Rectus Sheath Block
The rectus sheath block was first described in 1899 and was initially used for the purpose of abdominal wall muscle relaxation during laparotomy before the adjunct of neuromuscular block.[5] Now, it is used for analgesia after umbilical or incisional hernia repairs and other midline surgical incisions.
The aim of this technique is to block the terminal branches of the 9th 10th, and 11th intercostal nerves which run in between the internal oblique and transversus abdominis muscles to penetrate the posterior wall of the rectus abdominis muscle and end in an anterior cutaneous branch supplying the skin of the umbilical area.
The most widely described approach is a blind technique, passing the needle through anterior rectus sheath and through the rectus abdominis muscle and injecting the local anaesthetic on the posterior wall of the rectus sheath.
With the patient lying supine, a point is identified 2–3 cm from midline, slightly cephalad to the umbilicus at the apex of bulge of the rectus abdominis muscle. A short-bevelled 5 cm needle, directed at right angles to the skin, is initially passed through the skin until the resistance of the anterior sheath can be felt. A definitive 'pop' should be felt as it passes through. The needle is advanced further until the firm resistance of the posterior wall is felt and injection of 15–20 ml local anaesthetic is made in 5 ml aliquots. The procedure is repeated on the opposite side of the midline.
There is a poor correlation between the depth of the posterior sheath and the age, weight, or height of patients meaning that it can be difficult to predict the depth of the rectus sheath.[5] The use of ultrasound allows non-invasive real-time imaging of the rectus sheath while the needle is placed under direct vision.
The ultrasound probe is placed in a transverse plane and positioned where there is optimum ultrasonographic visualization of the posterior rectus sheath. Either an 'in plane' or an 'out of plane' approach can be used. Local anaesthetic is injected between the rectus abdominis muscle and the posterior rectus sheath. In children, the use of lower doses of local anaesthetic has been described with ultrasound guidance compared with the landmark technique.[5]
With the posterior wall of the rectus sheath lying superficial to the peritoneal cavity, needle misplacement may lead to complications. Injection into the peritoneal cavity will lead to failure of the block and may risk bowel perforation or puncture of blood vessels, usually the inferior epigastric vessels.
In addition to incorrect placement of local anaesthetic, incomplete block may result from anatomical variance, as in up to 30% of the population, the anterior cutaneous branch of the nerves are formed before the rectus sheath and so do not penetrate the posterior wall of the rectus sheath.[2]
http://www.medscape.com/viewarticle/732996_4
