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Thoracic Paravertebral Nerve Block
This technique may be used to block the upper tho-racic segments, because the scapula interferes with the intercostal technique at these levels. Unlike an intercostal nerve block, a thoracic paravertebral nerve block anesthetizes both the dorsal and ven-tral rami of spinal nerves. It is therefore useful in patients with pain originating from the thoracic spine, thoracic cage, or abdominal wall, including compression fractures, proximal rib fractures, and acute herpes zoster. This block is also frequently uti-lized for intraoperative anesthesia and for postop-erative pain management in breast surgery.
Each thoracic nerve root exits from the spinal canal just inferior to the transverse process of its corre-sponding spinal segment.
This block may be performed with the patient prone, lateral, or seated position. A 5- to 8-cm 22-gauge spi-nal needle with an adjustable marker (bead or rubber stopper) is used. With the classic technique, the nee-dle is inserted 4–5 cm lateral to the midline at the spi-nous process of the level above. The needle is directed anteriorly and medially using a 45° angle with the mid-sagittal plane, and advanced until it contacts the transverse process of the desired level. The needle is then partially withdrawn and redirected to pass just under the transverse process. The adjustable marker on the needle is used to mark the depth of the spinous process; when the needle is subsequently withdrawn and redirected, it should not be advanced more than 2 cm beyond this mark. An alternative technique that may decrease the risk of pneumothorax uses a more medial insertion point and a loss-of-resistance tech-nique very similar to epidural anesthesia. The needle is inserted in a sagittal plane 1.5 cm lateral to the midline at the level of the spinous process above and advanced until it contacts the lateral edge of the lam-ina of the level to be blocked. It is then withdrawn to a subcutaneous position and reinserted 0.5 cm more laterally but still in a sagittal plane. As the needle is advanced, it engages the superior costotransverse ligament, just lateral to the lamina and inferior to the transverse process. The correct position may be identified by loss of resistance to injection of saline
when the needle penetrates the costotransverse liga-ment. Ultrasound guidance is helpful in performing this block .
The most common complication of paravertebral block is pneumothorax; accidental intrathecal, epidural, and intravascular injections may also occur. Sympathetic blockade and hypotension may be obtained if multi-ple segments are blocked or a large volume is injected at one level. A chest radiograph is mandatory if the patient exhibits signs or symptoms of pneumothorax.
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