Some anaesthetists use a morphine-like "opioid" painkiller mixed with the local anaesthetic to enhance its effectiveness.
Once the catheter is in place on the anaesthetic solution is injected, pain relief takes about 10 minutes. The catheter remains in place throughout labour.
Pain relief during labour is maintained by: 
Other Benefits of Epidural Anaesthesia for You:  An epidural usually does not cause sedation, which is important for women who want to be alert during their birth experience.  For medical reasons, an epidural may be necessary in some cases of premature labour, delivery of twins, breech delivery, or mothers with high BP.
The epidural can reduce the stress caused by pain. As the woman relaxes, breathing and BP return to normal, the workload on the heart is less and the blood flow to the uterus improves. In most cases this improves the well-being of the baby.
As the catheter stays in place, more epidural anaesthetic can be administered easily if another procedure becomes necessary, such as forceps-assisted delivery, caesarean section, or removal of a retained placenta.
After delivery, it may be possible to continue to use the epidural for further pain relief, especially after caesarean section.

The decision to have an epidural.
Decisions about an epidural anaesthetic are made after discussion with your Anaesthetist and Obstetrician. Although the choice is normally up to the mother, the Obstetrician may recommend an epidural for medical reasons. Any decision should not be made in a rush, but rather when you're satisfied with, and understand, the information you have received.
Your Anaesthetist cannot guarantee that an epidural will always be completely successful, that there is no risk, or that you will be satisfied with degree of pain relief. Although many mothers have made up their minds in advance, others prefer to wait until labour is underway and then decide whether they want an epidural. If you decide to have an epidural, your Anaesthetist may ask you to sign a consent form. Read carefully. If you have any questions about the consent form, ask your Anaesthetist.

Before The Epidural: 
Your Anaesthetist needs to know your complete medical history, as well as details of allergies and medications which you may be taking, including insulin, blood thinners such as Warfarin and medications such as Aspirin. Your Obstetrician and Anaesthetist will advise you about any medications which you may need to continue or stop taking.

Tell your Anaesthetist if you have had:
  1. an allergy or bad reaction to local or general anaesthetic
  2. any other medicines or drugs which you take. This includes herbal or naturopathic medicines as these can have interactions and side effects
  3. a bleeding disorder or easy bruising
  4. long-term or recent illnesses
  5. a heart disorder
  6. surgery to the lower back.
Possible Side-effects And Complications of Epidural Anaesthesia:  Epidural anaesthesia is safe and effective, but does have the risks. Serious problems during or following epidural anaesthesia are uncommon. Despite the highest standards of training and practice, side-effects and complications are possible, not only with epidural anaesthesia but also with all types of procedures and treatment in modern medicine. While your Anaesthetist is highly trained and makes every attempt to minimise risks, complications may rarely occur which could have permanent effects.
When informing a patient about any type of anaesthesia or treatment, it is not usual for a doctor to discuss in great detail all the possible side-effects or rare, serious complications. The following possible risks are listed to inform you, not to alarm you. It is important to remember that even the most natural childbirth with no medical assistance can still carry risks for both the mother and baby.

Common side-effects for the mother:

In some patients, precise placement of the epidural catheter by the Anaesthetist can be difficult, especially if the patient is short or obese.
In about 1 in every 100 women who opt for the procedure, the dura may be punctured by the needle, and cerebrospinal fluid may leak into the epidural space. This leak may cause a moderate to severe headache which usually responds to simple treatment. If untreated, this headache may last for 4 or 5 days. Although temporary, it can be severe enough to interfere with breastfeeding and routine care of the baby. In the unlikely event of this complication, your Anaesthetist will advise appropriate treatment.
Some earlier studies suggested that epidural anaesthesia may prolong labour and may increase the likelihood of forceps delivery, episiotomy or a caesarean delivery. However, more recent studies have disputed this. Even if an epidural does affect a particular labour, there is no evidence that this will harm the baby or mother in a properly managed labour. In most situations, the epidural offers real benefits to both mother and baby.

Allergic reactions to the local anaesthetic. This is extremely rare.

Serious complications: 
Serious complications are very rare. Anaesthetists are specially trained to recognise and promptly treat situations which may be life-threatening or permanently debilitating.
The site of puncture and the region surrounding the spinal cord can become infected. This is a serious condition requiring treatment with antibiotics or, rarely, surgery.
The local anaesthetic solution may be injected inadvertently into a blood vessel, causing dizziness, a metallic taste in the mouth, and in extreme cases, convulsions and heart problems.
Reports in the world's medical journals have linked permanent paralysis and death to epidural but the cases are so rare in modern practice that the precise risks are not known.
Temporary damage to nerves outside the spinal cord may occur about 1 in 3000 women. Virtually all of these cases heal within 12 weeks. The temporary nerve damage may be caused by the labour rather than by the epidural procedure.

Possible complications for the baby. Local anaesthetic and opioid medications appear to have little or no effect on the baby. Reports of toxic effects of local anaesthetic and opioid drugs have been largely discounted.
If a labour becomes prolonged or blood pressure falls, the baby may become distressed, possibly leading to medical intervention such as forceps-assisted or caesarean delivery.