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Intravenous guanethidine block

If you are considering having a thoracic epidural or have a procedure planned, it is important to know all you can about it. This includes:


  • why you need this procedure

  • what it will be like

  • how it will affect you

  • what risks are involved

  • any alternatives.


The information here is a guide to common medical practice. Each hospital and doctor will have slightly different ways of doing things, so you should follow their guidance where it is different from the information given here. Because all patients, conditions and treatments vary it cannot cover everything. Use this information when making your treatment choices with your doctors. You should mention any worries you have. Remember that you can ask for more information at any time.


What is the problem?

You have pain in an area of your body. It is usually a one-sided pain affecting one limb but it can be symmetrical, meaning it affects both sides. The pain involves the sympathetic nerves in this area. The sympathetic nerves control the things we do not need to think about, such as digestion, blood pressure and heart rate. This group of nerves do not normally send pain messages but they become ‘switched-on’ in certain painful states. We do not know why this happens, but have learnt to recognise the times when it does.


Pain from the sympathetic nerves does not respond to the usual painkillers that we may use for simple pain, like a headache. Neither does it respond to stronger painkillers that we might use for a broken bone. Sympathetic pain seems to be there all the time, sometimes getting worse and sometimes easing off. The pain may be affected by heat or cold and therefore change with the weather.


If the pain affects an arm or leg, the skin of the limb may appear pale or even mottled. There may be loss of hairs and the skin may take on a smooth, featureless appearance. Unfortunately, there is no exact test to confirm the diagnosis. The doctor recognises a pattern by the appearance of the skin and in the description of the pain, which is often sharp, stabbing or shooting.


What is an intravenous guanethidine block?

An intravenous guanethidine (IVG) block is an injection into a limb that is painful due to the activity of the sympathetic nerves.


By injecting local anaesthetic and a special drug called guanethidine into the affected limb the sympathetic nerves can be blocked. The pain messages sent by the nerves decrease and the pain is reduced.

Intravenous guanethidine block

What is guanethidine?

Guanethidine is a drug that blocks the ends of the sympathetic nerves. These nerves are thought to be responsible for some of the pain that you are feeling. When injected, the drug temporarily blocks the nerves. This means that the nerves are unable to send pain messages to your brain.


Guanethidine must be injected into a vein, on the painful limb. To make best use of guanethidine’s effect, it is kept inside the painful limb by inflating a pressure cuff, called a tourniquet, around that limb. If you have a painful lower leg, the cuff will be around your thigh. Likewise, if your hand or forearm is painful, then the cuff will be around your upper arm. This keeps the drug where it needs to act and prevents it spreading to the rest of the body. The cuff will stay up for about 20 – 30 minutes.


Guanethidine is very short acting. It is rapidly broken down and made inactive by the body over a period of hours.


The drug blocks all sympathetic nerves in the body to some degree. When the cuff is released and the drug goes into your circulation, your blood pressure may fall a little and your heart rate may increase. These are short lasting effects and you will return to normal within 30 minutes. To avoid dizziness at this time, you should remain lying flat.


What has gone wrong?

The sympathetic nerves in an area of your body have started sending pain messages. It is not at all clear why this happens. It is known that by blocking the activity of the sympathetic nerves the pain can be reduced.


The aims

The aim of the procedure is to reduce the signals sent by the sympathetic nerves and therefore reduce your pain.


The benefits

Your pain should be reduced and you should be able to move around more easily. If successful, this treatment can avoid the need for surgery.


Are there any alternatives?

By the time you consider a guanethidine block you should have already tried other more simple treatments. These include rest, painkilling and anti-inflammatory tablets, and physiotherapy with exercise.


You may have also tried a transcutaneous electrical nerve stimulation (TENS) machine for the pain. This works by sending soothing pulses across the surface of the skin and along the nerve fibres. The pulses prevent pain signals reaching the brain. They also stimulate your body to produce higher levels of its own natural painkillers, called endorphins.


What if you do nothing?

If you do nothing there are several things that may happen:


  • With time and rest your pain may settle on its own

  • Your pain and difficulty in performing daily activities may remain the same

  • Your pain may increase and spread

  • Your posture may get worse, making activities more difficult. The pain may even affect your sleep


Who should have it done?

The following groups of patients should have the procedure done:


  • Patients with pain in the area covered by a recognised group of sympathetic nerves, where the pain has failed to respond to standard treatments

  • Patients with limb pain in an arm or leg, with symptoms suggesting that the sympathetic nerves are involved.


Who should not have it done?

Each patient has the final decision on whether to proceed or not. If you are unhappy about the procedure for any reason you should not continue.


There are specific medical situations when an intravenous guanethidine block should not be done and they are as follows:


  • Patients who have severe heart disease, such as a previous heart attack

  • Patients who have an irregular heartbeat

  • Patients who have an implanted pacemaker

  • Patients who have low blood pressure, for any reason

  • Patients who have an allergy to guanethidine


These situations do not definitely prevent the procedure from taking place. You and your doctor should consider them seriously and carefully before agreeing to go ahead with the procedure.


Author: Dr Sean White FRCA. Consultant in pain and anaesthesia.

© Dumas Ltd 2006

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