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
