What is epidural anesthesia?

The brain and spinal cord are bathed in a fluid, called cerebrospinal fluid, which is held within a multilayered membrane whose main component is called the "dura."

Epidural anesthesia is accomplished by using a needle to inject small amounts of medication (mainly "local anesthetics" similar to those used for dental procedures) into the patient's back in a space that is located just outside of the "dural membrane" where it contacts nerves going to and from the spinal cord.  This cases the pain impulses to be anesthetized (or blocked) so that they do not reach the brain.  

In obstetrics, a thin plastic tube is passed through the needle to allow continuous infusion of the anesthetic so that its effects will not wear off until after the labor and delivery are completed.