Abdominal wall blocks: Difference between revisions

Regional anaesthesia is an essential component of paediatric anaesthetic practice. Regional blocks allow for a lighter plane of anaesthesia during surgery, and provide excellent pain control after surgery.1 The aim of this review is to describe how to perform the three most common abdominal wall blocks in children: ilioinguinal/ iliohypogastric, rectus sheath and transversus abdominis plane. We will describe landmark techniques as well as ultrasound-guided techniques. Ultrasound guided blocks are increasingly considered the gold standard as it is possible to identify the anatomy more accurately, which increases the reliability of the block and allows a smaller dose of local anaesthetic to be used. Regional anaesthetic blocks are simple to do, but should be taught by an appropriately skilled mentor. All local anaesthetic blocks should be performed using an aseptic technique; clean the skin with an alcohol-based cleaning solution and wear gloves. Ideally use a short-bevelled block needle for abdominal wall blocks, but a 23G or 21G hypodermic needle may also be used; many advocate ‘blunting’ the tip of the needle on the inside of the cap of the needle to better appreciate the facial planes. All the blocks described should be performed after induction of general anaesthesia.  

The ilioinguinal/iliohypogastric nerve block (ILNB) provides excellent analgesia after inguinal hernia repair, hydrocele repair and orchidopexy. It does not abolish visceral pain due to peritoneal traction or manipulation of the spermatic cord during inguinal hernia repair or orchidopexy. Bilateral blocks can be used, but it is important to keep the dose of local anaesthetic within safe limits. Perform ILNBs after induction of anaesthesia, before the start of surgery; it is important to make sure that the child is adequately anaesthetised when the cord structures are mobilised, and that additional local infiltration/analgesia is used if a scrotal incision is made. There is much anatomical variation of nerve position between the abdominal wall muscles. The effectiveness of this block can be improved greatly when performed with ultrasound, and lower amounts of local anaesthetic can be used.2 Anatomy (see Figure 1):  

* In infants the average nerve-peritoneum distance is only 3.3mm3 .  

Use a volume of up to 0.5ml.kg-1 0.25% bupivacaine for the landmark technique. In expert hands as little as 0.075 ml.kg-1 0.25% bupivacaine can be effective using ultrasoundguidance; 4 we recommend 0.1-0.2ml.kg-1.  

Place the patient supine. Clean the skin over the lower quadrant of the abdominal wall, including the skin over the anterior superior iliac spine (ASIS). Draw up the appropriate dose of local anaesthetic. The needle insertion point is close to the ASIS, approximately 2 - 5mm medial to the ASIS on a line drawn between the ASIS and the umbilicus.5 Some suggest using the child’s finger as an appropriate guide for the distance from the ASIS to the injection point (NOT the operator’s finger! - see Figure 2). It is important to keep the injection point high, away from the skin crease in the groin where the surgeon will make the incision; otherwise the operating field will be obscured.

The ASIS is the most easily recognizable landmark for this block, it appears as a dark echo-lucent shadow beneath a hyperechoic peak and should be kept at the lateral part of the screen for orientation. Identify (always from the inside out) the peritoneum (hyperechoic line, underneath it you may see peristalsis), transversus abdominis muscle, and internal oblique muscle. The external oblique muscle may not be visible as a distinct muscle layer at this level as it may have become an aponeurosis. Slide the probe up over the iliac crest, whilst maintaining the same orientation of the probe, to bring all three muscles into view as three distinct layers. This may be useful if there is any doubt about the anatomy and the relevant planes. The ilioinguinal and iliohypogastric nerves are seen in close proximity to each another as two small round hypoechoic structures with a hyperechoic border. They lie in the plane between the internal oblique muscle and the transversus abdominis muscle close to the ASIS. In children the average distance from the ilioinguinal nerve to the ASIS is 7mm.4

A rectus sheath block provides intraoperative and postoperative analgesia for mid-line abdominal incisions, for instance, periumbilical surgery (e.g. umbilical hernia repair,6 paraumbilical hernia repair, epigastric hernia repair), pyloromyotomy, laparoscopic surgery and excision of urachal remnants.

Introduce a short-bevelled needle perpendicularly through the skin Advance the needle medially at an angle of 60° towards the umbilicus. Identify the anterior sheath by moving the needle back and forth until a scratching sensation is felt; a pop is felt as the needle passes through the anterior sheath. Advance the needle through the muscle with continued movement of the needle until a scratching is again felt (this indicates the posterior sheath). If there is resistance to injection, it is not sited correctly. Repeat the technique for the opposite side. In children under 10 years of age the rectus muscle is rarely greater than 1cm in thick, therefore when performing this technique the needle should not be inserted any further than this. The depth of the posterior rectus sheath in children is unpredictable, and many advocate using ultrasound for this reason.7

The standard transversus abdominis plane (TAP) block provides intraoperative and postoperative analgesia for lower abdominal incisions. A subcostal TAP block can be provide analgesia for abdominal surgery above the umbilicus. TAP block can be performed unilaterally (e.g. inguinal hernia repair), or bilaterally (e.g. for laparoscopic surgery). It may be used as an alternative to an epidural, but it does not provide visceral analgesia; it should be performed after induction of anaesthesia, and adequate anaesthesia should be provided during visceral manipulation. A comprehensive review of the transversus abdominis plane (TAP) block can be found in WFSA ATOTW 239.8

Peritoneal perforation, organ perforation (in neonates the liver and spleen are particularly prominent). The TAP block has a higher rate of complications than other blocks in children.9