• Manoj K. Karmakar, MD

       INTRODUCTION

The intercostal nerves (ICNs) innervate the major parts of the skin and musculature of the chest and abdominal wall. The block of these nerves was first described by Braun in 1907, in the textbook Die Lokalanästesie.¹ In the 1940s, clinicians noticed that intercostal nerve blocks (ICNBs) could favorably effect a reduction in pulmonary complications and in narcotic requirements after upper abdominal surgery.¹ In 1981, continuous ICNB was introduced to overcome the problems associated with repeated multiple injections.¹ Today, ICNB is used in a great variety of acute and chronic pain conditions affecting the thorax and upper abdomen. Less commonly, it is also used for breast and minor chest wall surgery and, in combination with celiac plexus blockade, abdominal operations, usually with light sedation or general anesthesia. As with many other regional techniques, the advantages of ICNBs include superior analgesia, opioid-sparing effect, improved pulmonary mechanics, reduced central nervous system depression, and avoidance of urinary retention. It should be noted, however, that supplemental systemic analgesia is also almost always needed. The disadvantages of the technique include the requirement for technical expertise, risks of pneumothorax, and local anesthetic toxicity with multiple levels of blockade.

       INDICATIONS

ICNB provides excellent analgesia for chest trauma such as rib fractures^{2, 3} and for postsurgical pain after chest and upper abdominal surgery such as thoracotomy, thoracostomy, mastectomy, gastrostomy, and cholecystectomy.⁴ Respiratory parameters typically improve with relief of pain.^{2, 3} Blockade of the two dermatomes above and the two below the level of surgical incision is required. ICNB does not block visceral abdominal pain, for which a celiac plexus block is required. It is inadequate for renal surgery since a block from T5 to L3 is required. In itself, ICNB alone does not provide adequate intraoperative anesthesia, and supplemental analgesics or sedatives are usually required except for minor body surface surgery. Neurolytic ICNB maybe used to manage chronic pain conditions such as postmastectomy pain (T2) and postthoracotomy pain.

       CONTRAINDICATIONS

       FUNCTIONAL ANATOMY

As thoracic nerves Tl to T12 emerge from their respective intervertebral foramina, they divide into the following rami (Figure 44–1):

        T1 and T2 send nerve fibers to the upper limbs and the upper thorax, T3 through T6 supply the thorax, T7 through Til supply the lower thorax and abdomen, and T12 innervates the abdominal wall and the skin of the front part of the gluteal region (Figure 44–2). Carrying both sensory and motor fibers, the ICN pierces the posterior intercostal membrane about 3 cm (in adults) distal to the intervertebral foramen to enter the subcostal grove where it, for the most part, continues to run parallel to the rib although branches may often be found anywhere between adjacent ribs. Its course within the thorax is sandwiched between the parietal pleura and innermost intercostal (also called the intercostalis intimus) muscles (inwardly) and the external and internal intercostal muscles (outwardly) (Figures 44–3 and 44–4). lust anterior to the midaxillary line, it gives off the lateral cutaneous branch. As the ICN approaches the midline, it turns anteriorly and pierces the overlying muscles and skin to terminate as the anterior cutaneous. There are notable variations. The first thoracic nerve (Tl) has no anterior cutaneous branch, usually has no lateral cutaneous branch, and most of its fibers leave the intercostal space by crossing the neck of the first rib to join those from C8, while a smaller bundle continues on a genuine intercostal course to supply the muscles of the intercostal space. Some fibers of T2 and T3 give rise to the intercostobrachial nerve, which innervates the axilla and the skin of the medial aspect of the upper arm as far distal as the elbow. In addition, the ventral ramus of T12 is similar to the other ICNs but is called a subcostal nerve because it is not positioned between two ribs.

Figure 44–1. Anatomy of the spinal nerve.

Lateral Cutaneous Branch

From their origins just anterior to the midaxillary line, the lateral cutaneous branches of T2 through T11 pierce the internal and external intercostal muscles obliquely before dividing into the anterior and posterior branches (see Figure 44–4). These branches supply the muscles and skin of the lateral torso. The anterior branches supply of T7 to Til innervate the skin as far forward as the lateral edge of the rectus abdominis. The posterior branches of T7 to Til supply the skin overlying the latissimus dorsi. The lateral cutaneous branch of T12 does not divide. Most of the ventral ramus of Tl 2 joins that of LI to form the iliohypogastric, ilioinguinal, and genitofemoral nerves; the remaining part pierces the transverse abdominal muscle to lie between it and the internal oblique muscle.

Figure 44–2. Dermatomal distribution of the intercostal nerves.

Figure 44–3. Intercostal nerves (accompanied by intercostal artery and vein) shown in the intercostal sulcus as seen from within the open chest cavity in a cadaver. The red dye illustrates spread of solutions injected into the intercostal sulcus during intercostal block. 1 .Intercostal nerve. 2. Distribution of the dye after injection into the intracostal sulcus.

Anterior Cutaneous Branch

The anterior cutaneous branches of T2 through T6 pierce the external intercostals and pectoralis major muscles to enter the superficial fascia near the lateral border of the sternum to supply the skin of the anterior part of the thorax near the midline and slightly beyond (see Figure 44–4). Smaller branches (Tl through T6) exist to supply the intercostal muscles and parietal pleura, and these branches may cross to adjoining intercostal spaces. The anterior cutaneous branches of T7 through T12 pierce the posterior rectus sheath to supply motor nerves to the rectus muscle and sensory fibers to the skin of the anterior abdominal wall. Some final branches of T7 through T12 continue anteriorly and, together with LI, innervate the parietal peritoneum of the abdominal wall. Their anterior course continues and becomes superficial near the linea alba to provide cutaneous innervation to the midline of the abdomen and a couple of centimeters beyond.

       MECHANISM OF BLOCK & DISTRIBUTION OF ANESTHESIA

ICNB blocks the ipsilateral sensory and motor fibers of the ICNs by a direct effect of the local anesthetic. Three milliters of solution injected through a needle spreads easily for some 4–6 cm along that single subcostal groove distally and proximally (see Figure 44–3). If a catheter is inserted at the angle of the rib and directed medially 2–3 cm, the tip of the catheter will lie medial to the medial border of the intercostalis intimus muscle; 20 mL of solution can spread to the paravertebral space to contact 3–5 ICNs.

Figure 44–4. Anatomy of the intercostal nerve.

       TECHNIQUE

As with any regional block, some basic safety rules apply. The patient’s airway and breathing must first be assessed and monitored. An intravenous line should be established, and resuscitation drugs should be readily available. Sedation and analgesia may be used in selected cases. Supplemental oxygen may be required. During the block, the clinician’s hand controlling the needle should be firmly in contact with the patient’s body. ICNB may be performed in an anesthetized patient, although spinal anesthesia has been reported in patients when ICNB was performed under general anesthesia,⁴ and there is a concern that the risk of pneumothorax may be increased in a patient under positive pressure ventilation. After the block, the patient should be monitored for potential complications. In the case of ICNB, they include pneumothorax, local anesthetic toxicity, hematoma, nerve damage, infection, and, rarely, spinal anesthesia.

        The ICN can be blocked anywhere proximal to the midaxillary line, where the lateral cutaneous branch originates. In children, the block is commonly carried out at the posterior axillary line or, alternatively, just lateral to the paraspinal muscles, at the angle of the rib. In adults, the most popular site for ICNB is at the angle of the rib (6–8 cm from the spinous processes, Figures 44–5). Blocking the ICN at this location is relatively easy, is unlikely to result in direct injection into the durai sheath, and ensures that the tissues innervated by the lateral cutaneous nerve are blocked. At the angle of the rib, the rib is relatively superficial and easy to palpate, and the subcostal groove is the widest, theoretically reducing the probability of pleural puncture. Within this groove, the nerve is inferior to the posterior intercostal artery, which is inferior to the intercostal vein (Figures 44–6 and 44–3) (Mnemonic: VAN (vein/artery/nerve). They are surrounded mainly by adipose tissue and are sandwiched between the internal intercostal and the innermost intercostal (intercostalis intimus) muscles. The nerve often runs as three or four separate bundles, without an enclosing endoneural sheath, making it easily accessible to blockade. Blockade medial to the angle of the rib is not recommended because the nerve lies deep to the posterior intercostal membrane with very little tissue between it and the parietal pleura, and the overlying sacrospinalis muscle makes rib palpation difficult. Blockade distal to the anterior axillary line is more difficult because the nerve has left the subcostal groove, reentered the intercostal space and lies in the substance of the internal intercostal muscle.

Figure 44–5. The sitting patient should lean slightly forward and be supported. The arms should pull the scapulae laterally to facilitate access to the posterior rib angles above T7. The inferior edges of the ribs to be blocked are marked just lateral to the lateral border of the sacrospinalis (paraspinous) muscle group, corresponding to the angles of the ribs. Points of needle entry are marked at 6–8 cm from the midline in most adults.

Figure 44–6. Needle angle required to enter intercostal sulcus. Note the relationship of the intercostal vessels to the nerve (Superior-to-inferior, VAN: V = vein, A = artery, N = nerve).

        ICNB can be performed with the patient in the prone, sitting, or lateral position (block side up), with due considerations given to age, mental, physical, and ventilatory status, along with any other concomitant blocks contemplated. For the prone position, a pillow should be placed under the patient’s upper abdomen, and the arms are allowed to hang off the sides. The sitting patient should lean slightly forward holding a pillow and be supported. The arms should be forward. The position of the arm in either position is to pull the scapulae laterally and facilitate access to the posterior rib angles above T7 (see Figure 44–5).

        Under aseptic conditions, the block sites are identified. Rib counting, if required, can be achieved by starting from the twelfth rib, or from the seventh rib, which is the lowest rib covered by the inferior tip of the scapula. The inferior edges of the ribs to be blocked are marked just lateral to the lateral border of the sacrospinalis (paraspinous) muscle group (usually 6–8 cm from the midline at the lower ribs and 4–7 cm from the midline at the upper ribs), corresponding to the angles of the ribs. Next, palpate the inferior borders of the ribs to be blocked and mark them, (see Figure 44–5).

        The sites of skin entry are infiltrated with a small volume of lidocaine 1–2%. A site of entry is well-placed when a needle introduced through it at 20 degrees cephalad (sagittal plane; see Figure 44–6) just scrapes underneath the inferior border of the rib and reaches the subcostal groove. The skin is first drawn cephalad with the palpating hand by about 1 cm, and a 4- to 5-cm, 22- to 24-gauge (for singleshot injection), short-beveled needle is introduced through the chosen entry site at a 20-degree cephalad angle with the bevel facing cephalad. The needle is advanced until it contacts the rib (at a depth of less than 1 cm in most patients). A small amount of local anesthetic may be injected to anesthetize the periosteum. With the palpating hand holding the needle firmly and resting securely on the patient’s back, the injecting hand gently walks the needle caudally while the skin is allowed to move back over the rib (Figure 44–7).

The needle is now advanced 3 mm, still maintaining the 20-degree tilt angle cephalad (even a slight caudad-pointing angle by the needle greatly reduces the chance of success). A subtle “give” or “pop” of the fascia of the internal intercostal muscle may be felt, especially if a short-beveled needle is used. As the average distance from the posterior aspect of the rib to the pleura averages 8 mm, advancement of the needle much beyond 3 mm increases the risk of pneumothorax.⁵

Figure 44–7. With the palpating hand holding the needle firmly and resting securely on the patient’s back, the injecting hand gently walks the needle caudally while the skin is allowed to move back over the rib.

        Paresthesia, although not actively sought, confirms needle placement. Radiologic guidance is advised for neurolytic blocks. At this point, on negative aspiration for blood, 3–5 mL of local anesthetic is injected. For a single ICNB, it is desirable to block at least one ICN cephalad and one caudad because some degree of overlapping innervation from adjacent ICNs is common. To ensure that the tip of the needle remains in the optimal location, unaffected by hand and chest movement, some clinicians prefer to connect an extension tubing between the needle and the syringe and have an assistant perform the aspiration and injection.

        When repeated injections at multiple levels are desired, patient comfort, the increased risk of complications and convenience become important issues, and a continuous ICNB should be considered. The technique is the same as for a single-injection block except that a Tuohy 17- or 18-gauge needle (in adults) is used to facilitate the placement of a catheter. The site of entry should be the intercostal space midway between the dermatomes to be blocked. By orientating the bevel of the Tuohy needle medially or laterally, the epidural catheter is directed medially or laterally, respectively. A catheter tip threaded medially by 3 cm would effect a paravertebral block; the local anesthetic injected can spread to the adjacent spaces involving three to five intercostal spaces in total if sufficient volume (eg, 20 mL) is used. In contrast, solution injected via a laterally directed catheter tends to stay mainly in the same intercostal groove. A lesser degree of spread may be possible because the intercostalis intimus muscle is flimsy, and local anesthetic can pass between the separate fascicles of that muscle to reach the subpleural space, from where it can spread between ribs and pleura to reach adjacent ICNs.⁵ It is usually difficult to thread a catheter much beyond 3 cm. Ability to pass a catheter beyond several centimeters suggests that the catheter may be within the pleura. It is also common for continuous intercostal block catheters to be placed under direct vision by surgeons at the end of a thoracotomy and before wound closure.⁶

        Blockade of Tl through T7 is made more difficult because of the scapulae and the rhomboid muscles. Fortunately, few surgeries require blockade above T7. We prefer to perform a thoracic paravertebral block or an epidural blocks when high thoracic blockade is required.

        ICNB, either single-shots or continuous, may actually result in injection of local anesthetic or catheter placement into the interpleural space or pulmonary parenchyma. Great ease of catheter insertion beyond 3 cm may suggest interpleural placement. Although analgesia may be provided with interpleural analgesia, it will not be the case with intraparenchymal injection.

       EQUIPMENT

        Needle: Single-shot: 20- to 22-gauge short-beveled 4- to 5-cm needle (adults)

        Catheter placement: 18-to 20- gauge Tuohy needle (adults)

        Syringe and needle for local infiltration

        Syringe with extension tubing

        Sterilizing and resuscitation equipment and drugs, drapes, marking pen, pillow, portable fluoroscope (for neurolytic blocks)

       CHOICE OF LOCAL ANESTHETIC

The choice of local anesthetic for single-shot ICNB includes bupivacaine 0.25–0.5%, lidocaine 1–2% with epinephrine 1/200,000–1/400,000, and ropivacaine 0.5–0.75%. Three to 5 mL of local anesthetic is injected at each level during a multiple-injection ICNB. The duration of action is usually 12 ± 6 h. Addition of epinephrine to bupivacaine or ropivacaine does not significantly prolong the duration of block, but may slow the systemic absorption and increase the maximum allowable dose with a single shot by 30%.⁴ Maximum bupivacaine dose is 2 (for plain solution) to 3 (with epinephrine) mg/kg/injection (total at one time)⁷ and 7–10 mg/kg/day. Maximum lidocaine dose is up to 5 (for plain solution) and 7 (with epinephrine) mg/kg/single injection⁷ and 20 mg/kg/day. Volunteers have been found to tolerate 30% more ropivacaine than bupivacaine before neurologic symptoms develop.⁸ The maximum single injection dose for ropivacaine is 2.5 mg/kg (for plane solution) and 4 mg/kg (with epinephrine),⁷ and the daily dose should probably be < 9–12 mg/kg/24 h. The maximum single injection of epinephrine in stable patients is 4 mcg/kg. Depending on the volume of local anesthetic required, a 1/400,000 instead of 1/200,000 concentration of epinephrine may be chosen. Richly supplied areas favor rapid local anesthetic absorption, and the blood levels of local anesthetics after ICNB are higher than for any other regional anesthetic procedure. As such, it is advisable to leave a safety margin between the doses given and the maximum recommended dosages, especially in young children, the elderly, debilitated patients, and those with underlying cardiac, hepatic, or renal impairment. For continuous infusion, patients can usually tolerate a gradual build-up of the plasma local anesthetic level better than acute rises. An apparently safe regimen is a loading dose of 0.3 mL/kg followed by an infusion of 0.1 mL/kg/h of either bupivacaine 0. 25% or lidocaine 1%.⁵

Clinical Pearls

Related posts:

Regional Anesthesia in the Patient with Preexisting Neurologic Disease. The History of Local Anesthesia. Stimulating Catheters. Ultrasound-Assisted Nerve Blocks in Adults. Cutaneous Blocks for the Upper Extremity. Cervical Plexus Block.

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