Intercostal Nerve Block

• Post thoracotomy pain
• Intercostal neuralgia
• Chronic abdominal wall pain
• Abdominal cutaneous nerve entrapment syndrome (ACNES)
• Rib fractures
• Post herpetic neuralgia (shingles)
• Costochondritis
• Post mastectomy pain

The intercostal nerves originate from 12 paired thoracic nerve roots that are intimately associated with the thoracic ribs. As the thoracic nerve roots emerge from the intervertebral foramen, they immediately split into the ventral rami that form the intercostal nerves and the posterior rami. Anterior branches form the gray and white rami communicantes of the thoracic sympathetic chain. The posterior rami innervate the zygapophyseal (facet) joints, muscles and skin of the thoracic midline and paraspinous area of the back.

The intercostal veins, arteries, and nerves (VAN) travel for the most part in the costal grove, protected from direct trauma with the nerve being most inferior on the edge of the rib. After exiting the foramen, the intercostal nerves are near the middle of the intercostal space between the parietal pleura and the inner side of the intercostal muscles. As the nerve approaches the angle of the rib, the nerve then emerges between the internal intercostal muscle layer and the outer portion of the innermost intercostal muscle to its location on the costal groove.

Small collateral nerve branches develop as the intercostal nerve progresses anteriorly, innervating the intercostal muscles and the ribs. At about the midaxillary line (MAL), the lateral cutaneous nerve arises. The lateral cutaneous nerve splits into posterior and anterior branches that innervate the skin of the chest wall from the scapular line to midclavicular line. The intercostal nerve continues anteriorly within the costal groove between the internal intercostal muscle layer and the outer portion of the innermost intercostal muscle, but as it progresses anteriorly, it once again emerges internal to the innermost intercostal muscle. As intercostal nerves approach the sternum, they emerge as the anterior cutaneous branches, innervating the anterior chest.

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.

The procedure 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.

Patients who get temporary relief from intercostal nerve block may be suitable for intercostal nerve ablation (pulsed radiofrequency treatment). This is likely to provide longer-term pain relief.

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.

Puemothorax is a known complication of intercostal nerve block. The incidence is reported to be less than 1%. Real time ultrasound guidance should help minimize this complication.