• Anthony M-H. Ho, MD

       THORACIC PARAVERTEBRAL BLOCK

Thoracic paravertebral block (TPVB) is the technique of injecting local anesthetic alongside the thoracic vertebra close to where the spinal nerves emerge from the intervertebral foramen.^{1, 2} This produces unilateral, segmental, somatic, and sympathetic nerve blockade,³ which is effective for anesthesia and in treating acute and chronic pain of unilateral origin from the chest and abdomen.¹ Hugo Sellheim of Leipzig (1871–1936) is believed to have pioneered TPVB in 1905.^{1, 2} Kappis, in 1919, developed the technique of paravertebral injection, which is comparable to the one in present-day use. Although paravertebral block was fairly popular in the early 1900s, it seemed to have fallen into disfavor during the mid and later part of the century, the reason for which is not known. In 1979 Eason and Wyatt rekindled interest by describing a technique of paravertebral catheter placement.⁴ Our understanding of the safety and efficacy of TPVB has improved significantly in the last 25 years, and there has been a gradual renewal of interest in this technique. Currently it is used not only for analgesia but also for surgical anesthesia,^5–7 and its application has been extended to children.^8–10

Anatomy

The thoracic paravertebral space (TPVS) is a wedge-shaped space located on either side of the vertebral column (Figure 43–1). The parietal pleura forms the anterolateral boundary. The base is formed by the vertebral body, intervertebral disc, and the intervertebral foramen with its contents. The transverse process and the superior costotransverse ligament form the posterior boundary. Lying in between the parietal pleura anteriorly and the superior costotransverse ligament posteriorly is a fibroelastic structure, the endothoracic fascia, which is the deep fascia of the thorax (Figure 43–1 through 43–3).^1,11–15 Medially the endothoracic fascia is attached to the periosteum of the vertebral body. A layer of loose areolar connective tissue, the subserous fascia, lies between the parietal pleura and the endothoracic fascia. Therefore there are two potential fascial compartments in the TP VS: the anterior extrapleural paravertebral compartment and the posterior subendothoracic paravertebral compartment (see Figures 43–1 and 43–2). The TPVS contains adipose tissue within which lie the intercostal (spinal) nerve, the dorsal ramus, intercostal vessels, rami communicantes, and anteriorly the sympathetic chain. The spinal nerves are segmented into small bundles and lie freely in the adipose tissue of the TPVS, which make them accessible to local anesthetic solutions injected into the TPVS.¹⁶

Figure 43–1. Anatomy of the thoracic paravertebral space. SP, spinous process; TP, transverse process; VB, vertebral body. The blue shaded area represents the paravertebral space.

        The TPVS communicates with the epidural space medially^17,18 and with the intercostal space laterally. The TPVS on either side of the thoracic vertebra also communicate with each other through the epidural and prevertebral space.^1,12,15 The cranial extension of the TPVS is challenging to define and may significantly vary; however, we have observed direct paravertebral spread of radiopaque contrast medium from the thoracic to the cervical paravertebral space, indicating a direct anatomic continuity. The TPVS also communicates caudally through the medial and lateral arcuate ligaments with the retroperitoneal space behind the fascia transversalis, where the lumbar spinal nerves are located.^{13, 19–21}

Mechanism of Block & Distribution of Anesthesia

TPVB produces ipsilateral somatic and sympathetic nerve blockade (Figure 43–4) due to a direct effect of the local anesthetic on the somatic and sympathetic nerves in the TPVS, extension into the intercostal space laterally, and the epidural space medially. The overall contribution of epidural spread to the dermatomal distribution of anesthesia following a TPVB is not well defined. However, some degree of ipsilateral spread of local anesthetic toward the epidural space probably occurs in the majority of patients, resulting in a greater distribution of anesthesia than occurs with paravertebral spread alone.¹⁸ The dermatomal distribution of anesthesia following a single injection of a large volume (eg, injection of 15–25 mL of local anesthetic at one level) varies and is often unpredictable.^1,3,22 However, the injected solutions routinely spread both cephalad and caudad to the site of injection to some extent (Figure 43–5). Nevertheless, the multiple- injection technique, where small volumes (3–4 mL) of local anesthetic are injected at several contiguous thoracic levels, is preferable over single, large-volume injection. This is particularly important when reliable anesthesia over several ipsilateral thoracic dermatomes is desired, such as when TPVB is used for anesthesia during breast surgery.

Figure 43–2. The endothoracic fascia and its anatomic relation to the structures in the thoracic paravertebral space. Note the fascial compartments and the location of the neurovascular structures in relation to the endothoracic fascia.

Segmental contralateral anesthesia, adjacent to the site of injection, occurs in approximately 10% of patients after single-injection TPVB and may be due to epidural or prevertebral spread. Bilateral symmetrical anesthesia due to extensive epidural spread or unintentional intrathecal injection into a durai sleeve may occur, particularly when the needle is directed medially or when a larger volume of local anesthetic (>25 mL) is used. For this reason, during placement of TPVB, patients should be monitored using the same vigilance and methods as those employed for injection using the large-volume, single-injection epidural technique. The ipsilateral ilioinguinal and iliohypogastric nerves may also occasionally be involved after lower thoracic paravertebral injections. This is either due to epidural spread or extended subendothoracic fascial spread to the retroperitoneal space where the lumbar spinal nerves are located. The effect of gravity on the dermatomal spread of anesthesia after TPVB is unknown, but there may be a tendency for preferential pooling of injected solution toward the dependent levels.^3,23,24

Figure 43–3. Sagittal section through the thoracic paravertebral space showing a needle that has been advanced above the transverse process.

Figure 43–4. Segmental thoracic anesthesia achieved with paravertebral blocks.

Figure 43–5. Radiopaque contrast imaging shows spread of the injectate (3 mL) cephalad and caudad to the tip of the catheter placed in the paravertebral space.

Technique

It is preferable to perform TPVB with the patient in the sitting position because the surface anatomy is better visualized and patients are often more comfortable. However, when this is not possible or practical, TPVB can also be performed with the patient in the sitting, lateral, or prone position. The number and level of injections are selected according to the desired spread of local anesthesia. In this example, description of the TPVB for breast surgery is described. Surface landmarks are identified and marked with a skin marker before block placement (Figure 43–6). Skin markings are also made 2.5 cm lateral to the midline at the thoracic levels that are to be blocked. These markings indicate the needle insertion sites and should lie over the transverse process of the vertebra (Figure 43–7).

Figure 43–6. Surface landmarks for thoracic paravertebral blocks.

        A standard regional anesthesia tray is prepared, and strict asepsis should be maintained during block placement. A 22-gauge Tuohy- or Quincke-tip spinal needle is used for a single- or multiple-injection TPVB (Figure 43–8). If the needle does not have depth markings on its shaft, a depth guard (see Figure 43–8) is recommended. An epidural set is used if insertion of a catheter into the TPVS is planned. Multiple injections during TPVB are uncomfortable and require a proper premedication (eg, midazolam 2–3 mg plus fentanyl 50–100 meg) to ensure patient acceptance and comfort during the block placement.

Figure 43–7. Relationship between spinous and transverse processes.

Figure 43–8. Needles commonly used for a single- or multiple-injection thoracic paravertebral block. Note the depth guard that is attached to the Quincke-tip spinal needle (middle).

Figure 43–9. Special relationship between the spinous and transverse processes at the thoracic level. Due to the steep downward angulation of the spinous processes at the thoracic levels, the needle inserted at the level of the spinous process contacts the transverse process that belongs to the vertebra below it.

Loss-of-Resistance Technique

There are several different techniques of TPVB. The classical technique involves eliciting loss of resistance. The skin and underlying tissue is infiltrated with lidocaine 1%, and the block needle is inserted perpendicular to the skin in all planes to contact the transverse process of the vertebra. Note that due to the acute angulation of the thoracic spines in the midthoracic region, the transverse process that is contacted is the one from the lower vertebra (Figures 43–9 and 43–10).

Figure 43–10. Technique of “walking off” the transverse process. A: The needle is shown contacting the transverse process. B: The needle is shown walking off the superior aspect of the transverse process.

The depth at which the transverse process is contacted varies (3–4 cm) and depends on the build of the individual and the level at which the needle is inserted. The depth is deeper at the cervical and lumbar spine level and shallower at the thoracic levels. During needle insertion it is possible to miss the transverse process and inadvertently puncture the pleura. Therefore it is imperative to search and make contact with the transverse process before advancing the needle too deep and risking pleural puncture. To minimize this complication, the block needle should initially be inserted only to a maximum depth of 4 cm at the thoracic and 5 cm at the cervical and lumbar levels. If bone is not contacted it should be assumed that the needle is in between two adjacent transverse processes. The needle should be withdrawn to the subcutaneous tissue and reinserted with a cephalad or caudad direction to the same depth (4 cm) until bone is contacted. If bone is still not encountered, the needle is advanced a further centimeter and the above procedure repeated until the transverse process is identified. The needle is then walked above (these authors’ preference) or below the transverse process and gradually advanced until a loss of resistance is elicited as the needle traverses the superior costotransverse ligament into the TPVS (Figures 43–3 and 43–11). This usually occurs within 1 to 1.5 cm from the superior edge of the transverse process (see Figure 43–3). Although a subtle “pop” or “give” may be appreciated as the needle traverses the superior costotransverse ligament, this should not be entirely relied on. Instead, the depth of the needle placement should be guided by the initial bone contact (skin-transverse process plus 1 to

1.5 cm). Unlike localization of the epidural space, in which the loss of resistance is typically unequivocal, loss of resistance elicited during TPVB is very subtle and takes time to appreciate and master. The use of a glass syringe may facilitate recognition of the loss of resistance when this method is used.

Figure 43–11. Paravertebral block technique. The needle (1) is first advanced to contact the transverse process (4), then redirected cephalad (2) or caudad to walk off the transverse process and enter the paravertebral space. Other structures shown are spinous process (3) and the dispersion of the dye in the paravertebral space and intercostal sulcus (5).

Predetermined Distance Technique

TPVB can also be performed by advancing the needle by a fixed predetermined distance (1 cm) once the needle is walked off the transverse process, without eliciting loss of resistance (Figure 43–12).^5–7,23 Proponents of this technique have used it very successfully with low risk of pneumothorax. The use of a depth marker is recommended to avoid inadvertent pleural or pulmonary puncture.

Figure 43–12. Paraverterbral block—the image shows needle advancement at the predetermined level. The fingers of the advancing hand are preventing insertion of the needle too deep.

Clinical Pearls

Placement of Thoracic Paravertebral Catheter

If a continuous TPVB (CTPVB) is planned, a catheter is inserted through a Tuohy needle into the TPVS.^{4, 22} Unlike epidural catheterization, certain resistance is commonly encountered during insertion of the paravertebral catheter. This can be overcome by manipulating (rotating or angling) the needle or injecting 5–10 mL of saline to create a space before catheter insertion. An unusually seamless passage of catheter should arouse the suspicion of interpleural placement.

        Perhaps the safest and simplest method of placing a catheter into the TPVS is to place it under direct vision from within the open chest cavity.^{8, 25} Obviously, this requires an open thorax and is therefore done exclusively in patients undergoing a thoracotomy. This technique involves reflecting the parietal pleura from the posterior wound margin onto the vertebral bodies over several thoracic segments, thereby creating an extrapleural paravertebral pocket (Figure 43–13) into which a percutaneously inserted catheter is placed against the angles of the exposed ribs. The pleura is reapposed to the chest wall, and the thorax is closed. This method can be combined very effectively with a preinci- sional, single-shot, percutaneous thoracic paravertebral injection to provide perioperative analgesia during thoracic surgery.²⁶

Figure 43-13. A:Extrapleural paravertebral catheter placement under direct vision in an infant. Figure shows a curved artery forceps that has been inserted into the extrapleural paravertebral pocket that was created by reflecting the parietal pleura from the posterior wound margin onto the vertebral bodies over several thoracic dermatomes. B: Extrapleural paravertebral catheter placement under direct vision in an infant. The figure shows a Tuohy needle that has been inserted from the lower intercostal space into the thoracic paravertebral space, ie, the extrapleural paravertebral pocket previously created. A catheter is then inserted through the Tuohy needle and secured in place against the angles of the exposed ribs, after which the pleura is reapposed and the chest is closed.

Clinical Pearls

Related posts:

Regional Anesthesia in the Patient with Preexisting Neurologic Disease. The History of Local Anesthesia. Stimulating Catheters. Ultrasound-Assisted Nerve Blocks in Adults. Cutaneous Blocks for the Upper Extremity. Cervical Plexus Block.