"Epidural" is a commonly used word amongst women. They are aware that an "epidural" can be used to numb the body from the waist downwards during childbirth. Many also know this is performed by a "needle in the back".

However, the medical term epidural actually means "around the membranes that surround the central nervous system". The brain and spinal-cord is surrounded by a series of membranes called the dura. The outer most layer is called the dura mater. In the spinal column, there is a space outside of the dura matter but inside of the bone - is called the epidural space (or extradural space).

Therefore the term epidural, really just means this space.

The use of epidural anaesthesia, particularly in labour, but also in people requiring surgery of their abdomen, pelvis or the legs in whom the general anaesthesia is not required or could be dangerous, has stemmed from the particular anatomy of this space. As all of the nerves leave the spinal cord and pass out through holes between the bones (the foramens between the vertebrae), if local anaesthetic is used to fill this epidural space, all of the nerves will be affected.

Therefore, if a skilled anaesthetist can pass a hollow needle through the skin, ligaments and between the bones of the spine (vertebrae) and gets the tip within the epidural space, a very fine tube called an epidural catheter can be passed into this space for the administration of local anaesthetic. Depending on the strength of the local anaesthetic and volume used, the legs pelvis and lower abdomen (occasionally upper abdomen) can be completely numbed.

Although epidurals have made a massive difference to many women in labour, as well as many other patients requiring surgery to the lower parts of their body, it isn't without risk.

Most of these risks are related to the passage of the needle passing between the vertebrae, and entering the epidural space. If the needle goes a little too far forwards, the dura mater can be pierced resulting in a leak of the cerebrospinal fluid (CSF) - which is the fluid that bathes the brain and the spinal-cord. In addition, a blood vessel can be accidentally hit, resulting in a bruise within the epidural space. As this is surrounded by rigid bone, if this bruise expands, it will press against the spinal-cord and can have severe effects if it crushes the sensitive nerves.

As with all areas of medicine, the tremendous benefits if everything goes well but, there can be risks if things go wrong, and even if no one is at fault.

Therefore, if appropriate, all patients should know exactly the pros and cons of having any intervention such as an epidural, before consenting to have it. Unfortunately, because Labour is often of sudden onset, and can be excruciatingly painful, women are being offered an epidural can be unable to consider the options and give informed consent. Similarly, patients with emergency procedures requiring an epidural for anaesthetic, can be in the same situation of not being able to provide adequate consent.

Although epidural is an excellent procedure when used in the correct patient and when it goes well, because of its anatomy and the place it is often most useful, it is often the subject of complaints, complications and unfortunately litigation.