An epidural is a procedure to provide anaesthesia for surgery, and/or to control pain afterwards. It is carried out by an anaesthetist and involves injecting local anaesthetic or painkilling drugs into the epidural space that surrounds the spinal cord. Epidurals are also used for pain relief during childbirth
Epidural anaesthesia is an alternative to having a general anaesthetic. The possible advantages include being awake and responsive during the operation, less nausea and vomiting and a quicker recovery afterwards.
How does an epidural work?
The spinal cord runs through a channel formed by the vertebrae and is surrounded by a series of three protective membranes called the meninges (pronounced men-in-jees).
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. 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. An injection of local anaesthetic into the epidural space in the lower back results in a loss of sensation in the pelvic region and legs.
The anaesthetist can control how much sensation is lost, depending on the amount and type of drugs used. Even major surgery can be done without any sensation of pain, but no loss of consciousness.
Injections and infusions
A single injection into the epidural space can be used for a short operation, or for short-term pain relief. The local anaesthetic is harmlessly broken down within a few hours. As the epidural wears off, feeling in the legs gradually returns.
Alternatively, a continuous flow of drugs can be given through a fine tube placed in the lower back and attached to a pump. This is is known as an epidural infusion and is useful for longer operations or for providing pain relief over several days.
After some operations, the patient has control of the infusion. This method is a type of patient-controlled analgesia. It may give better pain relief, with lower doses of drugs, than when drug doses are set by the anaesthetist.
What does it feel like?
Sometimes people still feel the sensation of movement, warmth or cold in their legs. But there will be no pain and the legs usually feel numb.
As well as blocking pain signals towards the brain, an epidural may block the signals from the brain. This affects the ability to control the leg muscles. As a result, walking may be difficult or impossible. Low-dose epidurals, which make walking possible tend to be offered to women during labour.
Before the epidural
We will discuss your health with you beforehand. Epidurals may not be suitable for people who have any neurological problems (problems affecting the nervous system), blood clotting problems, or those who have had back problems.
What to expect
The patient is asked either to lie on their left side, with the knees drawn up and chin tucked in, or to sit on the bed or a chair and lean forward. Both positions tend to open up the space between the vertebrae.
The anaesthetist carefully selects a point to inject by feeling for specific bones in the spine and hips. He 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.
After a minute or so, when the skin is numb, the anaesthetist will insert the larger epidural needle through the skin and towards the epidural space. When the needle reaches the correct spot, a fine plastic tube (cannula) is inserted through the centre of the needle. The needle is then removed, leaving the cannula running from the epidural space through the skin to the outside.
The cannula is held in place with adhesive tape. The anaesthetist can then use the cannula to inject anaesthetic or painkilling drugs directly into the epidural space. The injection can be repeated to top up the effect of the first. Or a pump can be attached to the cannula to give a continuous infusion of drugs.
While the anaesthetist is preparing the site for the epidural injection and especially whilst the epidural needle is being inserted, it is very important to stay still, as any movement makes positioning the needle more difficult.
Once the need for pain relief has passed, the cannula is carefully withdrawn and the area covered with a plaster.
Deciding to have an epidural
An epidural is a commonly-performed and generally safe procedure. However, in order to give informed consent, anyone planning to have an epidural should be aware of the risk of side–effects and complications.
Side-effects are the unwanted but usually mild and temporary effects of a successful procedure. These can include the following.
- Inability to pass urine. If this occurs, a urinary catheter can be inserted into the bladder temporarily.
- Nausea and vomiting. Although this can occur, it is much less common than with general anaesthesia.
- Backache. This is thought to result from the relaxation of the back muscles after the epidural anaesthetic has been inserted.
- A drop in blood pressure. After the epidural drug is given, the anaesthetist will check your blood pressure frequently. If your blood pressure falls, then it may be necessary to give drugs and more fluids through a drip.
- Loss of leg strength or control of the leg muscles. This wears off with the anaesthetic.
- Imbalance in pain relief. Sometimes after the epidural anaesthetic is given, the drug does not 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. Some of the drugs used for epidurals can causes itchiness. The anaesthetist can change the drug to deal with this.
Complications are unexpected problems during or after the procedure. Most people are not affected. They can include:
- Headache. If the epidural needle nicks the covering of the spinal cord, there may be a small leak of fluid from around the cord, which can cause a headache when you sit or stand up. This can last for up to a week.
- Bleeding. There are many blood vessels around the spinal cord and occasionally one will be pricked as the epidural needle goes in. This requires careful observation in hospital.
- Infection. This is uncommon because the skin is cleaned before the (sterile) needle is inserted. However, if there is an infection, drainage of the infected area and antibiotics may be necessary.
- Longer-term numbness. Some people have patches of numbness lasting up to three months. Permanent damage, such as paralysis (complete loss of sensation and movement) is very rare.