A lumbar nerve block, also known as a lumbar sympathetic block, is a treatment commonly used for pain that results from cancer, spinal problems, neurological disorders and shingles, or herpes zoster affecting the lower extremities. Depending on the condition and the physician, a lumbar nerve block can be done as an outpatient or inpatient procedure and may or may not require the use of sedation. While the patient is lying on his stomach, local anesthesia is used to numb the lower back area. Small gradual amounts of long acting local anesthetic are then injected into the nerve until symptom relief is achieved.

Following a lumbar nerve block, you may experience pain at the sites of the injections. In addition, according to the Pain Clinic website, a small number of patients experience genitofemoral neuralgia, which is pain that radiates into the groin area. It is believed that this side effect is a result of temporary bruising of the nerve as the needle passes by on it's way to the spine. Most individuals with this side effect will recover within six weeks, and the pain from the bruising can be relieved by prescription medication for nerve pain. Several other kinds of pain can occur as a side effect of a lumber nerve block including neuropathic pain, which results from injury to a nerve, and dull cramping, known as sympathalgia, which is usually temporary.

Following a lumbar nerve block, patients may experience minor bleeding at the site of injections. Additionally if, during the procedure, the needle accidentally injures the veins that lead to the heart, internal bleeding may occur and can require medical attention. Occasionally, a hematoma, or pooling of blood, in or around the injection site may occur and if large enough, will require medical attention. Any bleeding will likely be identified through radiological imaging that is performed during the procedure.

Aside from pain due to injury to nerves, a lumbar nerve block can also cause other neurological side effects including a headache, which results from loss of spinal fluid during the injection. This side effect usually subsides in a day or two with rest. A lumbar nerve block can also cause low blood pressure if a nerve that creates the impulse that controls blood pressure is injured. Men who have a bilateral nerve block are also at risk of impotence due to nerve damage; however, this rarely occurs.

Paraplegia, or paralysis of the lower limbs, is a rare side effect of lumbar nerve blocks caused by the accidental injection of the pain reliever into a major artery. The arteries run through the body and the medication will make it's way down to the legs, temporarily paralyzing them. In very rare circumstances, this condition can be permanent.