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Phentolamine test

If you are considering having a phentolamine test 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. This could be a limb, your chest or your face. It is usually unilateral, meaning it is a one-sided pain. The pain may involve 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 does not normally send pain messages, but they become ‘switched-on’ in certain conditions. 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 may change with the weather.


If the pain affects your arm or leg, the skin can be seen to go pale or even mottled. There may be hair loss and the skin may take on a smooth, featureless appearance. Unfortunately, there is no exact test to confirm the diagnosis, but a phentolamine test can give useful information. The doctor recognises a pattern in the description of the pain, which is often sharp, stabbing or shooting, and by the appearance of the skin.


What is a phentolamine test?

A phentolamine test is a drug test. A drip carrying the phentolamine is run into a vein (intravenous) for 20 minutes. It is used to tell whether the sympathetic nerves are carrying any of the pain that you feel. It is a simple test. If your pain is reduced while the drug is running into your body, this is a positive result. We then know that the sympathetic nerves are involved in your pain. This guides further treatment aimed at blocking the pain messages from the sympathetic nerves with local anaesthetic.

Phentolamine test

What is phentolamine?

Phentolamine is a drug that blocks the ends of the sympathetic nerves. By doing this it reduces the ability of these nerves to send pain signals. The drug is very short acting and is rapidly broken down and made inactive by the body.


As the drug blocks all the sympathetic nerves to some degree, your blood pressure may fall and your heart rate may increase. Once this happens, we know there is enough phentolamine in the body to have its effect for the test. In controlled conditions the fall in your blood pressure is not dangerous.


What has gone wrong?

The sympathetic nerves control the things we do not need to think about, such as sweating, blood pressure and heart rate. This group of nerves does not normally send pain messages but your sympathetic nerves appear to have started to. It is not at all clear why this happens. It is known that we can reduce the pain by blocking the activity of the sympathetic nerves in these situations.


The aims

The aim of the procedure is to reduce the signals sent by the sympathetic nerves and hence reduce the pain. If this happens during the test we know that the sympathetic nerves are involved in your pain. This directs further treatment. This may be to take some tablets to reduce the pain signals from the sympathetic nerves. Alternatively, you may be suitable for some injections of local anaesthetic to the sympathetic nerves.


The benefits

Your pain should be reduced during the treatment. The result of the test will be used to direct further treatment. If further treatment is successful it can avoid the need for tablet medications.  


Are there any alternatives?

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


You may have also tried a transcutaneous electrical nerve stimulation (TENS) machine for your pain. This works by sending soothing pulses across the surface of the skin and along the nerve fibres. The pulses prevent pain signals from 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 the pain may settle on its own

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

  • The pain may increase and spread

  • The pain may cause your posture to get worse, making daily activities and even sleeping more difficult


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, that has failed to respond to standard treatments

  • Patients with pain in an area, 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.


Phentolamine blocks all the sympathetic nerves to some degree, so your blood pressure may fall and your heart rate may increase. Therefore a phentolamine test should not be done in the following situations:


  • When a patient has severe heart disease, such as a previous heart attack

  • When a patient has an irregular heartbeat

  • When a patient has an implanted pacemaker

  • When a patient has low blood pressure, for whatever reason


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

© Dumas Ltd 2006

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