An epidural is usually done with the patient awake or slightly sedated so that they can cooperate and provide verbal feedback. The patient will either sit up or lie on their side. The skin on the back is cleaned with an antiseptic. The anesthesiologist will feel the spine to identify landmarks, and then anesthetic “freezing” is injected into the skin, which stings for a short while. Anesthetic is then injected deeper down into the ligaments and, at the same time, branches of the nerves supplying the thick back muscles and the lining of the bony vertebrae are frozen.

The epidural needle is then directed towards the ligament overlying the epidural space. The needle is relatively blunt and is slowly pushed forward through the tissues.

It should not be uncomfortable, but you may feel firm pressure and pushing as the anesthesiologist advances the needle. The epidural space is reached when the tip of the needle passes through the ligament. The anesthesiologist knows this space has been reached by feeling a decrease in resistance to the needle.

At this stage the catheter is passed through the needle into the epidural space. As the catheter enters the space, it may come into contact with a nerve root – this would cause a local, sharp sensation that should disappear rapidly. The needle is removed over the catheter.

A test dose of local anesthetic is sent through the catheter to confirm that the catheter tip is in the right place, and a dressing is placed over the catheter insertion site to hold the catheter in place.
Epidural catheters make possible excellent pain control from small amounts of pain drugs

Local anesthetics injected through the catheter will block all types of nerve messages. By changing the type, concentration and amount of drug injected, the anesthesiologist can “freeze ” a large area of the body, or can freeze only the nerves that would conduct pain sensations from the surgical site. This allows the surgical site itself to be numb, while giving the patient the ability to move their muscles spontaneously, so they can move around after surgery.

Opioids are often injected into the epidural space, either alone or combined with the local anesthetic agents. The spinal cord has natural opioid receptors. By delivering an opioid so close to these receptors, only very small amounts of the drug are needed to achieve excellent pain control. Using such small quantities may reduce some of the side effects of opioids that can happen at higher doses.

Also, using a combination of different drugs in the epidural space allows the dose of any single drug to be reduced, which cuts down on the side effects of each drug while maintaining good pain control.