Sympathetic Nerve Blocks

What is it?

The sympathetic nervous system is part of the autonomic (involuntary) nervous system. It regulates the width of blood vessels, sweating and the workings of the internal organs. Its nerve cells are arranged in chains and networks (plexuses) in front of and beside the spine. Some pain signals from the internal organs travel along these networks, and in certain chronic pain conditions the sympathetic system is thought to help keep the pain going.

A sympathetic nerve block places local anaesthetic, and sometimes other medicines, next to these nerve networks under image guidance. A block can be used for diagnosis, treatment or both. For cancer pain, switching off the nerve network for longer with a chemical agent or radiofrequency (neurolysis) is also an option.

When is it considered?

The main sympathetic blocks and their uses are:

• Stellate ganglion block: performed on a nerve cluster at the front and side of the neck. It may be considered for complex regional pain syndrome affecting the arm, and for selected types of headache and facial pain, such as shingles or post-shingles pain affecting the face.
• Lumbar sympathetic block: performed on the sympathetic chain in the lower back; used for complex regional pain syndrome in the leg and for pain related to poor circulation.
• Coeliac plexus and splanchnic nerve blocks: target pain from the upper abdominal organs, particularly pain from upper abdominal cancers such as pancreatic cancer.
• Superior hypogastric plexus and ganglion impar blocks: used for pain from the pelvic organs and the perineum, and for persistent tailbone pain.

These blocks are planned alongside medication and rehabilitation in the treatment of neuropathic pain, cancer pain and abdominal and pelvic pain.

The strength of the evidence depends on the use. In pancreatic cancer pain, a coeliac plexus block has been reported to reduce pain to some extent and to help lower the side effects of opioid painkillers. For complex regional pain syndrome, high-quality studies showing a benefit from sympathetic blocks are limited, so the block is used to help with physiotherapy and the response is monitored closely.

How does it work?

Local anaesthetic temporarily dampens the pain signals carried along the sympathetic network and any overactivity of the sympathetic system. After a block aimed at an arm or leg, warmth and a change in colour in that limb are signs that the block has worked.

A diagnostic block helps show whether the pain is linked to the sympathetic system. If the effect lasts longer than the medicine itself, several blocks may be repeated alongside a rehabilitation programme. In cancer pain, neurolysis can switch off the nerve network for longer; this option is considered according to the response to an earlier diagnostic block.

Before the procedure

The location and nature of your pain and your previous treatments are reviewed, along with any imaging. For people with cancer, the decision is made together with the oncology team. You and your doctor will plan how to manage any blood thinners.

Before an abdominal block, you may be asked to fast, and fluids may be given through a drip to help prevent a drop in blood pressure. Let the team know about any possibility of pregnancy, allergies or a fever. The aim of the procedure, possible risks and the alternatives are explained before you give your consent.

What happens during the procedure?

Your position depends on the type of block: you lie on your back for a stellate ganglion block and usually face down for lumbar sympathetic and coeliac plexus blocks. Your blood pressure, pulse and oxygen level are monitored throughout. Once the needle is in position under imaging, contrast dye is injected to check that the medicine will spread to the right area and that the needle is not in a blood vessel.

For blocks aimed at an arm or leg, the temperature of the limb may be measured during and after the procedure. Depending on the type of block, the procedure usually takes twenty to forty-five minutes.

After the procedure

Your blood pressure, pulse and the temperature of the affected limb are monitored for a while afterwards. After an abdominal block you may feel dizzy when standing up, so get up slowly for the first few hours. Diarrhoea lasting a few days can occur.

After a stellate ganglion block, a drooping eyelid, hoarse voice and difficulty swallowing may last a few hours; wait until these have worn off before eating or drinking. Tell the team straight away if you develop breathlessness, severe pain, a fever or weakness in the legs.

When might you notice results?

The local anaesthetic usually starts working within minutes. How long the relief lasts depends on the person and the type of block: for some people it lasts hours, for others days or weeks. After neurolysis for cancer pain, the effect usually lasts longer but may fade over time.

Results vary from person to person. If a block does not help enough, other interventional options such as radiofrequency treatment may be considered, or, for cancer pain, an epidural catheter or an intrathecal port. To discuss which approach suits you, you can request a consultation.