- Indications: breast surgery, analgesia after thoracotomy or in patients with rib fractures
- Landmarks: spinous process at the desired thoracic dermatomal level
- Needle insertion: 2.5 cm lateral to the midline
- Target: needle insertion 1 cm past the transverse process
- Local anesthetic: 5 mL per dermatomal level
Thoracic paravertebral block.
A thoracic paravertebral block is a technique where a bolus of local anesthetic is injected in the paravertebral space, in the vicinity of the thoracic spinal nerves following their emergence from the intervertebral foramen. The resulting ipsilateral somatic and sympathetic nerve blockade produces anesthesia or analgesia that is conceptually similar to a "unilateral" epidural anesthetic block. Higher or lower levels can be chosen to accomplish a unilateral, bandlike, segmental blockade at the desired levels without significant hemodynamic changes. For a trained regional anesthesia practitioner, this technique is simple to perform and time efficient; however, it is more challenging to teach because it requires stereotactic thinking and needle maneuvering. A certain "mechanical" mind or sense of geometry is necessary to master it. This block is used most commonly to provide anesthesia and analgesia in patients having mastectomy and cosmetic breast surgery, and to provide analgesia after thoracic surgery or in patients with rib fractures. A catheter can also be inserted for continuous infusion of local anesthetic.
The thoracic paravertebral space is a wedge-shaped area that lies on either side of the vertebral column (Figure 23-2). Its walls are formed by the parietal pleura anterolaterally; the vertebral body, intervertebral disk, and intervertebral foramen medially; and the superior costotransverse ligament posteriorly. After emerging from their respective intervertebral foramina, the thoracic nerve roots divide into dorsal and ventral rami. The dorsal ramus provides innervation to the skin and muscle of the paravertebral region; the ventral ramus continues laterally as the intercostal nerve. The ventral ramus also gives rise to the rami communicantes, which connect the intercostal nerve to the sympathetic chain. The thoracic paravertebral space is continuous with the intercostal space laterally, epidural space medially, and contralateral paravertebral space via the prevertebral fascia. In addition, local anesthetic can also spread longitudinally either cranially or caudally. The mechanism of action of a paravertebral blockade includes direct action of the local anesthetic on the spinal nerve, lateral extension along with the intercostal nerves and medial extension into the epidural space through the intervertebral foramina.
Anatomy of the thoracic spinal nerve (root) and innervation of the chest wall.
Thoracic paravertebral blockade results in ipsilateral anesthesia. The location of the resulting dermatomal distribution of anesthesia or analgesia is a function of the level blocked and the volume of local anesthetic injected (Figure 23-3).