The thoracic sympathetic ganglia lie just lateral to the vertebral bodies and anterior to the spinal nerve roots, but this block is generally not used because of a significant risk of pneumothorax.
Splanchnic Nerve Block
Three groups of splanchnic nerves (greater, lesser, and least) arise from the lower seven thoracic sym-pathetic ganglia on each side and descend alongside the vertebral bodies to communicate with the celiac ganglia. Although similar to celiac plexus block, the splanchnic nerve block may be preferred because it is less likely to block the lumbar sympathetic chain and because it requires less anesthetic.
The needle is inserted 6–7 cm from the mid-line at the lower end of the T11 spinous process, and advanced under fluoroscopic guidance to the anterolateral surface of T12. Ten milliliters of local anesthetic is injected on each side. The needle should maintain contact with the vertebral body at all times to avoid a pneumothorax. Other complications may include hypotension and possible injury to the azy-gos vein on the right or to the hemiazygos vein and the thoracic duct on the left.
If a patient’s pain lessens after a splanch-nic nerve block, the procedure may be repeated to ensure that this result was not due to placebo effect. In addition, if the patient obtained pain relief from the initial block, he or she may subse-quently benefit from radiofrequency ablation of the splanchnic nerves at T11 and T12, with potentially longer duration of analgesia. Performing the proce-dure on one side initially, and then the other side on a subsequent day, is advised due to the risk of pneumothorax.