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Brown: Atlas of Regional Anesthesia, 3rd ed., Copyright © 2006 Saunders, An Imprint of Elsevier
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PLACEMENT

Anatomy.

The intercostal nerves are the ventral rami of T1–11. 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 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 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 only 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 course, the nerve traverses the intercostal spaces inferior to the intercostal artery and vein of the same space.

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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 is placed under the patient’s mid-abdomen to reduce lumbar lordosis and to accentuate the intercostal spaces posteriorly. The arms are 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 the intercostal nerve block. The midline should be marked from T1 to L5, and then two paramedian lines are drawn at the posterior angle of the ribs. These lines should angle medially in the upper thoracic region, so 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 such as that in Figure 33-2 can be created. Before needle puncture, appropriate intravenous sedation is 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 hand and finger positions illustrated in Figure 33-3 are adhered to and incorporated into the development of each anesthesiologist’s own systematic technique.

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


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


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 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 and the index and middle fingers. It is important that the left hand’s hypothenar eminence is firmly placed against the patient’s back. This hand placement allows maximum 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 2–4 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. It is important to know that 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 , 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 is underutilized. One concern that has been raised with the lateral approach to the intercostal nerve is that the lateral cutaneous branch of the intercostal nerve might be missed. Clinically, this does not seem to be the case, an observation supported by computed tomographic studies showing that injected solutions spread readily along the subcostal groove for a distance of many centimeters. Therefore even when a lateral intercostal block is carried out, the lateral branch should be bathed with local anesthetic solution.

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Figure 33-4  Intercostal nerve block: lateral technique.


Potential Problems.

The principal concern with intercostal nerve block is pneumothorax. Although the incidence of this complication is extremely low, many physicians avoid this block because of the imagined high frequency and seriousness of the complications. Data suggest that the incidence of pneumothorax is less than 0.5%; and even when it occurs, careful clinical observation is usually all that is necessary. The incidence of symptomatic pneumothorax after intercostal block is even lower, at approximately 1:1000. If treatment is deemed necessary, needle aspiration often can be carried out with successful re-expansion of the lung. Chest tube drainage should be performed only if there is a failure of lung re-expansion after observation or percutaneous aspiration.

As a result of the vascularity of the intercostal space, blood levels of local anesthetic are higher for multiple-level intercostal block than for any other standard regional anesthetic technique. Because these peak blood levels may be delayed for 15 to 20 minutes, patients should be closely monitored after the completion of a block for at least that interval.

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