How is an epidural injection done?

Having an epidural is not really painful. Patients report that it feels “strange”, like pressure in the back.

The most sensitive part is the skin, which the anaesthetist first numbs by injecting a small amount of local anaesthetic with a tiny needle, almost as thin as a hair. Because of the small size of this needle, the patient hardly feels the injection. After a minute or so, when the skin has been numbed, the anaesthetist inserts the epidural needle, which is considerably thicker, but is not felt anymore

There are very few nerve endings or pain receptors in the tissue between the skin and the epidural space, so once the needle has passed through the skin, the procedure is hardly painful at all. The epidural needle is inserted to a depth of 2-4 cm, where the epidural space will be encountered.

The anaesthetist employs a “loss of resistance” technique to know when the needle tip has reached the epidural space: a syringe is attached to the epidural needle, which is gradually pushed further below the skin in the direction of the epidural space. With his/her thumb, the anaesthetist keeps continuous pressure on the plunger of the syringe. When the tip of the needle reaches the epidural space, which has a lower resistance than the surrounding tissues, the plunger will suddenly drop into the syringe (“loss of resistance”).

The syringe is then disconnected and through the needle a very thin plastic catheter of about 0.5 mm is threaded into the epidural space. The needle is removed and the catheter stays behind for as long as pain relief is needed. It is so thin and soft that the patient is never aware of its presence (there is no needle left behind in the back once the catheter is in place). The catheter allows the anaesthetist to prolong pain relief by administering a continuous infusion of local anaesthetic for a few days.

A single shot of local anaesthetic would wear off after a few hours, but after most, if not all, operations, longer pain relief is required, which is made possible by continuous infusion.

Reviewed by Prof CL Odendal, senior specialist at the department of anaesthesiology at the University of the Free State, April 2010.

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