What is an epidural?

An epidural is a local anaesthetic introduced into the epidural space; this is the space surrounding the spinal column. It can be given as a single shot or as an infusion.

Epidurals are used in many different areas of anaesthesia. The most common use is for women in labour. However, epidurals are also used in many cases when patients are undergoing an operation as well as for pain management; for example, chronic pain and patients with back pain.

An epidural is performed using a small plastic catheter that remains in the back and is attached to a local anaesthetic infusion.

How is an epidural administered?

An epidural injection is conducted under sterile conditions. Before the anaesthetist starts, the back will be cleaned and sterile drapes will be applied to the body.

Following this, the anaesthetist will freeze the skin where he or she is going to insert the epidural by using a small needle to inject some local anaesthetic. This means that the patient will not feel the epidural needle when it is injected.

It is a safe technique because as the epidural needle is inserted, a syringe is inserted onto the end. The needle is used to find the epidural space surrounding the spinal column. It is inserted between the bones and the lower part of the back.

The needle is advanced very slowly and at the same time pressure is applied gently to the syringe. This is so that the anaesthetist can feel all the layers as he or she passes the needle through them and make sure the needle is advancing safely and in the correct direction towards the epidural space.

Just before the needle reaches the epidural space it will pass through a ligament called the ligamentum flavum. This is quite gritty and the anaesthetist will feel an increased amount of resistance from the needle.

At this point, the epidural space is very close, so the needle is just advanced a very small amount further until there is a very sudden and convincing loss of resistance which means the epidural space has been reached.

The syringe is then removed and the epidural catheter is inserted. This is just a very fine plastic tube which is threaded through the needle and remains in the body when the needle is removed.

Many patients are concerned that an epidural injection means that a needle will remain in their back but the needle is removed and all that remains in the body is a very fine plastic tube to administer the local anaesthetic through.

Once the epidural injection has been performed the patient is able to lie back and function normally. There is no concern about damage from the way the patient lies.

The catheter is attached to a filter, which is also sterile to reduce any risk of an infection being introduced to the body. Local anaesthetic is attached to the filter and a gradual amount of local anaesthetic is infused into the body through the catheter and the body that is distal to this part of the catheter then gradually gets numbed.

Dr Daman Mulhi, Anaesthetic Consultant, NHS
Specialist in anaesthesia, diabetes, obesity, metabolic syndrome, and public health awareness