Transversus abdominis plane (TAP) block

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By Drs Peter Hebbard and Michael Fredrickson


The transversus abdominis plane (TAP) block can block the lower six thoracic and first lumbar spinal nerves via a single injection immediately cephalad of the iliac crest and slightly posterior to the level of the mid axillary line. 1, 2 The transversus abdominis plane (TAP) block is therefore useful for most surgical procedures involving incisions of the mid and lower abdominal wall. 13 

The transversus abdominis plane (TAP) block has been mainly described in adults but reports in children are increasing and it will undoubtedly develop a place in the pediatric population for lower abdominal procedures such as colostomy formation and open appendicectomy. Published reports in children include a case report in a 9-year old for analgesia after open appendicectomy; 4 a small series by this author involving children undergoing inguinal procedures, 5 and neonates having a range of abdominal procedures. 6 For inguinal procedures, recent studies have shown that a classic ilioinguinal/iliohypogastric block (at the level of the anterior superior iliac spine) provides better intra and postoperative analgesia than a classic transversus abdominis plane (TAP) block (at the level of the mid axillary line). 7


Anatomy

The spinal afferent nerves supplying the abdominal wall travel between the transversus abdominis and internal oblique muscles of the abdominal wall in a potential space termed the transversus abdominis plane ('TAP'). The nerves continue anteriorly to reach the rectus sheath which surrounds the rectus abdominis muscles.  In the TAP posterior to the mid-axillary line, the spinal afferent nerves have not yet pierced the muscular abdominal wall. This position therefore represents a logical and readily accessible compartment for the placement and subsequent cephalad spread of local anesthetic ("Posterior" TAP block).

The L1 derived nerves (ilioinguinal and iliohypogastric) have a different course to the thoracic nerves in that they generally remain deep to the transversus abdominis muscle until the level of the anterior one third of the iliac crest (line from the ASIS to posterior superior iliac spine). The ilioinguinal nerve may also pass over the iliac crest onto the iliacus muscle before re-entering the muscular abdominal wall. In the inguinal area, the external oblique muscle and its aponeurosis is innervated by the lateral branches of the subcostal and iliohypogastric nerves. The medial part of the groin is supplied by the genitofemoral nerve. The genitofemoral nerve descends on the external iliac artery until penetrating the inguinal ligament around the deep inguinal ring (Fig. 1). The clinical relevance of these anatomical variations is that for optimal anesthesia/analgesia of the inguinal area, a TAP block should be performed at the level of the anterior one third of the iliac crest (Fig. 2), and be supplemented to cover the subcostal/iliohypogastric nerve lateral branch innervation, and for inguinal hernia surgery, the area innervated by the genitofemoral nerve. The lateral branch innervation can be covered by separate infiltration of the external oblique muscle intramuscular branches lateral to the iliac crest. The genitofemoral nerve innervation can be blocked by infiltration around the pubic tubercle, or by direct LA placement under the inguinal ligament in the fascial sheath of the femoral artery. LA here will pass cephalad along the vessel to block the nerve. This can be performed using an in-plane approach with the artery in long axis. 

 


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 Fig. 1. Section of the inguinal area along the direction of the incision for open inguinal hernia repair (ASIS to symphysis). Green shows the innervation of the iliohypogastric nerve anterior branch; purple the iliohypogastric nerve lateral branch, and blue the genitofemoral nerve. EO=external oblique, IO=internal oblique, TA=transversus abdominis.




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 Fig. 2. Transversus abdominis plane (TAP) block: needle and probe position for the "Anterior" TAP block (to include the L1 nerves).

 


Skill level: Simple.


Procedure time: 1-3 mins (1 min for experienced practitioners)


Common indications

Postoperative analgesia for: 

1. Infraumbilical midline incision laparotomy 

2. Laparoscopic procedures 

3. Iliac crest bone graft harvesting 

4. Pfannenstiel incision e.g. caeserian section, abdominal hysterectomy, ureteric reimplantation (ilioinguinal block is probably more effective for these incisions)


Sedation: e.g. midazolam 2 mg + alfentanil 250-500 mcg or more commonly after GA.


Surface landmarks: mark out the side to be blocked.


Needle: e.g. 8-10 cm 18G Tuohy needle.


Setup

1. High frequency linear array probe e.g. SonoSite L38 

2. 8-10 cm 18G Tuohy needle. 

3. 20 mL LA filled syringe


Procedure for "Posterior" TAP Block

1. Place the probe on the anterior abdominal wall in the transverse plane where the three muscle layers are most distinct on ultrasound, which is approx. anterior to the mid axillary line (Fig. 2). 

2. Slide the probe laterally/posteriorly to the posterior limit of the three muscles (Fig. 3).


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 Fig. 3. Transversus abdominis plane (TAP) block: sonogram indicating the target point for the "Posterior" TAP block (for lower abdominal incisions). EO=external oblique muscle. IO=internal oblique muscle. TA=transversus abdominis muscle. SUP=superior. INF=inferior.


3. The skin puncture point is selected to give a needle depth such that with an anterior-to-posterior needle direction, the needle is aligned approx. perpendicular to the ultrasound beam.

4. Following skin puncture, the probe is slid anteriorly on the lateral abdominal wall to image the needle. The probe then follows the needle in-plane posteriorly as it is advanced towards the posterior limit of the TAP. 

5. Once the needle tip is visualised in or near the TAP, a mL or two of LA is injected with the aim of observing separation of the transversus abdominus and internal oblique muscles. If the LA appears to be spreading within the internal oblique muscle, attempt short, sharp needle advancements to penetrate the fascia between internal oblique and transversus abdominis. If LA spread appears to be within the transversus abdominis muscle, withdraw the needle slightly while continuously injecting LA until muscular separation occurs. When satisfactory separation is observed, the full LA dose is injected while simultaneously observing appropriate spread within the plane.

6. For "Anterior" TAP block, the target needle endpoint is more anterior to the posterior limit of the 3 muscles (Fig. 4).



TAP block US image

Fig. 4. "Anterior" TAP block sonography (pediatric subject). EO=external oblique muscle. IO=internal oblique muscle. TA=transversus abdominis muscle. Blue line points towards needle shaft (tip is within the TAP)



Local anesthetic regimen: 15-20 mL ropivacaine 0.25-75% each side (paediatric dose: 0.3-0.4 mL/kg) 8, 9


Specific Complications

1. Liver (or other viscera) trauma/laceration. Exceedingly unlikely if the needle tip is maintained superficial to the transversus abdominis muscle. Risk is increased in obese patients due to the difficulty often encountered with needle tip visualisation.


Clinical PEARLS

1. The ultrasound guided approach to the transversus abdominis plane (TAP) block may be performed bilaterally with the operator standing on the same side of the patient.

2. Having the needle orientated more perpendicular to the orientation of the fascia, and the bevel itself facing the fascia facilitates fascial penetration, which usually requires short sharp needle advancements. In general, the closer the needle-skin puncture site is to the probe, the more parallel the needle shaft will be to the direction of teh US beam. This makes shaft visualisation more difficult, but facilitates fascial penetration. Conversely, the further away the needle-skin puncture site is from the probe, the more perpendicular the needle shaft will be to the US beam. This makes shaft visualisation easier, but fascial penetration more difficult.

 

 

Videos

Video 1. "Anterior" transversus abdominis plane (TAP) block.



Video 2. "Anterior" TAP block sonography (pediatric). Images are similar for adults albeit involving higher depths. Note the "bubble" LA pattern indicating separation of the internal oblique and transversus abdominis muscles.



Video 3. "Anterior" TAP block sonography (adult). Initial scanning is on the anterior abdominal wall followed by probe movement posteriorly.


References


1.         McDonnell JG, O'Donnell B, Curley G, et al. The analgesic efficacy of transversus abdominis plane block after abdominal surgery: a prospective randomized controlled trial. Anesth Analg 2007;104:193-7.

2.         McDonnell JG, O'Donnell BD, Farrell T, et al. Transversus abdominis plane block: a cadaveric and radiological evaluation. Reg Anesth Pain Med 2007;32:399-404.

3.         Hebbard P, Fujiwara Y, Shibata Y, et al. Ultrasound-guided transversus abdominis plane (TAP) block. Anaesth Intensive Care 2007;35:616-7.

4.         Laghari ZA, Harmon D. Ultrasound-guided transabdominus plane block. J Clin Anesth 2008;20:156-8.

5.         Fredrickson M, Seal P, Houghton J. Early experience with the transversus abdominis plane block in children. Paediatr Anaesth 2008;18:891-2.

6.         Fredrickson MJ, Seal P. Ultrasound-guided transversus abdominis plane block for neonatal abdominal surgery. Anaesth Intensive Care 2009;37:469-72.

7.         Fredrickson MJ, Paine C, Hamill J. Improved analgesia with the ilioinguinal block compared to the transversus abdominis plane block after pediatric inguinal surgery: a prospective randomized trial. Paediatr Anaesth 2010;20:1022-7.

8.         Willschke H, Bosenberg A, Marhofer P, et al. Ultrasonographic-guided ilioinguinal/iliohypogastric nerve block in pediatric anesthesia: what is the optimal volume? Anesth Analg 2006;102:1680-4.

9.         Willschke H, Marhofer P, Bosenberg A, et al. Ultrasonography for ilioinguinal/iliohypogastric nerve blocks in children. Br J Anaesth 2005;95:226-30.