Peripheral Nerve Blocks of the Trunk: Paravertebral Block

Paravertebral Block

Paravertebral blocks provide surgical anesthesia or postoperative analgesia for procedures involving the thoracic or abdominal wall, mastectomy, ingui-nal or abdominal hernia repair, and more invasive unilateral procedures such as open nephrectomy. Paravertebral blocks usually require individual injections delivered at the various vertebral levels that correspond to the area of body wall to be anes-thetized. For example, a simple mastectomy would require blocks at levels T3–6; for axillary node dis-section, additional injections should be made from C7 through T2. For inguinal hernia repair, blocks should be performed at T10 through L2. Ventral hernias require bilateral injections corresponding to the level of the surgical site. The major com-plication of thoracic injections is pneumothorax, whereas retroperitoneal structures may be at risk with lumbar-level injections. Hypotension sec-ondary to sympathectomy can be observed with multilevel thoracic blocks. Unlike the intercostal approach, long-acting local anesthetic will have a nearly 24-hour duration, and perineural catheterinsertion is a viable option (although local anes-thetic spread from a single catheter to multiple lev-els is variable).

Each spinal nerve emerges from the interverte-bral foramina and divides into two rami: a larger anterior ramus, which innervates the muscles and skin over the anterolateral body wall and limbs, and a smaller posterior ramus, which reflects posteriorly and innervates the skin and muscles of the backand neck (Figure 46–62). The thoracic para-vertebral space is defined posteriorly by thesuperior costotransverse ligament, anterolaterally by the parietal pleura, medially by the vertebrae and the intervertebral foramina, and inferiorly and superi-orly by the heads of the ribs.

With the patient seated and vertebral column flexed, each spinous process is palpated, counting from the prominent C7 for thoracic blocks, and the iliac crests as a reference for lumbar levels. From the midpoint of the superior aspect of each spinous process, a point 2.5 cm laterally is measured and marked. In the thorax, the target nerve is located lat-eral to the spinous process above it, due to the steep

angulation of thoracic spinous processes (eg, the T4 nerve root is located lateral to the spinous process of T3).

A. Traditional Technique

A pediatric Tuohy needle (20 gauge) is inserted at each point and advanced perpendicular to the skin (Figure 46–62). Upon contact with the transverse process, the needle is withdrawn slightly and redi-rected caudally an additional 1 cm (0.5 cm for lum-bar placement). A “pop” or loss of resistance may be felt as the needle passes through the costotransverse ligament. Some practitioners use a loss-of-resistance syringe to guide placement; others prefer use of a nerve stimulator with chest wall motion for the end point. Inject 5 mL of local anesthetic at each level. The difficulty with this technique is that the depth of the transverse process is simply estimated; thus the risk of pneumothorax is relatively high. Using ultrasound to gauge transverse process depth prior to needle insertion theoretically decreases the risk of pneumothorax.

B. Ultrasound

An ultrasound transducer with a curvilinear array is used, with the beam oriented in a parasagittal or transverse plane. The transverse process, head of the rib, costotransverse ligament, and pleura are iden-tified. The paravertebral space may be approached from a caudal-to-cephalad direction (parasagittal) or a lateral-to-medial direction (transverse). It is helpful to visualize the needle in-plane as it passes through the costotransverse ligament and observe a downward displacement of the pleura as local anes-thetic is injected. At each level 5 mL of local anes-thetic is injected.