Patient Selection

All patients are candidates for this block, although as patients become more obese the blocks are technically more difficult to carry out.

Pharmacologic Choice

As with any decision about local anesthetic choice, it must be decided whether motor blockade will be required for a successful block. If intercostal nerve block is combined with light general anesthesia for intra-abdominal surgery and the intercostal block is prescribed to provide abdominal muscle relaxation, a higher concentration of local anesthetic will be needed. In this setting, 0.5% bupivacaine or ropivacaine, 1.5% lidocaine, or 1.5% mepivacaine is an appropriate choice. Conversely, if sensory analgesia is all that is necessary from the block, then 0.25% bupivacaine, 0.2% ropivacaine, 1% lidocaine, or 1% mepivacaine is appropriate.

Anatomy

The intercostal nerves are the ventral rami of T1 through T11. The 12th thoracic nerve travels a subcostal course and is technically not an intercostal nerve. The subcostal nerve can provide branches to the ilioinguinal and iliohypogastric nerves. Some fibers from the first thoracic nerve also unite with fibers from C8 to form the lowest trunk of the brachial plexus. The other notable variation in intercostal nerve anatomy is the contribution of some fibers from T2 and T3 to the formation of the intercostobrachial nerve. The terminal distribution of this nerve is to the skin of the medial aspect of the upper arm.

Examination of an individual intercostal nerve shows that there are five principal branches (Fig. 33-1). The intercostal nerve contributes preganglionic sympathetic fibers to the sympathetic chain through the white rami communicantes (branch 1) and receives postganglionic neurons from the sympathetic chain ganglion through the gray rami communicantes (branch 2). These rami are joined to the spinal nerves near their exit from the intervertebral foramina. Also, shortly after exiting from the intervertebral foramina, the dorsal rami carrying posterior cutaneous and motor fibers (branch 3) supply skin and muscles in the paravertebral region. The lateral cutaneous branch of the intercostal nerve arises just anterior to the mid-axillary line before sending subcutaneous fibers posteriorly and anteriorly (branch 4). The termination of the intercostal nerve is known as the anterior cutaneous branch (branch 5)