Guanethidine block injections

What are guanethidine block injections?

A guanethidine block is an injection used to treat persistent pain in an arm or leg. Guanethidine is a drug that can block pain signals travelling along the sympathetic nerves in your limb, and it’s injected into a vein while a tourniquet keeps it from reaching the rest of your body.

What conditions does it treat?

Guanethidine blocks are used to treat pain conditions affecting one limb, most often Complex Regional Pain Syndrome (CRPS), also known as reflex sympathetic dystrophy, Sudek’s atrophy, causalgia or algodystrophy. Symptoms of CRPS can include severe burning pain, swelling, and changes in skin colour, temperature or sweating.

This treatment is especially used once other treatments haven’t worked. It has also been used successfully in children who have pain, blueness or a burning feeling in their leg.

What are the benefits of guanethidine block injections?

Guanethidine blocks can offer:

• pain relief when other treatments haven’t worked
• in one clinical study of 17 people with CRPS of the hand, complete pain relief and full return of normal function and movement, with no side effects observed
• relief that tends to last longer with each repeated injection, if the first is effective.

Are there different approaches?

Choice of medication

Guanethidine is usually combined with a local anaesthetic for the injection. Depending on your consultant’s assessment, a different drug called phentolamine may be used instead of guanethidine for the same type of block.

Number of sessions

Guanethidine blocks are rarely given as a single treatment. Your consultant may recommend a course of several injections, as pain relief often improves and lasts longer after each one.

What happens before the procedure?

You’ll usually be asked to take your regular medications as normal on the day, and bring a list of what you’re taking with you. If you have diabetes or take warfarin, you’ll be given specific individual advice. Sedation isn’t usually needed for this procedure, but you can discuss this with your consultant beforehand if you feel very anxious about it.

What happens during the procedure?

1. A small cannula (thin tube) is placed into a vein in the hand or foot of the affected limb, and a second cannula is placed in your other hand, in case you need treatment for side effects such as low blood pressure.
2. Your limb is raised for a few minutes to help empty the veins.
3. A tourniquet or pressure cuff is wrapped around your upper arm or thigh and inflated tightly, to keep the drug within the affected limb only.
4. Guanethidine and a local anaesthetic are injected through the cannula into the limb; your limb may feel numb and look blotchy or white, which is expected.
5. You rest for around 20 minutes while the drugs spread through the tissues of your limb.
6. The tourniquet is slowly deflated, and you may notice a warm, tingling feeling, or some pins and needles.

Throughout the procedure, your blood pressure and oxygen levels are monitored closely.

What does recovery look like?

In hospital

You’ll usually need to stay in hospital for around 1–2 hours after your injection, sometimes a little longer, while nursing staff monitor your blood pressure and heart rate. Your limb may look rosy, and feel numb or weak for a while; if you’ve had treatment in your leg, you may need help from staff when you first get up. A small dressing over the injection site can usually be removed after 24 hours.

At home

You’ll need to arrange for an adult to drive you home, as you won’t be able to drive for at least 24 hours, and to have someone with you for the rest of that day and overnight. If this isn’t possible, you may need to stay in hospital overnight instead.

The local anaesthetic wears off within a few hours, but the effect of the guanethidine on your sympathetic nerves can last from many hours to several days. It’s important to move your limb as much as you comfortably can to help prevent stiffness, though resting it can help if you notice pins and needles.

A follow-up session with a physiotherapist is often recommended, to help you build up exercises for the limb once the block has taken effect. If your first injection reduces your pain significantly, your consultant may suggest further sessions; how many you need varies, but relief often lasts longer after each one.

What are the risks and complications?

Guanethidine blocks are generally very safe, but there are some risks to be aware of:

• an allergic reaction to guanethidine
• a temporary drop in blood pressure, which is why your blood pressure is monitored closely throughout and a second cannula is placed in case treatment is needed
• feeling faint or blacking out if the tourniquet doesn’t work as intended
• discomfort or numbness from the pressure cuff, and pins and needles as the tourniquet is released, which are expected and usually settle on their own.

Guanethidine can also lower blood pressure more generally, particularly on standing or with exercise, and may occasionally cause sexual side effects or diarrhoea.