Intercostal nerve block is a technique of producing somatosensory and motor blockade on the chest and abdominal wall. This technique can be used for pain control in thoractomy, mastectomy and rib fractures. Lower intercostal nerve blocks may also be used for pain relief for upper abdominal surgeries.
Intercostal nerves are the anterior rami of the first 11 thoracic spinal nerves (the anterior ramus of the 12th thoracic nerve lies in the abdomen as the subcostal nerve).
Course of intercostal nerves:
Each intercostal nerve enters the corresponding intercostal space between the posterior intercostal membrane and the parietal pleura. The nerve then forwards with the intercostal vessels in the subcostal groove of the corresponding rib between the innermost intercostal and internal intercostal muscles. The first six intercostal nerves give branches and terminate within their respective intercostal spaces. Seventh, eighth and ninth leave their intercostal spaces anteriorly (after innervating the structures within) and pass to the anterior abdominal wall. The tenth and eleventh ribs pass directly into the abdominal wall because of the fact that the corresponding ribs are floating
Each intercostal nerve gives numerous branches that are elaborated below;
Rami communicantes: These connect the intercostal nerves to a ganglion of sympathetic trunk that lies adjacent to the vertebral column on both sides.
Collateral branch: It runs parallel to the main nerve on the upper border of the rib below.
Lateral cutaneous branch: It innervates the skin on the side of the thoracic wall by dividing into anterior and posterior branches.
Anterior cutaneous branch: It is the terminal portion of the intercostal nerves and innervates the skin near the midline of chest by dividing into medial and lateral branches.
Muscular branches: All the muscles of the intercostal spaces are innervated by the various muscular braches of intercostal nerves.
Pleural branches: These are sensory branches that go to the parietal pleura.
Peritoneal sensory branches: These are similar to the pleural sensory branches but arise from the lower intercostal nerves because the lower intercostal spaces are more related to the peritoneum that to parietal pleura.
First intercostal nerve : It is joined to the brachial plexus through a branch, which is equivalent to the lateral cutaneous branches of remaining intercostal nerves. Another exception with the first intercostal nerve is that there is no anterior cutaneous branch
Second intercostal nerve: It is joined to the medial cutaneuos nerve of the arm by a branch called the intercostobrachial nerve. This branch is equivalent to the lateral cutaneuos branch of the remaining nerves. In this way the second intercostal nerve supplies not only the second intercostal space, but also the skin of the armpit and the upper medial side of the arm.
Pattern of innervation of intercostal nerves:
Excluding the exceptions stated above, there is a general pattern of innervations of intercostal nerves. T1 to T6 intercostal nerves supply the following structures related to respective intercostal spaces:
- Parietal pleura
- Intercostal muscles
- serratus posterior muscles
T7 to T11 intercostal nerves supply the following structures:
- Parietal peritoneum
- Anterior abdominal muscles including the external oblique, internal oblique, transversus abdominis and rectus abdominis muscles.
Intercostal block produces discrete band-like segmental anesthesia in the chosen levels. The beneficial effect of intercostal blockade on respiratory function following thoracic or upper abdominal surgery, or following chest wall trauma is well known. Although similar in many ways to the paravertebral block, intercostal blocks are generally simpler to perform because the osseous landmarks are more readily palpable. However, the risks of pneumothorax and local anesthetic systemic toxicity are present, and care must be taken to prevent these potentially serious complications. Intercostal blocks can be more challenging to perform above the level of T7 because the scapula prevents access to the ribs. Although an intercostal block is an excellent choice for analgesic purposes, it is often inadequate as a complete surgical anesthesia. For this application, supplementation with another anesthesia technique usually is required.
Intercostal blockade results in the spread of local anesthetic along the intercostals sulcus underneath the parietal pleura, leading to ipsilateral anesthesia of the blocked intercostals levels. A larger volume of local anesthetic or more medial injection may result in backtracking of local anesthetic into the paravertebral space.
The important surface anatomic landmarks are:
- Manubriosternal joint = T2
- Nipple line = T4
- Xiphoid process = T6
- Umbilicus = T10
- Symphysis pubis = T12
An intercostal block can be performed with the patient in the sitting, lateral decubitus, or prone position.
The intercostal nerve can be readily blocked at the angle of the rib just lateral to the sacrospinalis muscle group. . Patients who are prone are best positioned for the block by placing a pillow under the abdomen and with the arms hanging down from the sides of the bed. This rotates the scapulae laterally and permits access to the angles of the rib above the level of T7
The vertebral spines of the level of the corresponding ribs are marked. The posterior angles of the rib, which can be palpated 6 to 8 cm from the midline are also marked. The inferior edge of each rib is palpated and marked on a line intersecting the posterior angle of the rib. After appropriate skin preparation, skin wheals are raised at each of these points with local infiltration. A 22or 23-gauge, short-beveled needle attached to a 10-mL syringe via a 10 cm extension tubing can be used. Beginning at the lowest rib, the index finger of the left hand displaces the skin up over the patient’s rib. The needle is inserted at a 20 degree angle at the tip of the finger until it rests on the rib. Contact with the rib should be made at within 1 cm in most patients. While maintaining the same angle of insertion, the needle is walked off the inferior border of the rib as the skin is allowed to return to its initial position. Then the needle is advanced 3 mm below the inferior margin of the rib, with the goal of placing the tip in the space containing the neurovascular bundle i.e., between the internal and innermost intercostal muscles. The end point for advancement should be the predetermined distance (3-5 mm). Following negative aspiration for blood or air, 2-5 mL of local anesthetic is injected. The process is repeated for the remaining levels of blockade
With the patient in sitting or lateral position, it is helpful to have the patient’s spine arched with the arms extended forward
Injection of 1 to 2 mL of solution as the needle is withdrawn blocks the subcutaneous branches. The major complication feared with intercostal blockade is pneumothorax. The actual incidence, however, was as low as 0.07% in a large series performed by anesthesiologists at all levels of training. Routine postoperative chest radiographs showed a 0.42% incidence of nonsymptomatic pneumothorax. If this unusual complication occurs, treatment is usually limited to observation, administration of oxygen, or needle aspiration. Rarely, chest tube drainage is required when these treatments are unsuccessful.
A risk of systemic local anesthetic toxicity is present with multiple intercostal blocks because of the large volumes and rapid absorption of the solutions. Use of epinephrine has been shown to decrease blood levels. Patients should be monitored and observed carefully during the block and for at least 20 to 30 minutes afterward. An interpleural block should not be performed in patients with pleural fibrosis or inflammation, pleural effusion, lung parenchymal disease associated with pleural disease, or bleeding diatheses. Pleural disease can result in poor spread of local anesthetic solutions or rapid uptake in the case of inflammation. Patients with severe pulmonary disease who rely on their intercostal muscles may exhibit respiratory decompensation after bilateral intercostal blockade.
USG guided technique
The chest wall is best imaged in a coronal (vertical) plane in the same area as would for an intercostal block by landmark technique ie about 5cm lateral to the spinous process to visualize the intercostal space in the short axis view. The relevant intercostal space is visualized by using a 6-13 MHz linear transducer. The ribs appear as dense dark oval structures with a bright surface (periosteum). The pleura and lungs are visualized deep to the intercostal space between the echo shadows.
The parietal pleura appears in between the ribs as a glistening white hyperechoiec structure sliding with respiration.
The needle is passed in plane to the ultrasound beam till the needle tip penetrates the internal intercostal membrane. The drug is deposited between the innermost and inner intercostals muscles with the end point of the injection being the downward displacement of the pleura.
Drug Dosage-2 -5 ml of LA can be injected at each level keeping in mind toxic level of the LA if multiple levels are to be blocked.