Analgesia for midline abdominal surgery.
The anterior rami of T6-L1 nerve roots supply sensation to the anterior abdominal wall. The intercostal nerves exit the intercostal space and run in the fascial plane between the internal oblique and transversus abdominis muscles. The anterior divisions run anteriorly to pierce the posterior rectus sheath. They then traverse the rectus abdominis muscle to pierce the anterior rectus sheath and supply sensation to the anterior abdominal wall.
Midline of the abdomen, linea alba, rectus abdominis muscles.
Supine with arms by the side to allow access to the anterior abdominal wall. Place the transducer transversely across the abdomen above the level of the umbilicus.
Figure 1: Patient, transducer and needle positioning for a) lateral to medial in-plane rectus sheath block and b) cephalad to caudal in-plane rectus sheath block, just superior to the umbilicus.
Start with the transducer in the midline and identify the linea alba and rectus muscle on either side. The rectus sheath is the hyperechoic fascial plane encircling the rectus abdominis muscle. The transversalis fascia lies deep to the rectus sheath, leading to the ‘double hyperechoic line’ deep to the rectus abdominis muscle on ultrasound. The transversalis fascia encircles the whole peritoneal cavity. The peritoneum lies immediately deep to the transversalis fascia. Superior to the umbilicus care must be taken to identify and avoid the superior epigastric artery, which can lie deep to or within the rectus sheath. Doppler can be used to aid visualisation. Figure 2: a) ultrasound image showing the left rectus abdominis muscle b) annotated image (Rectus=rectus abdominis muscle; LA=linea alba; PRS=posterior rectus sheath; TF=transversalis fascia. The yellow line, superficial to the PRS, highlights the desired plane for local infiltration).
Hyperechoic fascial line deep to the rectus abdominis muscle.
Using an in-plane technique from either lateral to medial or cephalad to caudal, the needle is passed through the rectus abdominal muscle. The aim is to ll the plane between the rectus abdominis muscle and the posterior rectus sheath. If in the correct plane then local anaesthetic can be seen neatly peeling the rectus muscle off the posterior rectus sheath (Figure 3).
Figure 3: Ultrasound images of the anterior abdominal wall a) before rectus sheath block and b) after injection of local anaesthetic for rectus sheath block. (Large white arrow indicating transversalis fascia; Large yellow arrow indicating posterior rectus sheath; LA=local anaesthetic; small white arrows highlighting the needle passing through the rectus abdominis muscle).
1. Because innervation of the midline is from both sides bilateral rectus sheath blocks must be performed in all cases.
2. Besides the nerves, there are also vessels present in the posterior rectus space; the posterior intercostal and superior and inferior epigastric vessels. Doppler may help identify these vessels, which if seen, should be avoided during needle insertion.
3. For midline incisions the rectus sheath block can be inserted before knife to skin. If the incision will be paramedian (i.e. cutting through the rectus muscle) then the block can be performed post-operatively.
4. The tendinous intersections seen on the anterior aspect of the rectus abdominis muscle (six pack) are not present in the posterior part of the muscle. This allows free ow of local anaesthetic up and down the length of the abdominal wall.
5. Rectus sheath catheters are very popular for post-operative analgesia when used as part of an enhanced recovery after surgery technique (ERAS) for lower midline laparotomies.
6. For rectus sheath catheter insertion we recommend to orientate the long-axis of the transducer in a cephalo-caudal direction (Figure 1b). This may encourage the catheter to lie along the length of the abdominal wall and improve proximal-distal spread.
Text and images have been reproduced from the 2nd edition of the RA-UK Handbook, which can be purchased on Amazon, or is received on joining RA-UK. This excellent resource also contains practical descriptions of all of the advanced blocks referenced in the editorial.