FIGURE 24-1. Intercostal nerve block: Patient position and needle insertion.
Intercostal block produces discrete bandlike segmental anesthesia in the chosen levels. Intercostal block is an excellent analgesic option for a variety of acute and chronic pain conditions. The beneficial effect of intercostal blockade on respiratory function following thoracic or upper abdominal surgery, or following chest wall trauma, is well documented. 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.
Regional Anesthesia Anatomy
After emerging from their respective intervertebral foramina, the thoracic nerve roots divide into dorsal and ventral rami (Figure 24-2). The dorsal ramus provides innervation to the skin and muscle of the paravertebral region; the ventral ramus continues laterally as the intercostal nerve. This nerve then pierces the posterior intercostal membrane approximately 3 cm lateral to the intervertebral foramen and enters the subcostal groove of the rib, where it travels inferiorly to the intercostal artery and vein. Initially, the nerve lies between the parietal pleura and the inner most intercostal muscle. Immediately proximal to the angle of the rib, it passes into the space between the innermost and internal intercostal muscles, where it remains for much of the remainder of its course. At the midaxillary line, the intercostal nerve gives rise to the lateral cutaneous branch, which pierces the internal and external intercostal muscles and supplies the muscles and skin of the lateral trunk. The continuation of the intercostal nerve terminates as the anterior cutaneous branch, which supplies the skin and muscles of the anterior trunk, including the skin overlying the sternum and rectus abdominis.
FIGURE 24-2. Anatomy of the thoracic spinal and intercostal nerves.
Distribution of Anesthesia
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 (Figure 24-3). A larger volume of local anesthetic or more medial injection may result in backtracking of local anesthetic into the paravertebral space. The extent of the resulting dermatomal distribution of anesthesia or analgesia is simply a function of the level of blockade. In contrast to paravertebral blockade, longitudinal (cephalad-caudad) spread between adjacent levels is much less common, although possible with large volumes of injectate and/or injection sites close to the midline of the back. In such instances, the local anesthetic can spread between the levels via the overflow into the paravertebral space.
FIGURE 24-3. Injection of the local anesthetic (red dye) in intercostal space results in a medial-lateral spread of the local anesthetic in the intercostal space where the intercostal nerves (arrow) are contained.
A standard regional anesthesia tray is prepared with the following equipment:
• Sterile towels and gauze packs
• 20-mL syringes containing local anesthetic
• Sterile gloves and marking pen
• A 10-mL syringe plus 25-gauge needle with local anesthetic for skin infiltration
• A 1.5-in, 22-gauge needle attached to extension tubing
An intercostal block can be performed with the patient in the sitting, lateral decubitus, or prone positions. With the patient in sitting or lateral position, it is helpful to have the patient’s spine arched with the arms extended forward. 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 (Figure 24-4). This rotates the scapulae laterally and permits access to the angles of the rib above the level of T7 (Figure 24-5).
FIGURE 24-4. The patient position for intercostal block. A pillow is used as an abdominal/pelvic support. The arms are hanging off the table.
FIGURE 24-5. Technique of palpating the intercostal space. The fingers of the palpating hand are firmly pressed in the intercostal space 5–7 cm lateral to the midline.
Landmarks and Maneuvers to Accentuate Them
The following anatomic landmarks are used to estimate the position of the relevant ribs.
1. Twelfth rib (last rib palpable inferiorly) (Figure 24-6)
FIGURE 24-6. Landmarks for intercostal space are identified first by determining the midline and the spinous processes (skin marks). Intercostal space is then determined by palpation at each level to be blocked, and the insertion point for needle is marked 5–7 cm lateral to the midline.
2. The 7th rib (lowest rib covered by the angle of the scapula) (Figure 24-7)
FIGURE 24-7. Estimating T7 level at the tip of the scapula.
Once identified by palpation, the inferior border of the corresponding ribs can be marked on the skin (Figure 24-8). An “x” at the angle of the rib identifies the site of needle insertion, usually about 6–8 cm from the midline. For thoracotomy or upper abdominal incisions, an estimate of the levels required for effective analgesia can be made after discussion with the surgeon as to the planned approach and length of incision. Analgesic blocks for rib fractures are planned based on the area of the injury. Typically, in addition to the estimated dermatomal levels, one additional level above and one below the estimated levels are also blocked.
FIGURE 24-8. The needle insertion site for intercostal space is labeled 5–7 cm lateral to the midline.
• Determining the level of the blockade by counting ribs is merely an estimated, rather than a precise, technique.
After cleaning the skin with an antiseptic solution, 1–2 mL of dilute local anesthetic is infiltrated subcutaneously at each planned injection site.
The fingers of the palpating hand should straddle the insertion site at the inferior border of the rib and fix the skin to avoid unwanted skin movement. A 1.5-in, 22-gauge needle is attached to a syringe containing local anesthetic via extension tubing and advanced at an angle of approximately 20° cephalad to the skin (Figure 24-9). 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 mm).
FIGURE 24-9. Intercostal nerve block: Patient position and needle insertion.
Following negative aspiration for blood or air, 3–5 mL of local anesthetic of insertion and the needle withdrawn. The process is repeated for the remaining levels of blockade.
• A perpendicular or caudad angulation of the needle can cause the block failure; maintenance of the 20° cephalad angle increases the chances that the needle tip will be placed in close proximity to the intercostal nerve.
• Use common sense when advancing the needle. The depth at which the ribs are contacted varies with a patient’s body habitus, and an absence of bony contact at 1 cm should prompt a reevaluation of landmarks rather than continued advancement.
• Never disconnect the needle from the tubing or the syringe containing local anesthetic while the needle is inserted. Instead, use a stopcock to switch the syringes. In the case of inadvertent puncture of the parietal pleura, this strategy prevents the development of a pneumothorax during inspiration, unless the visceral pleura are punctured also.
• In patients with a multiple-level blockade, consider using alkalinized 3-chloroprocaine for skin infiltration to decrease the total dose of the more toxic, long-acting local anesthetic
Choice of Local Anesthetic
It is usually beneficial to achieve longer-acting anesthesia or analgesia for intercostal blockade by using a long-acting local anesthetic. Systemic absorption of local anesthetic is high following an intercostal block, and careful consideration of the dose should precede the block performance to decrease the risk of systemic toxicity.
Table 24-1 lists some commonly used local anesthetic solutions and their dynamics with this block.
Table 24-1 Choice of Local Anesthetic for Intercostal Block
Block Dynamics and Perioperative Management
The performance of intercostal blocks is associated with relatively minor patient discomfort, although needle contact with the periosteum can be uncomfortable. A small dose of midazolam (2 mg) and alfentanil (250–500 μg) just before beginning the block procedure is usually adequate to decrease the discomfort. Excessive sedation should be avoided because positioning becomes difficult when patients cannot keep their balance in a sitting position. The first sign of successful blockade is the loss of pinprick sensation at the dermatomal distribution of the nerve being blocked. The higher the concentration and volume of local anesthetic used, the faster the onset.
Complications and How to Avoid Them
Table 24-2 lists the complications of intercostal block and preventive techniques.
Table 24-2 Complications of Intercostal Block and Preventive Techniques
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