Sympathetic Blockade


The sympathetic nervous system (SNS) belongs to the autonomic nervous system, which owes its name to the fact that it operates independently. This means that there is no need for consciousness or will for it to carry out its functions, so it can act when we sleep or are engaged in some other activity that requires all our attention. The SNS works along the parasympathetic system, also part of the autonomic nervous system, controlling heart rate, blood pressure, sweating (body temperature regulation) and the functioning of many organs.

Right hand with CRPS

An excessive action of the SNS can induce pain or sweating in an area of the body. The most common result of excessive SNS action is chronic pain, particularly after trauma. It will typically appear after gunshot wounds, crushings, and after injuries of the peripheral nerves in general, but it can also occur after surgery, especially if it requires a long period of inactivity.

Right hand with CRPS

Once the process has been triggered, CRPS unfolds. Complex regional pain syndrome (CRPS) causes atrophy and pain in the affected limb, but there are many medications that can be used to control it, especially anti-epileptics, such as clonazepam or carbamazepine, and more specific drugs such as pregabaline. Performing rehabilitation on the affected limb is also useful.

If medication and physiotherapy fail to control CRPS, an SNS block, which is intended to cut the vicious circle that causes pain, can be considered. First, a test will be carried out in which special drugs are injected intravenously. These drugs will temporarily block the action of the SNS, improving the blood flow to the arm or leg. In many cases, this test will result in a more or less lasting relief of pain.

Depending on the outcome (if there is pain relief and to what degree), the procedure can be repeated or another treatment can be used. When a good response is obtained, this test can be used as a treatment and repeated several times to achieve a satisfactory result. If this turns out not to be the case, implanting a peripheral nerve stimulator or a spinal cord posterior column neurostimulator, or even perfoming a sympathectomy, may be considered.

The SNS block is used mainly in:

  • Blood flow disorders in an arm or leg.
  • CRPS, which is an over-stimulation of the autonomic nervous system due to small traumas, wrist fractures, and others.
  • Some types of neuralgia.


First, the anaesthesiologist will insert a venous line to administer the drugs. An elastic bandage will be applied to empty the affected limb of blood so that the blood flow to that limb can then be temporarily blocked. An inflated pressure cuff is left so that the blood does not flow to the limb before it should and the drugs are injected by the intravenous needle that has been previously inserted. The injected medication can induce pain, so it is injected together with local anaesthetic.

The procedure takes about an hour and a half, and once the drugs have carried out their function, the pressure cuff is removed and blood flow to the limb is restored.


The possible complications of this procedure may appear when the pressure cuff is released and usually involve temporary fluctuations in blood pressure. These fluctuations have usually a short duration, but may sometimes persist one or two days. Dizziness and nausea may also be experienced.

In addition, there may be a stuffy nose and red eyes as well as a bad taste in the mouth.


Two weeks after the procedure we can start to assess the result, but often the positive effect on pain perception appears just after the procedure is finished.

Please keep a diary where you record each day how the recovery is going and bring it to the office. Usually, other complementary treatments, such as the insertion of a peripheral nerve stimulator or a spinal cord posterior column neurostimulator, or even a sympathectomy, are required.

Please keep a diary where you record each day how the recovery is happening and bring it to the out-patients. Usually requires other complementary treatments (implantation of a peripheral nerve stimulator, implantation of a stimulation of the posterior columns of the spinal cord, or even a sympathectomy).


  • An SNS block must NOT be performed during pregnancy.
  • You must report ALL medications that you are taking, for some may interact with those used in this procedure.

You should return home with family or friends and not alone. You must not drive.

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