Anatomy of Intercostal Nerves

The twelve pairs of thoracic spinal nerves (T1-12) are divided into ventral and dorsal rami after they pass through the intervertebral foramina. The ventral rami of T1-T11 form the intercostal nerves that enter the intercostal spaces. The ventral ramus of T12 forms the subcostal nerve that is located inferior to the 12th rib. The dorsal rami of T1-T12 pass posteriorly to supply sensation to skin, muscles, and bones of the back.¹

Intercostal nerves are composed of dorsal horn sensory afferent fibers, ventral horn motor efferent fibers, and postganglionic sympathetic nerves. The major branches of intercostal nerves are anterior and lateral cutaneous branches (Fig. 31-1). These branches divide and innervate the skin and intercostal muscles of an individual segment along with variable collateral innervation of the adjacent segments. Because of such collateral innervation, it is necessary to block a level above and below the desired level when an intercostal nerve block is performed.

Figure 31-1 Anatomy of an intercostal nerve.

(Adapted from Ferrante FM, VadeBoncouer TR: Postoperative Pain Management. New York, Churchill Livingstone, 1993. Elsevier.)

Throughout its course, each intercostal nerve is associated with an artery and a vein. The intercostal arteries are derived directly from the aorta. The intercostal veins are derived from the confluence of venules along the chest and end in the azygous and hemiazygous veins. The intercostal nerve travels inferior to the vein and artery of the same segment (Fig. 31-2).

Figure 31-2 Intercostal nerve block: Cross-sectional anatomy.

(From Brown DL: Atlas of Regional Anesthesia, 3rd ed. Philadelphia, Saunders 2006, p 240.).

Pathophysiology of Intercostal Neuralgia

The pathogenesis of acute intercostal neuralgia involves multiple etiologies, such as skin and muscle injury, costochondral dislocation, costovertebral ligament damage, postherpetic neuralgia, postthoracotomy pain, or intercostal neuritis. The pathophysiology of acute pain involves chemosensitive ion channels in peripheral nociceptors that are activated by cytokines released from damaged tissue or inflammatory cells. Activation of these channels results in generation of action potentials that are conducted from the peripheral nociceptors in the chest area to the thoracic spinal cord via intercostal nerves.

The pathophysiology of chronic intercostal neuralgia pain is complex and involves a combination of peripheral, central, and psychological mechanisms. In some patients, a structural or inflammatory source can be identified; however, most patients encountered in clinical practice have primary pain disorders in which the etiologies are uncertain.

Indications for Intercostal Nerve Blocks

An intercostal nerve block is used for therapeutic and diagnostic purposes. Intercostal nerve blocks manage acute and chronic pain in the chest area. Common indications for an intercostal nerve block are described subsequently.

Chest wall surgery: An intercostal block with a single injection or an indwelling catheter offers analgesia for thoracotomy and percutaneous drainage tubes. It also helps relieve pain after upper abdominal or flank surgery.

Chest wall trauma: Single injections around the appropriate intercostal nerves or continuous infusion with intercostal catheters helps to control pain resulting from fractured ribs and other chest wall trauma.

Shingles or postherpetic neuralgia: An intercostal nerve block(s) is used to treat pain caused by shingles—an acute via herpes-zoster infection resulting in inflammation of the intercostal nerves and dorsal root ganglion.

Chronic conditions: An intercostal nerve block is helpful in the management of pain associated with chest wall tumors, nerve entrapment syndromes, thoracic spine pain, and intercostal neuralgia.

Diagnostic nerve block: An intercostal block is often performed to determine if an intercostal nerve is involved in the generation of chest wall pain. If an intercostal block via a single injection is able to provide temporary pain relief, it indicates that the intercostal nerve is likely a component of that pain pathway. Subsequently, a neurolytic block, cryoablation, radiofrequency ablation, or chemical neurolysis can be performed in the same intercostal segment to relieve pain for an extended period of time.

Technique

An intercostal nerve block can be performed with the patient in a sitting, prone, or lateral decubitus position and the intended block region upward. Sedation is optional and can be achieved with a combination of a benzodiazepine, a short-acting narcotic such as fentanyl, and/or ketamine.

The insertion site for an intercostal nerve block is usually just below the lower edge of the rib, slightly medial to the posterior axillary line, and 6 to 8 cm lateral to the respective vertebral spinous process. If the insertion site is too anterior, the lateral cutaneous branch of the intercostal nerve may be missed as it arises at the midaxillary line (see Fig. 31-1).

Fluoroscopic guidance is recommended, but not absolutely necessary for performing intercostal nerve blocks. Under sterile conditions, a skin wheal is made with local anesthesia. A 3.5 inch, 25- (or 22-) gauge needle is inserted over the rib and directed perpendicular to the skin. A 15-degree bend away from the bevel of the needle allows the needle to “steer” (bevel is pointing caudad). Longer needles may be needed for obese patients. When the needle contacts the periosteal surface of the inferior portion of the rib bone, it can be rotated 180 degrees, then slowly “walked off” the rib inferiorly until it just slips off under the rib. The 15-degree bend of the needle tip away from the bevel can facilitate the needle being walked off the rib, with the direction of the bevel cephalad, which then places the bevel of the needle in proximity to the intercostal nerve, (Figs. 31-3 through 31-5) where it is known to lie in the intercostal groove as the classic VAN complex (vein, artery, nerve from cephalad to caudad) (see Fig. 31-2). Another helpful technique is to manually retract the skin superiorly prior to needle insertion, which allows the needle to automatically move inferior when the needle contacts bone. This maneuver reduces needle motion and rotation.² When the lower rib margin is identified, the needle is then advanced 2 to 3 mm to reach the intercostal groove. After negative aspiration for blood and air, a mixture of 1 to 5 mL of lidocaine or bupivacaine with or without 1: 200,000 epinephrine and/or corticosteroid is injected. The procedure can be repeated in other intercostal segments. Due to collateral innervation, blockade of at least three adjacent segments is often needed to ensure anesthesia/analgesia in the distribution of the middle intercostal nerve.

Figure 31-3 Needle placement in right T12 intercostal groove after “walking off” inferior edge of T12 rib.

Figure 31-4 Contrast spread in right T12 intercostal groove.

Figure 31-5 Washout of contrast along the T12 right intercostal nerve in the intercostal groove.

For a neurolytic intercostal nerve block, sequential injection technique is used to avoid pain induced by neurolytic agents. The intercostal nerve is first blocked with 3 to 5 mL of 0.5% bupivacaine with 1: 200,000 epinephrine injected on its proximal site, followed by another injection of a neurolytic agent (e.g., 2 to 3 mL of 100% alcohol) on a site distal to the anesthetized site.

To perform a continuous intercostal nerve block, a catheter is placed through a 17-gauge epidural needle. The insertion site is the same as for a single injection, that is, below the lower edge of the rib, close to the posterior axillary line, and 6 to 8 cm lateral to the respective vertebral spinous process. To obtain maximal coverage, the insertion site should be in the middle of the segments to be blocked. The bevel of the Touhy needle is oriented medially and the tip of epidural catheter is directed medially. After 10 mL of anesthetic solution is injected through the epidural needle, an intercostal catheter is advanced 2 cm and then secured to the skin.³ Appropriate spread of local anesthetics can be confirmed by radiographic imaging with the use of a nonionic contrast agent prior to local anesthetic injection to rule out subarachnoid, intravascular, or pleural placement.

Complications

The major complications of an intercostal nerve block are pneumothorax and intravascular injection of local anesthetics. Careful postprocedure monitoring is necessary to detect these complications.

The incidence of clinical significant pneumothorax has been reported less than 0.1%.^4,5 Careful attention to technique, smaller-gauge needles, use of fluoroscopic guidance, and avoidance of vigorous needle advancement or probing may help decrease the incidence of this complication.

Accidental intravascular injection of local anesthetics during intercostal block is uncommon but potentially serious. It is known that blood levels of local anesthetics after an intercostal nerve block are significantly greater than those after other frequently performed regional anesthetic techniques.⁶ Adding epinephrine to local anesthetics and aspirating for blood before administering anesthetics, as well as injection of nonionic contrast under continuous fluoroscopy, are important steps that can be taken to minimize intravascular injection of local anesthetics.

Other rare complications associated with an intercostal nerve block include infection, hemothorax, hemoptysis, hematoma, tissue necrosis, neuritis, respiratory insufficiency, subarachnoid block, failed block, and allergic reaction to local anesthetics.⁷ If nonionic contrast is used, anaphylactoid reactions can occur, but are rare, and can be avoided by a pretreatment regimen of prednisone, diphenhydramine, and ranitidine.⁸

Other Treatments

Acute and chronic pain states treated with intercostal nerve block may also be managed with other approaches such as paravertebral block, interpleural block, or thoracic epidural steroid injections, transcutaneous electrical nerve stimulation (TENS), physical therapy, topical anesthetics/NSAIDs, spinal cord stimulation, tricyclic antidepressants, and anticonvulsants.

Conclusion

Intercostal nerve block can be a useful intervention for acute and/or chronic pain in the chest wall. This chapter reviews the block technique with and without image guidance, and describes a safe and effective technique to provide short- and long-term pain relief for a variety of chest wall pain syndromes.