A nerve block is a medical procedure used to manage chronic pain by temporarily interrupting signals traveling along a nerve pathway. A sympathetic nerve block targets a specific part of the nervous system to break the cycle of persistent pain, especially when the nervous system is sending faulty signals. The procedure chemically silences the nerves that may be inadvertently amplifying or maintaining pain sensations.
Understanding the Sympathetic Nervous System Target
The sympathetic nervous system (SNS) is part of the body’s autonomic nervous system, controlling involuntary functions such as heart rate and the “fight-or-flight” response. This system operates through ganglia, which are nerve bundles positioned close to the spine. Although the SNS primarily regulates blood flow and temperature, it can become involved in chronic pain transmission following injuries or diseases.
In chronic pain states, the SNS may start transmitting or amplifying pain signals, an abnormal activity sometimes called sympathetically maintained pain. The sympathetic nerve block is designed to interrupt this feedback loop at the ganglia.
The mechanism involves injecting a medication mixture directly into or near the targeted ganglion. This mixture typically contains a local anesthetic to temporarily numb the nerves, and sometimes a corticosteroid to reduce inflammation. This chemically silences the sympathetic chain, preventing the transmission of problematic pain signals.
Conditions Managed by a Nerve Block
Sympathetic nerve blocks are used to diagnose and treat chronic pain conditions where the SNS is suspected of maintaining the pain. The most common indication is Complex Regional Pain Syndrome (CRPS), formerly known as Reflex Sympathetic Dystrophy (RSD). CRPS is characterized by disproportionate pain, swelling, and changes in skin color or temperature, often triggered by trauma to a limb.
The block is also utilized for persistent vascular pain, including Raynaud syndrome or pain due to insufficient blood flow. Blocking the sympathetic nerves can widen blood vessels, improving circulation and reducing ischemic pain. Another indication is phantom limb pain, a persistent sensation of pain in an amputated limb.
Executing the Block Procedure
The sympathetic nerve block is performed as an outpatient procedure by a pain management specialist or anesthesiologist. Before starting, the patient’s vital signs are monitored, and an intravenous (IV) line may be placed to administer a mild sedative for comfort, though the patient remains awake. The specific location for the injection depends on the location of the patient’s pain.
For upper body pain, such as the arm or head, the injection targets the stellate ganglion in the neck. For lower body pain, affecting the leg or foot, the target is the lumbar sympathetic chain, located on either side of the lower spine. To ensure accuracy, the physician uses real-time imaging guidance, typically fluoroscopy (a form of X-ray) or ultrasound, to visualize the needle’s path.
Once the needle is confirmed to be in the precise location, a contrast dye may be injected to verify the medication will spread correctly around the nerve bundle. The local anesthetic and any other medication are then injected, and the needle is removed. The entire procedure is relatively quick, and the patient is moved to a recovery area for observation before discharge.
Post-Procedure Recovery and Safety
Immediately following the procedure, the patient is monitored for about an hour to ensure there are no adverse reactions. Patients often experience immediate, temporary pain relief as the local anesthetic takes effect. A common side effect is warmth, flushing, or redness in the affected limb, which indicates the block successfully increased blood flow.
If the stellate ganglion was targeted, temporary changes known as Horner’s Syndrome—such as a droopy eyelid, hoarse voice, or difficulty swallowing—are common and resolve within a few hours. Pain relief can last from a few hours to several weeks, and a series of blocks is often necessary for sustained therapeutic effect. If a steroid was included in the injection, the full benefit may not be felt until two to three days later.
While the procedure is generally safe, patients must arrange for someone to drive them home if sedated and avoid strenuous activity for the rest of the day. Patients should seek immediate medical attention for signs of infection, significant weakness in the limbs, or loss of bladder or bowel control.