The intercostal nerves (ICNs) supply 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.
Authors
A. M.-H. Ho, MSc, MD, FRCPC, FCCP, FHKCA, FHKAM; M. K. Karmakar, MD, FRCA, DA (UK), FHKCA, FHKAM
Affiliations
Department of Anaesthesia and Intensive Care The Chinese University of Hong Kong Prince of Wales Hospital Shatin, NT Hong Kong SAR PRC Tel: [+852] 2632 2735 Fax: [+852] 2637 2422
The intercostal nerves (ICNs) supply 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 1940’s, 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, improved pulmonary mechanics, reduced central nervous system depression, and avoidance of urinary retention. It should be noted however, that supplemental systemic analgesia is also always needed. The disadvantages of the technique however, include the requirement for technical expertise, risks of pneumothorax, and local anesthetic toxicity with multiple levels of blockade.
ICNB provides excellent analgesia for chest trauma such as rib fractures,7,8 and for after chest and upper abdominal surgery such as thoracotomy, thoracostomy, mastectomy, gastrostomy, and cholecystectomy.2 Respiratory parameters typically show impressive improvements upon removal of pain.7,8 Blockade of two dermatomes above and 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 as block from T5 to L3 are required. In itself, ICNB does not provide adequate intraoperative anesthesia, and supplemental analgesics and/or sedatives are usually required except for minor body surface surgery. Neurolytic ICNB may be used to manage chronic pain conditions such as post-mastectomy pain (T2) and post-thoracotomy pain.
When pneumothorax would be a disaster. ICNBs may help a patient tethering on the brink of respiratory decompensation but if an unintended pneumothorax could have serious consequences, an alternative block should be considered unless a chest tube is in place.
Hemostatic deficiencies. This contraindication is not as strong as in central neuraxial blocks but may become absolute if the degree of deficiencies is severe.
Other contraindications typically associated with regional blocks. Local infection, lack of expertise and resuscitating equipments, and lack of any short-term plan to wean from the ventilator should discourage the use of this block.
As thoracic nerves T1 to T12 emerge from their respective intervertebral foramena, they divide into (Figure 1):
the paired gray and white anterior rami comunicans, which pass anteriorly to the sympathetic ganglion and chain;
the posterior cutaneous ramus, supplying skin and muscle in the paravertebral region;
the ventral ramus (ICN, the main focus of this article).
Figure 3.Intercostal nerves (accompanies 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 Figure 4.Intercostal nerve: Course and division.
Figure 1.Clinical anatomy of an intercostal nerve with its surrounding structures. Figure 2.Dermatomal distribution of the intercostal nerves.
T1 and T2 send nerve fibers to the upper limbs and the upper thorax, T3-T6 supply the thorax, T7-T11 supply the lower thorax and abdomen, and T12 innervates the abdominal wall and the skin of the front part of the gluteal region, Figure 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 intercostals (alias intercostalis intimus) muscle (inwardly) and the external and internal intercostals muscles (outwardly) (Figures 3 and 4). Just anterior to the mid-axillary 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. T1 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 rami of T12 is similar to the other ICNs but is called a subcostal nerve because it is not in between two ribs.
Lateral cutaneous branch
From their origins just anterior to the mid-axillary line, the lateral cutaneous branches of T2-T11 pierce the internal and external intercostals muscles obliquely before dividing into the anterior and posterior branches, Figure 4. These branches supply the muscles and skin of the lateral torso. The anterior branches supply of T7 to T11 supply the skin as far forward as the lateral edge of the rectus abdominis. The posterior branches of T7 to T11 supply the skin overlying the latissimus dorsi. The lateral cutaneous branch of T12 does not divide. Most of the ventral ramus of T12 joins that of L1 to form the iliohypogastric, ilio-inguinal and genitofemoral nerves; the rest pierces the transverse abdominal muscle to lie between it and the internal oblique muscle.
Anterior cutaneous branch
The anterior cutaneous branches of T2-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, Figure 4. Smaller branches (T1-T6) exist to supply the intercostals muscles and parietal pleura and these branches may cross to adjoining intercostals spaces. The anterior cutaneous branches of T7-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-T12 continue anteriorly, and, together with L1, innervate the parietal peritoneum of the abdominal wall. Their anterior course continues and become superficial near the linea alba, to provide cutaneous innervation to the midline of the abdomen and a couple of cm beyond.
ICNB blocks the ipsilateral sensory and motor fibers of the ICNs by a direct effect of the local anesthetic. Three mL of solution injected through a needle spreads some 4-6 cm easily along that single subcostal groove distally and proximally, Figure 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 5. Palpation of the intercostal space and needle insertion to contact the inferior edge of the rib.
As with any regional block, there are some basic safety rules. 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,2 and there is a concern that if the patient is under positive pressure ventilation, the risk of pneumothorax may be increased. 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.
Figure 6: Intercostal block: Needle angle required to enter intercostal sulcus.
The ICN can be blocked anywhere proximal to the mid-axillary line, where the lateral cutaneous branch originates. In children, the block is commonly carried out at the posterior axillary line or, alternatively, at 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, Figure 5). Blocking the ICN at this location is relatively easy, is unlikely to result in direct injection into the dural 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, Figure 6 (Mnemonics: VAN (vein/artery/nerve)). They are surrounded mainly by adipose tissue and are sandwiched in between the internal intercostals muscle and the interior intercostal (intercostalis intimus) muscle. 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 intercostals membrane with very little tissue between it and the parietal pleura, while 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 and re-entered the intercostals space and lies in the substance of the internal intercostal muscle.
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 statuses, and 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 (Figure 5).
Under aseptic condition, the block sites are identified. Rib counting, if required, can be achieved by starting from the 12th rib, or from the 7th 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, Figure 5. Next, palpate the inferior borders of the ribs one needs to block, and mark them (Figure 7).
Figure 7:Intercostal block: Points of needle insertion.
Figure 8:Intercostal block: Advancement of the needle as the needle walks off the inferior edge of the rib and enters intercostal sulcus.
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° cephalad (sagittal plane, Figure 7) 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 one cm, and a 4-5-cm 22G to 24G (for single shot injection) short-bevel needle is introduced through the chosen site of entry at a 20° cephalad angle and with the bevel facing cephalad (Figure 7). The needle is advanced until it contacts the rib at a depth of less than 1 cm for most non-obese 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 8). The needle is now advanced 3 mm, still maintaining the 20° 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-bevel 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.3
Paresthesia, while not actively sought, confirms needle placement. Radiologic guidance is advised for neurolytic blocks. At this point, upon 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 as 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 intercostal nerve block should be considered. The technique is the same as for a single injection except that a Tuohy 17-G or 18-G 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 3-5 intercostal spaces in total if sufficient volume (e.g., 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 in 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.3 It is usually difficult to thread a catheter much beyond 3 cm. Ability to pass a catheter beyond several cm suggests that the catheter may be interpleural. It is also common for continuous intercostal block catheters to be placed under direct vision by surgeons at the end of a thoracotomy, before wound closure.4
Blockade of T1-T7 is made more difficult because of the scapulae and the rhomboid muscles. Fortunately, few surgeries require blockade above T7. These authors prefer to perform a thoracic paravertebral block or an epidural blocks when high thoracic blockade is required.
ICNB, single-shots or continuous, may actually result in injection of local anesthetic and/or catheter placement into the interpleural space or pulmonary parenchyma. Great ease of catheter insertion beyond 3 cm may suggest interpleural placement. While analgesia may be provided with interpleural analgesia, it will not be the case with intra-parenchymal injection.
The choice of local anesthetic for single shot ICNB include bupivacaine 0.25-0.5%, lidocaine 1-2% with epinephrine 1/200,000-1/400,000 and ropivacaine 0.5-0.75%. 3-5 mL of local anesthetic is injected at each level during a multiple injection ICNB technique. 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%.2 Maximum bupivacaine dose is 2 (for plain solution)-3 (with epinephrine) mg/kg/injection (total at one time)5 and 7-10 mg/kg/day. Maximum lidocaine dose is up to 5 (for plain solution) and 7 (with epinephrine) mg/kg/single injection5 and 20 mg/kg/day. Volunteers have been found to tolerate 30% more ropivacaine than bupivacaine before neurologic symptoms develop.6 The maximum single injection dose for ropivacaine is 2.5 mg/kg (for plane solution) and 4 mg/kg (with epinephrine),5 and the daily dose should probably be <9-12 mg/kg/24 h. The maximum single injection of epinephrine in stable patients is 4 μg/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 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, and those with underlying cardiac, hepatic, or renal impairment. For continuous infusion, patients can usually tolerate a gradual build-up of 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%.3
Clinical Pearls
A relatively easy site for ICNB is the angle of the rib, about 7 cm lateral to midline in adults.
The ideal angle of entry into the subcostal groove is about 20° cephalad.
A continuous catheter may be better tolerated in cases that require repeated blocks at multiple levels.
ICNB provides excellent analgesia but is seldom adequate for intraoperative anesthesia.
Supplemental analgesia may be required in continuous ICNB especially if the area of pain is wide.
Epidural block should be considered as a better alternative to bilateral ICNBs because of the risk of bilateral pneumothorax and the potential for local anesthetic toxicity due the increased amount of local anesthetic required.
Absorption of local anesthetic from the intercostal space is rapid and toxicity is usually an important concern.
ICNB above T7 may be difficult because of the scapulae and an alternative technique such as paravertebral or epidural block should be considered.
The foremost concern in a patient without an ipsilateral tube thoracostomy is pneumothorax, the rate of occurrence of which, as detected by chest X-ray and not necessarily accompanied by signs and symptoms, is well below 1%. Tension pneumothorax and the need for tube thoracostomy are rare. The risks of pneumothorax and lung injury, however, are increased in patients who have had previous chest surgery. If an asymptomatic pneumothorax is detected, the best management is observation, reassurance, and, if necessary, supplemental oxygen.
The peritoneum and abdominal viscera are at risk of penetration when lower ICNs are blocked and the incidence should not be greatly different from that of pneumothorax.
Absorption of local anesthetic from the intercostal space is rapid. Peak arterial plasma concentration develops in <5-10 min, and peak venous plasma concentration peaks several min later. Because of this, toxicity is always a concern with multiple or continuous intercostal injections. Sometimes the dilemma comes when a frail old person has multiple fractured ribs. The concern over systemic anesthetic toxicity may at times necessitate the use of a different regional technique.
Finally, as the dural sheath can extend up to 8 cm laterally, there is a rare chance of spinal anesthesia after an ICNB.
Clinical Pearls
ICNB is indicated for management of acute and chronic pain involving the thorax and upper abdomen.
ICNB by itself is inadequate for most intraoperative anesthesia except for minor body surface surgery.
ICNB is contraindicated when pneumothorax would spell disaster, and in the presence of severe hemostatic deficiencies, and when there are better alternatives.
In the presence of minor hemostatic abnormalities, ICNB may be an attractive alternative to neuraxial blocks. Serious hemostatic deficiencies contraindicate all nerve blocks.
General anesthesia is not a contraindication to ICNB.
Intercostal nerve block is a very satisfying block for both the clinician and patient because it is technically easy to perform and effective in the controlling pain involving the thorax and upper abdomen. It avoids many of the problems associated with central neuraxial blocks. Although there is the risk of pneumothorax and local anesthetic toxicity they can be reduced with good technique and due consideration given to the maximum allowable drug dose and patients clinical condition. The proper use of this technique includes balancing its advantages and disadvantages against those of alternative techniques such as epidural and thoracic paravertebral block.
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Barron DJ, Tolan MJ, Lea RE. A randomized controlled trial of continuous extra-pleural analgesia post-thoracotomy: efficacy and choice of local anaesthetic. Eur J Anaesthesiol 1999; 16:236-45.
Lagan G, McLure HA. Review of local anaesthetic agents. Curr Anaesth Crit Care 2004; 15:247-54.
Scott DB, Lee A, Fagan D, Bowler GM, Bloomfield P, Lundh R. Acute toxicity of ropivacaine compared with that of bupivacaine. Anesth Analg 1989; 69:563-9.
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