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). Medial to the angle of the rib, the intercostal nerve lies between the pleura and the internal intercostal fascia. In the paravertebral region, there is loose areolar and fatty tissue between the nerve and the pleura. At the rib’s posterior angle, the area most commonly used during intercostal nerve block, the nerve lies between the internal intercostal muscles and the intercostalis intimus muscle. Throughout the intercostal nerve’s course, it traverses the intercostal spaces inferior to the intercostal artery and vein of the same space.

Figure 33-1. Intercostal nerve block: cross-sectional anatomy.

Position

To block the intercostal nerve in its preferred location (i.e., just lateral to the paraspinous muscles at the angle of the ribs), the patient ideally is placed in the prone position. A pillow should be placed under the patient’s mid-abdomen to reduce the lumbar lordosis and to accentuate the intercostal spaces posteriorly. The arms should be allowed to hang down from the edge of the block table (or gurney) to permit the scapula to rotate as far laterally as possible.

Needle Puncture

It is advisable to use a marking pen to outline the pertinent anatomy for most regional blocks, and in no block is this more important than in the intercostal nerve block. The midline should be marked from T1 to L5, then two paramedian lines should be drawn at the posterior angle of the ribs. These lines should angle medially in the upper thoracic region so that they parallel the medial edge of the scapula. By successfully palpating and marking the inferior edge of each rib along these two paramedian lines, a diagram like that shown in Figure 33-2 is created. Before needle puncture, appropriate intravenous sedation should be administered to produce amnesia and analgesia during the multiple injections needed for the block. Barbiturates, benzodiazepines, ketamine, or short-acting opioids can be combined. Skin wheals are raised with a 30-gauge needle at each of the previously marked sites of injection, and then intercostal block is carried out bilaterally. As illustrated in Figure 33-3, a 22-gauge, short-beveled, 3- to 4-cm needle is attached to a 10-mL control syringe. It is important that the anesthesiologist adhere to the hand and finger positions illustrated in Figure 33-3 and incorporate them into his or her systematic technique.

Figure 33-2. Intercostal block: position and technique.

Figure 33-3. Intercostal block: stepwise technique (1 to 6).

Beginning at the most caudal rib to be blocked, the index and third fingers of the left hand are used to retract the skin up and over the rib. The needle should be introduced through the skin between the tips of the retracting fingers and advanced until it contacts rib. It is important not to allow the needle to enter to a depth greater than the depth that the palpating fingers define as rib. Once the needle contacts the rib, the right hand firmly maintains this contact while the left hand is shifted to hold the needle’s hub and shaft between the thumb, the index finger, and the middle finger. The left hand’s hypothenar eminence should be firmly placed against the patient’s back. This hand placement allows maximal control of the needle depth as the left hand “walks” the needle off the inferior margin of the rib and into the intercostal groove (i.e., a distance of 2 to 4 mm past the edge of the rib). With the needle in position, 3 to 5 mL of local anesthetic solution is injected. The process is then repeated for each of the nerves to be blocked. In certain patients with cachexia or a severe barrel chest deformity, the intercostal injection can be most effectively carried out with an even shorter 23- or 25-gauge needle.

Intercostal block at the posterior angle of the rib is not the only method applicable to clinical regional anesthesia. As outlined in Chapter 32, Breast Block, intercostal block also can be effectively carried out at the mid-axillary line while the patient is in a supine position (Fig. 33-4). This position is clinically more convenient in many situations and probably underused. Some anesthesiologists are concerned that the lateral approach to the intercostal nerve may miss the lateral cutaneous branch of the intercostal nerve. This does not seem to be the case clinically, and computed tomographic studies show that injected solutions spread readily along the subcostal groove for a distance of many centimeters. Therefore, even when lateral intercostal block is carried out, the lateral branch should most often be bathed with local anesthetic solution.

Figure 33-4. Intercostal block: lateral technique.