that are of clinical utility: the subcostal TAP block [9] and the lateral (also called midaxillary) TAP block [10]. We agree with a 2021 consensus on nomenclature by which the posterior TAP block is described as the lateral quadratus lumborum (QL) block [11]. The anatomy and technique for the lateral QL block are described separately. (See "Quadratus lumborum block procedure guide".)

SINGLE-INJECTION TAP BLOCK — In contemporary practice TAP blocks are performed with ultrasound guidance, which we describe here. TAP blocks are usually placed under general anesthesia, either before incision or more commonly at the end of the procedure after skin closure, though they can be placed in awake patients (eg, for rescue postoperative analgesia).

Ultrasound equipment — Select a high frequency (5 to 10 MHz) ultrasound transducer, with the depth set appropriately for the patient's body habitus (3 to 6 cm).

Patient positioning — Position the patient supine.

Lateral (midaxillary) TAP block technique

●Place the transducer in an axial orientation in the midline just above the umbilicus.

●Identify the bilateral rectus abdominis (RA) muscles and the linea alba between them.

●Move the transducer laterally to the midaxillary line, visualizing the linea semilunaris, followed by the internal oblique (IO) and external oblique (EO) muscles lateral to it, and finally the EO, IO, and transversus abdominis (TA) muscles (figure 6).

Note: A high amount of abdominal subcutaneous fat in patients with obesity can make it difficult to distinguish among the three muscle layers. The IO muscle is usually the thickest layer and the TA is the thinnest [2]. To identify each muscle, we either visualize the peritoneal cavity and peritoneum first, and/or scan from anterior (medial) aponeuroses near the RA muscle to the posterior (lateral) aponeuroses near the quadratus lumborum (QL) muscle. Fat beneath Scarpa's fascia can be confused with the EO muscle. Unlike the EO muscle, Scarpa's fascia will extend medially above the RA muscle.

●With the transducer at the midaxillary line, midway between the iliac crest, insert a 20 to 22 gauge, 80 to 120 mm block needle, in plane to the transducer, in a lateral to medial (or medial to lateral) approach.

●Place the needle tip in the plane between the IO and the TA. After negative aspiration, inject 2 to 3 mL of local anesthetic (LA) or saline, visualizing separation of the IO and the TA.

●After negative aspiration, inject 20 to 30 mL of LA in 5 mL increments, with gentle aspiration between injections, visualizing spread within the TAP. (See 'Drug choice and dosing' below.)

Subcostal TAP block technique

●Place the transducer in an axial orientation below the xiphoid process (figure 6).

●Identify the bilateral RA muscles with the linea alba between them.

●Rotate the transducer and move laterally, parallel to the costal margin. Visualize the TA under or lateral to the RA muscle (figure 6 and picture 1).

●Perform a preliminary scan from medial-to-lateral to identify the anatomy, assess ultrasound visualization, and plan the needle approach and target. Identify the lateral border of the RA muscle, the TA muscle below it, and moving laterally, the EO followed by IO muscles. Visualization may be better lateral to the linea semilunaris, particularly after surgery when subcutaneous air may be present near the midline.

●Insert a 20 to 22 gauge, 80 to 120 mm block needle, in plane to the transducer, in a lateral to medial (or medial to lateral) direction (figure 7).

•For subcostal TAP medial to the linea semilunaris, place the needle tip in the plane between the posterior rectus sheath and the TA, medial to the linea semilunaris (figure 6) [12]. After negative aspiration, inject 2 to 3 mL of LA or saline, visualizing separation of the posterior rectus sheath and the TA.

•For subcostal TAP block lateral to the linea semilunaris, place the needle tip in the plane between the EO and the TA (figure 6). After negative aspiration, inject 2 to 3 mL of LA or saline, visualizing separation of the EO and TA.

●After negative aspiration, inject 20 to 30 mL of LA in 5 mL increments, with gentle aspiration between injections, visualizing spread within the TAP (figure 8). (See 'Drug choice and dosing' below.)

DRUG CHOICE AND DOSING

●Local anesthetics – Long-acting local anesthetics (LAs; eg, ropivacaine or levobupivacaine [outside the United States] 0.2 to 0.375 percent, or bupivacaine 0.25%) are used for TAP blocks. Liposomal bupivacaine is approved by the US Food and Drug Administration (FDA), though improved efficacy compared with aqueous bupivacaine has not been confirmed. (See "Clinical use of local anesthetics in anesthesia", section on 'Liposomal bupivacaine'.)

Analgesic efficacy relies on injecting an adequate volume of LA, rather than high concentration [13]. When performing multiple TAP blocks (eg, bilateral or subcostal with midaxillary), LA concentration should be reduced but volume maintained, such that 15 to 20 mL of LA is used for each injection. This has been found to be safe even when bilateral dual blocks are performed [14].

Moreover, the total LA dose injected should be within the maximum allowable dose, including the dose used for the TAP block and any other injections (eg, wound infiltration, other nerve blocks) (table 1). TAP blocks can result in LA toxicity, due to the vascularity of the TAP and the high volumes of LA used. (See 'Complications' below and "Local anesthetic systemic toxicity", section on 'Block site'.)

●Adjuvants – Adjuvant medications (eg, dexamethasone) have not been shown to extend analgesia to a clinically relevant degree when added to LA solutions for TAP block [15-19]. Epinephrine has been shown to reduce the plasma concentration of LA during TAP block and can be considered to increase the duration of block and safety of injection [20].

CONTINUOUS TAP BLOCK — TAP catheters can provide prolonged analgesia beyond the duration of single-shot techniques. In a randomized trial including 80 patients who underwent laparotomy, the addition of a continuous TAP block to a single-shot block reduced pain and morphine consumption in the first 24 hours, versus single-shot block alone [21].

●Catheter placement technique – Strict sterile technique must be used (including a sterile ultrasound transducer cover, full operating room table cover) for continuous block. The technique for continuous block is similar to a single-injection block. An 18 to 20 gauge Tuohy needle is used instead of a block needle. A single end hole or multiorifice catheter is inserted through the Tuohy needle, 3 to 6 cm into the TAP.

We inject several mL of local anesthetic (LA) through the needle under ultrasound guidance to confirm correct placement of the needle tip, visualize insertion of the catheter, and then inject the rest of the bolus through the catheter in divided doses while visualizing spread of LA. Tunneling is generally not required, though the catheter should be well secured to the skin and covered with a clear sterile dressing.

●Infusion drug dose – After injecting a bolus of LA as described above for single-injection block, we start an infusion of 0.1 to 0.2% levobupivacaine or ropivacaine, or 0.125% bupivacaine, at 5 to 10 mL/hour. If available, programmed intermittent bolus of the same solution can be used at 8 mL every hour to 15 mL every three hours.

COMPLICATIONS — Major complications of ultrasound-guided TAP blocks are rare. The most significant concern is the possibility of local anesthetic (LA) systemic toxicity due to the vascularity of the TAP, and the high volume of LA used for the block. LA systemic toxicity and techniques to avoid it are discussed in detail separately. (See "Local anesthetic systemic toxicity".)

Peritoneal puncture and organ injury are possible; risk of peritoneal puncture may be minimized with ultrasound guidance, though the incidence is unknown.

There is a reported case of transient femoral nerve palsy after ultrasound-guided TAP block for analgesia after cesarean delivery, potentially due to tracking of the LA into the plane between the transversus abdominis (TA) muscle and the transversalis fascia (figure 2) [22].

Complications common to all peripheral nerve blocks are discussed separately. (See "Overview of peripheral nerve blocks", section on 'Complications'.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Local and regional anesthesia".)

SUMMARY AND RECOMMENDATIONS

●Anatomy – The transversus abdominis plane (TAP) block is a fascial plane block that can either be performed in the subcostal or lateral (midaxillary) areas. TAP blocks are used for postoperative analgesia and do not reliably provide surgical anesthesia. (See 'Anatomy' above and 'Clinical correlation' above.)

•For a lateral (midaxillary) TAP block, local anesthetic (LA) is injected between the transversus abdominis (TA) and internal oblique (IO) muscles (figure 1 and figure 2). This block variably anesthetizes the anterior cutaneous branches of T9 to L1 (figure 3 and figure 5).

•For a subcostal TAP block, LA is injected between the TA muscle and the posterior sheath of the rectus abdominis (RA) muscle, or if performed more laterally, between the TA and external oblique (EO) muscles (figure 1 and figure 2). Subcostal TAP block anesthetizes the anterior cutaneous branches of T6-T9 (figure 3 and figure 5).

●Single-injection TAP block technique – TAP block is performed with ultrasound guidance as follows, with further explanation above. (See 'Single-injection TAP block' above.)

•Position the patient supine.

•Use a linear high frequency (5 to 10 MHz) ultrasound transducer, and a 20 to 22 gauge, 80 to 120 mm block needle.

•For lateral (midaxillary) TAP block, place the transducer in an axillary orientation, between the costal margin and the iliac crest at the midaxillary line (figure 6). Place the needle tip between the TA and IO muscles (figure 6). (See 'Lateral (midaxillary) TAP block technique' above.)

•For subcostal TAP block, place the transducer parallel to the costal margin, medial or just lateral to the linea semilunaris (figure 6). Insert the needle in plane to the transducer, placing the tip between the TA muscle and the posterior rectus sheath for medial block, and between the EO and TA for more lateral block. (See 'Subcostal TAP block technique' above.)

•For either block, after negative aspiration, inject 20 to 30 mL of LA in 5 mL increments, with gentle aspiration between injections, visualizing spread of LA (figure 8).

●Continuous TAP block technique – Continuous block is performed as described for single-injection block, using a Touhy needle with a 19 or 20 gauge catheter inserted through it and 3 to 6 cm beyond the needle tip. (See 'Continuous TAP block' above.)

●Drug choice – Long-acting local anesthetics (eg, ropivacaine or levobupivacaine [outside the United States], or bupivacaine) are used for TAP blocks. Total dose must remain within maximum allowable dose, including any other LA injections. Block efficacy depends on volume of LA rather than concentration; if necessary LA concentration should be reduced to maintain adequate volume while within recommended maximum dose of LA. (See 'Drug choice and dosing' above.)

•For single injection block – Levobupivacaine or ropivacaine 0.2 to 0.375%, or bupivacaine 0.25%

•For continuous block – Bolus injection as for single injection block, followed by continuous infusion of 0.1 to 0.2 percent levobupivacaine or ropivacaine, or 0.125% bupivacaine, at 5 to 10 mL per hour. If available, programmed intermittent bolus can be used at 8 mL every hour to 15 mL every three hours.

●Side effects and complications – Major side effects of TAP blocks are very rare. The most significant concern is for LA systemic toxicity due to the vascularity of the TAP and high volume of LA used for the block. (See 'Complications' above.)