Intercostal Nerve Block

The intercostal nerves are the continuations of the ventral ramus of the thoracic spinal nerves. To perform an effective ICB, the block should be performed proximal to the mid-axillary line, where the lateral cutaneous branch takes off. ICBs can be performed using landmarks, a nerve stimulator, or under ultrasound guidance. Evidence supports the effectiveness of ICBs for chest tube placement, rib fractures, and procedures of the breast and chest wall. Limitations of ICBs include the need to perform blocks at multiple levels (each level of fractured rib) and their association with a shorter duration of action, compared to other chest wall fascial plane blocks such as pectoralis (PECS) II block and serratus anterior plane block (SAP). This is mainly related to a high rate of absorption of local anesthetic within the intercostal space. These considerations make ICBs a less favorable option, as with each injection, there is a potential risk of complications, such as neurovascular injury and pneumothorax. The risk of local anesthetic systemic toxicity (LAST) may also be increased with multiple intercostal injections related to the highly vascularized bundle located underneath each rib, resulting in a high rate of absorption.

Pectoralis and Serratus Anterior Plane Blocks

PECS and SAP blocks belong to the group of newly developed chest wall fascial plane blocks. A PECS I block refers to the injection of 10–20 mL of dilute local anesthetics between the pectoralis major and the pectoralis minor muscles. This interpectoral injection targets the medial (C8–T1) and lateral pectoral nerves (C5–C7), which, respectively, originate from the medial and lateral cords of the brachial plexus. The PECS II block consists of the same interpectoral injection (PECS I), with an additional injection between the pectoralis minor and the serratus anterior muscle (SAM). The deeper subpectoral injection blocks the intercostal nerves, long thoracic nerve, and thoracodorsal nerve. The PECS II injection is traditionally performed at the level of the fourth rib on the anterior axillary line. Indications for PECS I and II blocks include breast surgery such as lumpectomy, mastectomy, breast expander insertion, and radical mastectomy with axillary lymph node dissection. In addition, PECS II can also be used to provide analgesia on the medial side of the arm for upper extremity procedures such as elbow surgery or arterial–venous fistula placement.

At the axillary fossa, the intercostobrachial nerve, lateral cutaneous branches of the intercostal nerves (T3–T9), long thoracic nerve, and thoracodorsal nerve are located in a compartment between the serratus anterior and the latissimus dorsi muscles, and between the posterior and mid-axillary lines. The SAP block is therefore performed at around the fourth to fifth rib, with local anesthetics injected either superficial to the SAM (see Figure 11b.1, right arrow) and deep to the latissimus dorsi muscle or deep to the SAM and superficial to the rib (see Figure 11b.1, left arrow), though the former technique might be associated with more effective analgesia.

Figure 11b.1 Ultrasound-guided serratus anterior plane block. Arrow on the right pointing at the injection site between the latissimus dorsi muscle and the serratus anterior plane muscle, and arrow on the left pointing at the injection site between the serratus anterior plane muscle and the fifth rib.

Advantages of PECS blocks are that they can be used as alternatives to classic postoperative pain control modalities in the chest, such as thoracic epidural and thoracic paravertebral blocks (TPVBs), by providing somatic pain control and with the potential for fewer complications such as hypotension and urinary retention. The analgesic effects of PECS and SAP blocks are well supported by the literature, though it may be limited to the anterior two-thirds of the chest wall.

These blocks can be done with the patient supine and therefore can be performed in patients with polytrauma and those on total spine precautions or in pelvic traction who cannot be turned lateral or sat up, such as when needed for placement of thoracic epidurals or paravertebrals. In addition, these blocks are relatively superficial in location and easy and safe to perform under ultrasound guidance with a linear ultrasound transducer, and have fewer stringent restrictions on the coagulation status. Potential risks of PECS and SAP blocks include injury to the thoracodorsal and long thoracic nerves, vascular injuries, LAST, and pneumothorax. The novel chest wall blocks share similar analgesic benefits of thoracic epidural and TPVBs and can be used in unilateral or bilateral surgery for upper thoracic procedures in the format of a single injection or a continuous catheter.

Thoracic Paravertebral Block

The TPVB is a truncal plane block with a goal of analgesia/anesthesia of the left or right hemithorax. The technique requires the deposition of local anesthesia in the paravertebral space – immediately adjacent to the path of spinal nerves emerging from the intervertebral foramina. The block can be performed for surgical anesthesia but is most often relied upon as a source of postsurgical or trauma analgesia. This block can be performed with a variety of techniques, but ultrasound-guided techniques have led to a resurgence of this block.

The thoracic paravertebral space is an anatomical wedge-shaped region that lies immediately adjacent to the sides of the vertebral column. This space is bounded medially by the intervertebral disc and the intervertebral neurovascular foramen, the base by the body of the vertebrae, and anteriorly by the pleura. The posterior wall is formed by the costotransverse ligament, a fenestrated ligament complex that provides a window to access the space. The apex of the space is formed by the lower border of the transverse process and the confluence of fascia from surrounding structures in the region. The contents of the space are loose fatty connective tissue and the spinal nerve, dorsal ramus, sympathetic chain, rami communicantes, and intercostal vessels.

TPVBs are most commonly performed under ultrasound guidance with an in-plane approach. The ultrasonographic landmarking relies primarily on the image acquisition of the transverse process of the desired dermatomal level. A linear high-frequency probe (10–12 MHz) is placed over the transverse process in the axial plane. An image of the “squared-off” hyperechoic transverse process, costotransverse ligament complex, and moving pleura is acquired. The target space lies deep to the ligament complex and superficial to the pleura. The needle is advanced adjacent to the transverse process, through the ligament complex, and adjacent to the pleura. Local anesthetic deposition in the paravertebral space results in visible caudal and cephalad spread, and the anterior bulging of the parietal pleura. The cephalad and caudal spread of local anesthesia provides multilevel dermatomal spread.

Erector Spinae Plane Block

The thoracic erector spinae plane block (ESPB) is a relatively new truncal plane block that also provides analgesia to the left or right hemithorax. In a fashion distinct from, but not dissimilar to, the TPVB, this block anesthetizes the spinal nerve roots as they traverse the interverterbral foramina. The exact mechanism of this block is unclear and is likely to require ingress of local anesthesia across the costotransverse ligament complex. It is an ultrasound-guided technique that provides analgesia for procedures or pain involving the hemithorax.

The erector spinae muscle complex is formed from a trio of long, vertical cephalocaudal muscles: the spinalis, longissimus thoracis, and iliocostalis muscles. There is a space deep to these muscles, and superficial to the transverse process and costotransverse ligament complex. It is believed that the effect of ESPBs is through the movement of local anesthetic from this plane into the deeper paravertebral and epidural spaces, and laterally into the intercostal spaces. The costotransverse ligament complex is fenestrated, and thus may allow the spread of local anesthetic into these deeper spaces, resulting in anesthesia of the sympathetic nerve roots, as well as the dorsal and ventral rami. Diffusion laterally allows anesthesia of the somatic (intercostal) nerve. However, spread of local anesthetic has not been consistently seen in cavaderic studies, leaving some question as to the exact mechanism of action.

Similar to the TPVB, the ESPB is performed most commonly with ultrasound guidance and an in-plane approach. A linear high-frequency (10–12 MHz) ultrasound probe in the axial plane is frequently used. The probe is placed over the transverse process that corresponds to the desired level of blockade. The transverse process image is acquired approximately 3 cm lateral to the midline spinous processes, and is distinguished from the rounded ribs and flat, faint lines of the thoracic laminae (which are further lateral and medial, respectively) by its “squared-off” appearance. Deep to these structures is the hyperechoic and moving parietal pleura. A needle is advanced in plane directly at the transverse process. The needle is stopped just short of the transverse process (and many practitioners will strike the transverse process before withdrawing slightly). Local anesthesia deposition at this location results in an expansion of the plane deep to the fascia, lifting it off the transverse process and costotransverse ligament. Local anesthesia is seen to spread cephalad and caudal from this deposition, and much like the TPVB, spread in the plane is variable, resulting in a variable dermatomal distribution.