An epidural (meaning ‘above the dura’) is a form of local anaesthetic used to completely block pain while a patient remains conscious. It involves the careful insertion of a fine, long needle deep into an area of the spine between two vertebrae of the lower back.
This cavity is called the epidural space. Anaesthetic medication is injected into this cavity to relieve pain or numb an area of the body by reducing sensation and blocking the nerve roots that transmit signals to the brain.
The resulting anaesthetic medication causes a warm feeling and numbness leading to the area being fully anaesthetised after about 20 minutes. Depending on the length of the procedure, a top-up may be required.
This form of pain relief has been used widely for many years, particularly postsurgery and during childbirth.
1. Epidural space – The outer part of the spinal canal, this cavity is typically about 7mm (0.8in) wide adults.
2. Epidural need – After sterilising the area, a needle is inserted into the interspinous ligament until there is no more resistance to the injection of air or saline solution.
4. Absorption – Over-about 20 minutes the anaesthetic medication is broken down and absorbed into the local fatty tissues.
5. Radicular arteries – The anterior and posterior radicular arteries run with the ventral and dorsal nerve roots, respectively, which are blocked by the drug.
6. Processing – Anaesthetic in the blood is filtered out by the liver and kidneys, then leaves the body in urine. The effects usually wear off a couple of hours after the initial injection.