Rectus Sheath Block

Innervation of the anterolateral abdominal wall arises from the anterior rami of spinal nerves T7 to L1. Branches from the anterior rami include the intercostal nerves (T7-T11), the subcostal nerve (T12) and the iliohypogastric / ilioinguinal nerves (L1). Intercostal nerves T7 to T11 exit the intercostal spaces and run in the neurovascular plane between the internal oblique and the transversus abdominis muscles. The subcostal nerve (T12) and the ilioinguinal/ iliohypogastric nerves (L1) also travel in the plane between the transversus abdominis and internal oblique, innervating both these muscles. The T7-T12 nerves continue anteriorly from the transversus plane to pierce the rectus sheath and end as anterior cutaneous nerves. The T7-T11 nerves provide sensory innervation to the rectus muscle and overlying skin. T7 gives sensory innervation at the epigastrium, T10 at the umbilicus, and L1 at the groin.

Rectus sheath block provides somatic pain relief for abdominal wall structures superficial to the peritoneum. Its main indication outside perioperative pain relief is in management of chronic abdominal wall pain. It can be of diagnostic as well as therapeutic value in abdominal cutaneous nerve entrapment syndrome (ACNES).

Injections are generally avoided in patients with systemic infection or skin infection over puncture site, bleeding disorders or coagulopathy, allergy to local anaesthetics or any of the medications to be administered.

Rectus sheath block is done on an outpatient basis. The procedure is performed under ultrasound guidance to ensure accuracy of needle placement. Patients need to be aware that the outcome of the procedure is variable and they may not receive the desired benefits. Similarly, they must be aware of the transient nature of the therapeutic benefits and that there may need repeated injections.

Generally a mixture of local anaesthetic and steroid is injected. The local anaesthetic is probably responsible for immediate pain relief, whereas steroids are believed to be responsible for pain relief 2–6 days after their administration. For a diagnostic block, a short-acting anaesthetic alone is sufficient.

Pulsed radiofrequency treatment can be applied to the abdominal cutaneous nerves for patients who get a positive response to local anaesthetic blocks. Pulsed radiofrequency can provide sustained pain relief in patients with chronic abdominal wall pain or abdominal cutaneous nerve entrapment syndrome (ACNES).

Complications are rare, particularly if the injections are performed using a precise needle-positioning technique. Possible complications include bruising, infection, hematoma, nerve injury and reaction to the injectates. Infection can be avoided with appropriate aseptic precautions. Severe allergic reactions to local anaesthetics are uncommon. Steroid injections may produce local reactions, occurring most often immediately after injection. These local reactions last for 24 to 48 hours, and are relieved by application of ice packs. Post-procedural pain flare-up may occasionally occur, and may be treated with painkillers. Neurological complications including paraesthesias and numbness have been described but are rare.

Bowel perforation has been reported following rectus sheath block. Real time ultrasound guidance helps in minimizing this complication.