Epidurals were developed for pregnant women to address the severe pain of labour. In Australia about one in three pregnant women in labour has an epidural for this reason.
A specialised medical doctor who has training and experience in this technique performs it in a hospital with an epidural service. This doctor is usually an anaesthetic consultant (anaesthetist) or a trainee under their supervision, or a GP anaesthetist.
An epidural is sometimes called a "major regional block" because a large region of the body has pain blocked in it, or a "neuraxial block" because it blocks the pain nerves around the middle axis of the body.
Why is it sometimes 'too late'?
A woman must request an epidural and give her consent before the procedure. The doctor then inserts an intravenous line (an "IV"). The procedure is performed between contractions, with the woman sitting up or lying on her side. It is safe to have an epidural early in labour or even before labour is induced as long as the woman has no medical reason to avoid one.
Medical reasons include conditions that increase the risk of bleeding and infection around the spinal nerves, which can lead to spinal nerve damage.
Another reason is if a woman is fully dilated or just about to give birth as there may not be time for an epidural. This is because the procedure itself takes time to perform, may be challenging to perform at this stage of labour due to pushing and the need for the woman to keep very still, and it then takes time for the medications to work.
In general, the aim is for women to have adequate pain relief 45 minutes after the epidural procedure has started. If birth is expected within this time, the risks of an epidural, outlined below, are generally thought to outweigh the benefits of possible pain relief.
How is it administered?
An epidural involves placing a very small soft plastic tube into the epidural space in the lower part of the back. The epidural space is near the spine in the central part of the back, where the pain nerves of childbirth are located.
The doctor usually delivers two different types of medications down the epidural tube into the epidural space. These are local anaesthetics (drugs like lignocaine, commonly used to numb tooth pain for dental work) and morphine-like medications (opioids).
The two different drugs work together to improve pain relief. This means less of each drug can be used so there is less likelihood of side effects. These medications then surround the nerves and block signals from the nerves to relieve pain.
The medications block mainly the small pain nerves, and not the large muscle nerves. This means a woman can still move her legs and push effectively, while getting pain relief. This is often known as a "light epidural".
One recent technique is known as patient controlled epidural analgesia. This is when a woman can press a button to control the delivery of medication into the epidural space, and so the amount of pain relief she receives.
A woman usually has to stay in bed during an epidural for labour or birth. This is because the epidural can also block some other small nerves (those that control balance), so increasing the risk of a fall.
What are the advantages?
While the major advantage of an epidural is to provide complete or near complete pain relief for labour, other advantages include reducing blood pressure spikes during the pain of contractions in women with high blood pressure (pre-eclampsia) and allowing twins to be safely delivered vaginally.
Another advantage is if the woman needs a caesarean section then the epidural can often be simply "topped up". This means the doctor delivers a different medication or an increased amount of the same medication via the epidural tube.
This leads to a much stronger epidural block causing the woman's legs to become very heavy and pain relief to extend higher up her body to her breasts. This is needed so the woman does not feel pain during surgery yet she is awake to experience the birth. In the past this type of epidural was commonly used during labour and was known as a "heavy epidural".
What are the risks?
It is important to monitor the woman and the unborn baby when a woman has an epidural because there can be changes in her blood pressure or the unborn baby's heart rate.
There is no increased risk of caesarean section with an epidural, however women who have an epidural have on average a 14 minute longer second stage of labour - when the woman is fully dilated until she gives birth. There's also an increased risk of needing instruments such as forceps during a vaginal birth (one woman in eight without an epidural compared with one in six women with an epidural).
Sometimes an epidural can fail. There may have been a failure to locate the epidural position (sometimes due to the anatomy of the woman), pain may continue 45 minutes after the initiation of the epidural, replacement of an epidural is needed if it is not working, there is patchy or one-side anaesthesia, or there is an accidental puncture in the layer of tissue around the spinal canal known as the dura.
The criteria and standards for best practice when a hospital department offers an epidural pain relief service for pregnant women include at least 88 per cent of women having adequate pain relief 45 minutes from the start of the epidural procedure, fewer than 15% of women having their epidural replaced at any point during labour, fewer than 1 per cent of women having an accidental dural puncture, at least 85 per cent of women having an excellent epidural experience overall, and at least 98 per cent of women being satisfied with their pain relief in labour.
In Australia we are fortunate to have skilled, specialised medical doctors who work as part of a team to provide pregnant women with choice, and safe and effective anaesthesia so their experience of childbirth can be pain free and enjoyable.
Alicia Dennis is a staff specialist anaesthetist and Director of Anaesthesia Research at the Royal Women's Hospital, Parkville, Australia.
This article was first published on The Conversation.