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