Truncal blocks include the paravertebral, intercostal, pectoral nerve, suprascapular, ilioinguinal, iliohypogastric nerve, and transversus abdominis plane blocks. The anatomy involved in these blocks and conventional and ultrasound-guided techniques are discussed. The intercostal, suprascapular, ilioinguinal, and iliohypogastric nerve blocks are used mostly in patients with chronic pain. The paravertebral, transversus abdominis plane, and pectoralis nerve blocks significantly advanced perioperative pain management. The use of ultrasound improved the safety of these techniques.
Keywordsanatomy, clinical applications, complications, conventional technique, dosing, truncal blocks, ultrasound-guided technique
Truncal blocks are commonly employed for perioperative and chronic pain management. In this chapter, we will describe paravertebral (PV), intercostal, and transversus abdominis plane (TAP) blocks. The interpleural block will not be reviewed since this block is rarely used today. Pectoral nerve blocks appear to be promising for perioperative and chronic pain control, and will be analyzed. Suprascapular, ilioinguinal, and iliohypogastric nerve blocks will also be discussed since they are used to relieve pain in the trunk. In our discussions, comments on efficacy of the blocks, especially in the perioperative setting, will be minimal, and focus will be placed on the performance of the block.
Regional anesthetic techniques involving truncal neural blockade have enjoyed a resurgence in recent years, particularly with the introduction of ultrasound guidance techniques. PV blocks, when compared to epidural analgesia for patients undergoing thoracotomy, demonstrated no difference in opioid consumption or pain scores at 4–8, 24, and 48 hours, with fewer side effects including pulmonary complications, hypotension, urinary retention, and nausea and vomiting. Rates of failed blocks and complication rates were lower as well.
The PV space is a wedge-shaped area adjacent to the vertebral column that contains the sympathetic chain, the dorsal and ventral (intercostal) roots of the spinal nerve, the white rami communicantes, as well as fatty tissue and intercostal vessels ( Fig. 83.1 ). The base of the wedge constitutes the medial border of the PV space and is formed by the vertebral body and the intervertebral disc where there is communication with the epidural space via the intervertebral foramen. The posterior border of the PV space is the superior costotransverse ligament, which extends laterally to become continuous with the aponeurosis of the internal intercostal muscle. This internal intercostal membrane runs between the ribs, whereas the superior costotransverse ligament runs from the inferior border of the transverse process (TP) above to the superior border of the rib tubercle below. As the wedge tapers off laterally, it is continuous with the intercostal space. Anterior and lateral to the PV space is the parietal pleura. Within the PV space, the spinal nerves themselves do not have a fascial sheath and are easily susceptible to local anesthetic blockade. However, there is the endothoracic fascia, which is the deep investing fascia of the thoracic cavity, within the PV space, which can affect the spread of injected solutions.
Conventional techniques have described a loss-of-resistance approach to reach the PV space. A small-gauge Tuohy needle is inserted 2.5 cm lateral to the superior edge of the spinous process perpendicular to all planes, and is advanced until contact is made with the TP. The needle is then withdrawn to the skin, redirected caudad or cephalad by 15 degrees and advanced deep to the superior costotransverse ligament at which point a loss of resistance is achieved. To avoid pleural puncture, the needle is advanced 1 cm (and no further than 1.5 cm) past the point at which the TP was contacted. It is best to avoid medial angulation of the needle to minimize the risk of local anesthetic injection into a dural sleeve. It is also prudent to avoid lateral angulation given that the PV space is narrower laterally, increasing the risk of pleural puncture.
Ultrasound Guidance Technique
The addition of ultrasound guidance has been used to facilitate the thoracic PV in determining needle insertion sites, depth to TP and pleura, and needle tip location. A linear, high-frequency probe can be used, and in some instances, a curvilinear probe may offer a better approach to the PV space. Several major ultrasound-guided approaches have been described.
One approach utilizes ultrasound primarily to identify the TP. Once the TP is contacted under ultrasound guidance, the conventional loss-of-resistance technique is utilized. To visualize the TP, the ultrasound probe is placed in a longitudinal parasagittal plane 2.5 cm from the midline. Generally, a 5- to 10-degree tilt laterally is needed to best visualize the TP, which appears as a concave hyperechoic structure approximately 1 cm wide with anechoic space deep to it. This is commonly referred to as a “thumbprint sign.” The parietal pleura can be visualized approximately 1 cm deep to the TP on either side as a sharp hyperechoic line ( Fig. 83.2 ). The distance to the TP is variable depending on the level that is being blocked and the patient’s body habitus. The TP is at its most superficial location at levels T3–T5, usually at a distance of 1.5–2.5 cm, and is located deeper at levels cephalad and caudad to this. Ultrasound imaging has been shown to correlate well with the distance to the TP and the PV space, and usually underestimates these distances by 0.3–0.7 mm due to skin compression by the scanning head. Initial contact with the TP can be made with a 22-gauge finder needle that can serve to infiltrate local anesthetic. Once the TP is contacted with the seeker needle, the depth is noted, and a Tuohy needle or blunt-bevel block needle is introduced. To minimize the risk of pleural puncture, it is useful to have a needle with centimeter markings and a closed needle-syringe system relative to atmospheric pressure. Using an out-of-plane needle approach and similar to the conventional technique, the TP process is contacted and then redirected caudad 1 cm (and no more than 1.5 cm) past the TP. Loss of resistance to saline is confirmed and local anesthetic injection is performed by an assistant with intermittent aspiration while maintaining ultrasound visualization. It is important to note that loss of resistance can be very subtle and does not invariably occur. With ultrasound, downward movement of the parietal pleura is visualized as confirmation of correct local anesthetic placement. If a Tuohy needle was used, a catheter may be placed while maintaining lateral or cephalad needle tip orientation. One should expect slight resistance while passing the catheter. If no resistance is encountered, it is possible that the needle tip is in the intrapleural space.
Another approach is a slight variation of the first and utilizes an in-plane or out-of-plane approach to the PV space. The probe is in the identical longitudinal parasagittal plane as described above and the PV space is approached directly without first contacting the TP process. In utilizing this approach, precise needle tip visualization is important. If the needle tip is difficult to visualize, local anesthetic or saline can be injected incrementally to track needle tip advancement by hydrodissection. Again, a “pop” may be felt when the posterior costotransverse ligament is traversed with a corresponding loss of resistance.
Still another approach, the TP is initially imaged with a similar longitudinal parasagittal view, and the probe is then rotated obliquely to allow for the best view of the posterior costotransverse ligament and the PV wedge. The needle is advanced carefully utilizing an in-plane needle approach ( Fig. 83.3 ).
In an excellent review with elegant illustrations, Krediet et al. discussed the different approaches to PV block. The ultrasound is either placed in transverse or parasagittal direction with the needle either in-plane or out-of-plane. The “lateral approach” is aimed close to the tip of the TP or inbetween the ribs while the “medial approach’’ is performed medial to the costotransverse joint. The anatomical landmarks of all the approaches are the same: TP, rib, and pleura. For the novice, the authors recommended a parasagittal position of the transducer 2 cm lateral to the midline. An in-plane approach may require a steep angle of needle insertion due to the small distance between the adjacent TPs. Therefore, sometimes an out-of-plane approach may be necessary. For skilled practitioners, an in-plane transverse technique is an option. The needle is passed using an in-plane lateral to medial approach with the needle tip passing through the internal intercostal membrane. The final injection point is typically at the junction of the intercostal and PV spaces immediately ventrolateral to the tip of the corresponding TP. This approach allows for excellent needle visualization because it is typically more lateral than the parasagittal approach, and thus more superficial. However, if this technique is performed using a more medial injection site, where the PV space is larger, there are the associated increased risks of epidural or intrathecal spread, which the practitioner must consider.
The presence of the endothoracic fascia within the PV space can affect spread of injected solutions, and therefore some authors have suggested nerve stimulation in addition to the loss of resistance technique. Nerve stimulation can allow for more accurate placement of local anesthetic within the PV space; that is, anterior to the endothoracic fascia. Additionally, by injecting in this anterior location within the PV space, better craniocaudal spread in the PV “gutter” may be achieved and the need for multiple level injections obviated. This technique has not been studied in conjunction with ultrasound use. Conversely, other experts have argued that needle readjustment within the PV space may lead to a higher incidence of intravascular injections and pneumothorax, and that multiple-level PV injections allow for true graduated dosing of local anesthetic, and result in a more reliable spread of injectate within the PV space.
A single injection of 15 mL can be expected to provide analgesia over 3–4.6 dermatomes in the thoracic region. Spread is initially at the level of injection and along the intercostal nerve, and progresses in the PV “gutter” to cover one dermatome above and two dermatomes below. Most studies have shown a preferential caudad spread of injectate. Analgesia typically ranges from 6 to 12 hours for a single injection. If a catheter is placed, infusion of ropivacaine 0.2%–0.5% at rates of 4–8 mL/h may be used. Blood levels are similar to those seen with an epidural catheter.
Pneumothorax is estimated to occur in up to 0.5% of patients, yet most are not clinically significant and can be managed conservatively. Contrary to popular belief, violation of the parietal pleura does not result in aspiration of air unless the visceral pleura is also punctured or atmospheric air has entered the thoracic cavity. Instead, most patients will present with a sudden irritating cough or sharp pain in the chest. If the parietal pleura is violated, the block can be converted to an intrapleural block. It is important to remember that loss of resistance is not a consistent sign of entry into the PV space, and it is in these patients that ultrasound guidance should be of particular value. Also of note, patients with previous thoracotomy may have adhesions in the PV space, making PV catheter placement difficult.
Life-threatening complications from PV blocks have occurred as a result of bolus dosing. A bolus dose can accidentally be injected into the intrathecal or epidural space, or into a blood vessel. Many authors have argued that it is bolus dosing with subsequent intrathecal or intravascular spread—and not pneumothorax—that is the greatest risk associated with this procedure. Unilateral epidural spread is known to occur in 70% of patients; however, the majority of injectate remains confined to the PV and intercostal spaces. Bilateral epidural spread can occur through the ipsilateral epidural space or the prevertebral space and is usually associated with bolus dosing or medial angulation of the needle. Vascular puncture has been reported to occur in up to 3.8% of patients. Thus, graduated dosing either through a catheter or multiple injection points is recommended. Placement of PV blocks in the anticoagulated patient remains controversial and should probably be avoided, given that the space is in direct communication with the epidural space and not compressible.
Intercostal Nerve Block
In patients with spinal anomalies, trauma, or previous spine surgery that have altered epidural or PV anatomy, intercostal blocks can be used to provide chest wall analgesia.
As nerves leave the PV space, they enter the intercostal space and lie between the innermost intercostal muscle and the pleura. Lateral to the PV muscles, the prominent angles of the ribs are palpable as the primary landmark for intercostal nerve block. At the angle of the rib, the nerve lies between the innermost intercostal muscle and the inner intercostal muscle. Also, at this location, the thickness of the rib is approximately 8 mm and the costal groove is known to be the widest. Classically, the intercostal nerves have been thought to lie caudad to the intercostal vein and artery, on the inferior portion of the rib. However, a cadaver study found that the intercostal nerve remained in a classic subcostal position only 17% of the time. It was shown to be in a midcostal location most frequently (73%), and it was supracostal in some cadavers (10%). The intercostal nerves are the primary rami of thoracic nerves T1–T11. Most of the T1 nerve fibers combine with C8 to form the lower trunk of the brachial plexus. Fibers from T2 and T3 form the intercostobrachial nerve that supplies the upper chest wall along with cervical fibers from the brachial plexus. Intercostal nerves T4–T11 supply the thoracoabdominal wall from the nipple line to below the umbilicus. The T12 nerve is actually a subcostal nerve that contributes branches to the iliohypogastric and ilioinguinal nerves.
The ideal patient position is prone, with a pillow under the abdomen and both upper extremities hanging over the sides of the table, which maximizes retraction of the scapulae away from the upper ribs. This allows for bilateral blockade and posterior access to the angles of the ribs to enhance safety and success of the procedure. The lateral decubitus position is also quite satisfactory for unilateral blockade after rib fractures and lateral thoracotomy, as well as for chest tube placement. The supine position may also be utilized for bilateral block at the level of the midaxillary line; however, the rib and intercostal space are narrower here.
Classic techniques have described locating the angle of the rib (∼8 cm lateral to the midline) and using a 22-gauge, short-bevel needle to walk off 3-mm deep to the lower costal margin, and repeating this at the desired levels. More recently, ultrasound-guided approaches have been proposed. Ultrasound imaging is used to identify the space between the internal and innermost intercostal muscles 8 cm lateral to the spinous process, and D5W or saline can be injected to confirm needle tip position in the fascial plane and anterior pleural displacement. In a case report by Ben-Ari et al. the intercostal space was identified as described above, followed by placement of 19-gauge, wire-bound catheters. The catheters were then advanced 7 cm to the PV space, achieving a spread of five dermatomes.
Dosing and Complications
A single-shot intercostal block can be expected to provide analgesia for only 6–8 hours. Perineural catheter placement can provide for longer-lasting analgesia, and as described above the catheter can be advanced into the PV space. Total spinal anesthesia by injection into a dural sleeve is a rare but dangerous complication. Local anesthesia toxicity as a result of bolus dosing may occur due to rapid uptake from the well-vascularized intercostal space. Also, pneumothorax and liver subcapsular hematoma formation are potential complications. Ultrasound guidance may aid in maintaining better needle tip control and minimizing the occurrence of these complications.
Pectoral Nerve Blocks
Pectoral nerve blocks, also known as Pecs blocks, are suited for perioperative pain control and management of chronic pain after breast surgery. The blocks were initially described by Blanco et al. It consists of the Pecs block type I and type II blocks. The type I block appears to be suited for breast expander surgery and prosthesis insertion, when the pectoralis minor muscle is mainly affected. The type II block is employed for mastectomy and axillary dissection since the long thoracic and thoracodorsal nerves are involved. Another block, the serratus fascial plane block, was described to block the thoracic intercostal nerves primarily and provide analgesia to the lateral part of the thorax.
The pectoralis major muscle inserts superiorly into the inferior clavicle, supero-laterally into the proximal humerus, and medially into the sternum. It extends down to the seventh rib. The pectoralis minor muscle inserts supero-laterally into the coracoid process of the scapula and infero-medially into the third, fourth, and fifth ribs. The innervation for the pectoralis major comes from C5 to T1. The lateral and medial pectoral nerves, which branch off the brachial plexus, innervate the pectoralis major. They course between the pectoralis major and minor muscles after branching from the brachial plexus.
The original technique of the Pecs type I block involves insertion of the needle into the fascial plane between the pectoralis major and minor muscles ( Fig. 83.4 ). The ultrasound probe is placed below the clavicle, similar to an infraclavicular nerve block. The pectoral branch of the thoraco-acromial artery is identified. As the lateral pectoral nerve is consistently located adjacent to the artery, 10 mL of local anesthetic (e.g., 0.25% bupivacaine) is injected in the area. A variation of the original approach involves placement of the ultrasound probe below the outer third of the clavicle, transverse to the axis of the body ( Fig. 83.5A ). As in the original approach, the pectoralis major and minor muscles, and the thoracic-acromial artery and cephalic vein are identified. The needle is inserted in-plane, from medial to lateral direction, until the tip is in the interpectoral plane. Advantages of this approach include decreased incidence of vascular and pleural puncture and easier identification of the lateral border of the pectoralis minor muscle.