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Epidurals for surgery and pain relief

Published by Bupa's health information team, May 2008.

This factsheet is for people who are planning to have an epidural to provide anaesthesia for surgery, and/or to control pain afterwards, or who would like information about it.

Local anaesthetic or pain relief medicine is injected into the epidural space that surrounds the spinal cord.

Epidurals are also used for the treatment of chronic back pain and sciatica (shooting pain down one or both legs) and in childbirth, but these won't be discussed here.

Your care will be adapted to meet your individual needs and may differ from what is described here. So it's important that you follow your anaesthetist's advice.

About epidural anaesthesia
How does an epidural work?
What are the alternatives?
Preparing for your procedure
About the procedure
What to expect afterwards
What are the risks?
Further information
Questions and answers
Related topics
Sources

About epidural anaesthesia

Epidural anaesthesia (also called regional anaesthesia) stops you feeling pain without putting you to sleep. Epidural anaesthesia can be given on its own, or with sedation.

Epidural anaesthesia is often used as an alternative to general anaesthesia for surgery in the pelvic area or legs. Advantages include being awake and responsive during the operation, less nausea and vomiting, and a quicker recovery afterwards. An epidural may also reduce your risk of developing a blood clot in a leg vein (deep vein thrombosis, DVT).

An epidural may be given at the end of an operation that has been done under general anaesthesia to help control any post-operative pain. This is called epidural analgesia.

How does an epidural work?

The spinal cord runs through a channel formed by the vertebrae and is surrounded by three protective membranes called the meninges.

The spinal cord carries signals, in the form of electrical impulses, between the brain and the network of nerves that branch outwards from the spine to all parts of the body.

At each level of the spine, main nerves join the spinal cord from specific parts of the body. For example the nerves from the lower part of the body join the spinal cord in the lower back.

The epidural space surrounds the outermost membrane of the spinal cord. Injecting local anaesthetic into the epidural space in the lower back blocks feeling in your pelvic area and legs. Your anaesthetist can control how much feeling is lost, depending on the amount and type of medicines used. It's possible that you may not be able to move your legs until the effects of the epidural wear off. You will also find it difficult to pass urine because you won't be able to feel when your bladder is full. You will usually have a catheter fitted until the effects of the epidural pass. This is a thin tube passed into your bladder to help urine flow.

Illustration showing the different parts of the spinal cord
The different parts of the spinal cord

Injections and infusions

A single injection into the epidural space can be used for short-term pain relief. The local anaesthetic is harmlessly broken down within a few hours and feelings in the affected area return.

Alternatively, a continuous flow of pain relief medicines can be given through a fine plastic tube (cannula) placed in the lower back and attached to a pump. This is known as an epidural infusion and is useful for longer operations or for providing pain relief over several days.

After some operations, you may be allowed to control the infusion. This is called patient-controlled analgesia or PCA. It may give better pain relief with lower doses, than when doses are set by the anaesthetist.

What are the alternatives?

Alternatives to epidural anaesthesia during surgery include spinal anaesthesia and general anaesthesia. Spinal anaesthesia involves injecting local anaesthetic into the fluid that surrounds the nerves in the lower back. The advantage of epidural over spinal anaesthesia is the ability to maintain anaesthesia for a longer period through infusion. General anaesthesia means you are asleep during the operation.

Pain medicines such as diamorphine or morphine can provide pain relief immediately after surgery. An infusion of painkilling medicine may be given into a vein through a drip. This method can also be patient controlled.

Preparing for your procedure

Your anaesthetist will explain how to prepare for your epidural. An epidural may not be suitable for you if you have a blood clotting problem or any condition affecting your nervous system or lower back. You must tell your anaesthetist if you are taking blood-thinning medicines such as aspirin, warfarin or clopidogrel.

You will stay awake during the procedure, but you may be offered a sedative to help you relax.

You may be asked to sign a consent form. This confirms that you understand the risks, benefits and possible alternatives to the procedure and have given your permission for it to go ahead.

About the procedure

You will be asked either to lie on your side, with your knees drawn up to your tummy and your chin tucked in, or to sit up on the bed and lean forward. Both positions open up the space between the vertebrae.

Your anaesthetist carefully selects a point to inject by feeling for specific bones in the spine and hips. He or she may mark this site with a pen to show where to put the injection. A small amount of local anaesthetic is injected into the skin.

When the skin is numb, a larger epidural needle is passed into the epidural space. When the needle reaches the correct spot, a cannula is inserted through the centre of the needle. The needle is removed and the cannula is left running from the epidural space to the outside.

Where the epidural is positioned

The cannula is held in place with adhesive tape. Your anaesthetist uses the cannula to inject local anaesthetic and/or other pain relief medicines directly into the epidural space. Your anaesthetist may attach a pump to the cannula to give a continuous infusion of medicines.

It's very important to stay still while your anaesthetist is preparing the site for the epidural injection and especially whilst the epidural needle is being inserted as any movement makes positioning the needle more difficult.

When the need for pain relief has passed, the cannula is carefully withdrawn and the area covered with a plaster.

What to expect afterwards

Effects of an epidural can wear off completely within two hours or with top-ups last for several hours. You will not experience the drowsiness that usually follows a general anaesthetic.

What are the risks?

An epidural is commonly performed and generally safe. However, in order to make an informed decision and give your consent, you need to be aware of the possible side-effects and the risk of complications of this procedure.

Side-effects

These are the unwanted, but mostly temporary effects of a successful procedure. Common side-effects are listed here.

Inability to pass urine - a temporary catheter is fitted until the effects of the epidural pass.
Nausea and vomiting - this is less common than with general anaesthesia.
Backache. This usually only occurs in people with a pre-existing back problem.
A drop in blood pressure - your blood pressure will be checked frequently. If it drops, you may be given medicines to correct it.
Loss of strength or control of muscles - you may not be able to move your arms or legs depending on the location of the epidural. This wears off with the anaesthetic.
Imbalance in pain relief - sometimes the medicine doesn't spread equally around the spinal cord, meaning that one half of the body is better anaesthetised that the other. A top-up dose can usually correct this.
Itchy skin - this is an allergic reaction and your anaesthetist will change the medicine to deal with this.

Complications

This is when problems occur during or after the procedure. Most people are not affected. With any procedure involving anaesthesia there is a very small risk of an unexpected reaction to the anaesthetic. Complications specific to an epidural are uncommon but can include the following.

Headache - the epidural may puncture the membrane covering the spinal cord and fluid can leak out. This puts pressure on the surrounding nerves causing headaches. These can last up to a week or maybe longer.
Bleeding - a blood vessel may be damaged and cause bleeding into the spinal cord. This may require careful observation in hospital.
Infection - this is very uncommon because the skin is cleaned before the (sterile) needle is inserted. If you develop an infection, drainage of the infected area and antibiotics may be necessary.
Long-term numbness - you may have patches of numbness lasting up to three months. Permanent damage, such as paralysis (complete loss of sensation and movement) is extremely rare.

The exact risks are specific to you and differ for every person, so we have not included statistics here. Ask your anaesthetist to explain how these risks apply to you.

Further information

World Anaesthesia Online
www.nda.ox.ac.uk/wfsa