The paravertebral space is a wedge-shaped area on both sides of the vertebral column (Fig. 32.1). The boundaries of the space are: posteriorly, the superior costotransverse ligament; laterally, the posterior intercostal membrane; and anteriorly, the parietal pleura. At the base of the triangle (medially) is the posterolateral aspect of the vertebra, disc, and intervertebral foramen (Fig. 32.2). Contents of the paravertebral space include fatty tissue, intercostal vessels, spinal (intercostal) nerve, dorsal ramus, rami communicantes, and sympathetic chain (anteriorly). The paravertebral space is continuous medially with the epidural space and laterally with the intercostal space. The inferior limit of this space occurs at the origins of the psoas major muscle. The superior limit extends into the cervical region.

Figure 32.1 Cadaver structures illustrating anatomy relevant to the paravertebral block. 1: spinous process; 2: vertebral body; 3: transverse process; 4: paravertebral space; 5: spinal canal.

Figure 32.2 Anatomy of the paravertebral space.

Surface anatomy

The main landmarks for the paravertebral block are the spinous and transverse processes. Identification of the appropriate vertebral level for blockade is facilitated by knowledge of dermatomes and anatomic landmarks that suggest vertebral level (Fig. 32.3). The spinous process of C7 (vertebrae prominens) is prominent and does not move with neck flexion. The spine and inferior angle of the scapula lie at the T3 and T7 vertebral levels, respectively.

Figure 32.3 Landmarks for the paravertebral block. The needle insertion point is 2.5 cm lateral to the spinous process. Approximate vertebral levels can be obtained by determining the positioning of the spine and inferior angle of the scapula and the vertebrae prominens (C7).

Sonoanatomy

A linear array transducer is placed initially at a point 2.5 cm lateral to the tip of the spinous process in a vertical orientation, obtaining a sagittal paramedian view of the transverse processes (TP), superior costotransverse ligament (SCTL) and underlying pleura (Fig. 32.4). The transverse processes are seen as interrupted hyperechoic lines with loss of image beneath. The parietal pleura is identified as a bright structure running deep to the adjacent TPs and can be seen to slide with patient respirations. The superior costotransverse ligament, though less distinct, is seen as a collection of homogeneous linear echogenic bands alternating with echo-poor areas running from one TP to the next (Fig. 32.4).

Figure 32.4 Ultrasound anatomy of a paravertebral space. Two bright lines demonstrate contiguous transverse processes, with the paravertebral space found between the superior costotransverse ligament and the underlying parietal pleura. LT: lung; PP: parietal pleura; SCTL: superior costotransverse ligament; TP: transverse process.

Technique

Landmark-based approach

As for all regional anesthetic procedures, after checking that emergency equipment is complete and in working order, intravenous access, ECG, pulse oximetry, and blood pressure monitoring are established. Asepsis is observed.

The patient is placed in the sitting or lateral position, with the head in the flexed position and the back arched. Choose which dermatomes will be involved in the operative field. The spinous processes are palpated and marked with a skin marker. A point 2.5 cm lateral to the spinous processes is marked.

The needle insertion point is infiltrated with local anesthetic using a 25-G needle. An 18-G Tuohy needle is inserted perpendicular to the skin until contact is made with the transverse process (Fig. 32.5). This usually occurs 2–4 cm from the skin. The location of the transverse process is critical in the performance of this block. If this contact is not made, it is likely that the needle lies between the transverse processes. The needle should be withdrawn and redirected in a caudal or cephalic direction (Fig. 32.6). Once the transverse process is identified, the needle is withdrawn and redirected in a cephalic/caudad direction to ‘walk’ over/under the transverse process.

Figure 32.5 Paravertebral block technique. The epidural needle is inserted perpendicular to the skin until contact with the transverse process.

Figure 32.6 Paravertebral block technique. The needle is ‘walked’ over the transverse process and advanced until a loss of resistance is identified.

The paravertebral space is usually found 1–1.5 cm deep to the transverse process. It is imperative that the needle should not be advanced beyond this point because there is a risk of pleural puncture. A subtle ‘click’ or loss of resistance is usually felt as the needle passes through the costotransverse ligament.

Incremental injections of local anesthetic (5 mL) are made with repeated aspiration. For a single-injection multisegment block, the volume used should be 15–25 mL. While the onset of analgesia is within minutes after injection of local anesthetic, up to 20 min is typically required for surgical anesthesia.

Local anesthetic solution injected into the paravertebral space may remain localized, spread to the ipsilateral paravertebral spaces above and below the injection site (Fig. 32.7), pass laterally through the intercostal space (Fig. 32.8), or spread medially through the epidural space or across the vertebral bodies. Thermographic studies have demonstrated that 15 mL of bupivacaine 0.5% produces a somatic block of five dermatomes, and a sympathetic block over eight dermatomes. Little is known regarding the factors that influence spread.

Figure 32.7 Coronal T1-weighted MR image showing cephalad and caudad spread of 20 mL of contrast injected below transverse process of T10. 1; contrast spread; 2: psoas muscle.

Figure 32.8 Axial T1-weighted MR image showing spread of contrast laterally below the ninth rib. 1: aorta; 2: intracostal contrast spread; 3: ninth rib; 4: T9 transverse process.

Ultrasound-guided approach

Intravenous access, ECG, pulse oximetry and blood pressure monitoring are established. The block tray is set up as previously outlined. The ultrasound machine and block tray should be placed in positions which allow the operator to simultaneously scan the patient and take items from the block tray with minimal movement. This setup may take some forethought but is a worthwhile exercise, and will facilitate successful regional anesthesia. The operator stands on the side to be blocked, with the patient in the sitting position (Fig. 32.9). The relevant spinous processes are palpated and marked. A line is drawn 2.5 cm lateral to the spinous process. The needle insertion point is 2.5 cm lateral to the relevant spinous process.

Figure 32.9 Global view of block field for ultrasound-guided thoracic paravertebral block.

The skin is disinfected with antiseptic solution and draped. A sterile sheath (CIVCO Medical Instruments, Kalona, IA, USA) is applied over the ultrasound transducer with sterile ultrasound gel (Aquasonic, Parker Laboratories, Fairfield, NJ, USA). Another layer of sterile gel is placed between the sterile sheath and the skin. The posterior chest wall is scanned with a 6–13 MHz linear transducer. The ultrasound screen should be made to look like the scanning field. That is, the right side of the screen represents the cephalad side of the field. Adjustable ultrasound variables such as scanning mode, depth of field, and gain are optimized.

The transverse processes are generally found at a depth of 2–3 cm from the skin. A sagittal image of the posterior chest wall is obtained and the transverse processes, superior costotransverse ligament and parietal pleura identified (Fig. 32.4). The midpoint of the transducer is aligned midway between the two adjacent TPs, local anesthesia is infiltrated at its lower border and an 18-G Tuohy needle introduced in a needle-in-plane approach in a cephalad orientation (Fig. 32.10). The paravertebral space is entered midway between the two TPs, avoiding bony contact. The tip of the needle is advanced under direct vision to puncture the superior costotransverse ligament. Saline (3 mL) is then injected deep to the SCTL to demonstrate the position of the injectate. Following a negative aspiration test, 15–20 mL of local anesthetic agent is injected and visualized filling the paravertebral space (Fig. 32.11).