An epidural is a procedure in which a needle is inserted into the epidural space outside the spine and local anesthetic or analgesics (painkillers) are injected. An epidural is often used to to control labour pain or to provide analgesics before, during, or after surgery. Depending on the site of the operation and your health, an epidural may be used by itself, with sedation, or a general anesthetic.

The spine contains the spinal cord and nerves as well as spinal fluid. It is contained within a sac called the dura. The epidural space is the layer outside the dura, which is surrounded by dense ligaments and other tissue. The epidural procedure gives the anesthesiologist the ability to precisely target and customize the delivery of local anesthetic medications and analgesics such as fentanyl.

When is epidural anesthesia or analgesia used?

Epidurals are frequently used to control labour pain, and they can also be used to administer the primary anesthetic for a caesarean section. They may also be used to treat certain types of chronic pain and for people receiving palliative (end-of-life) care.

In addition, they are now frequently recommended for major surgical procedures, often combined with a general anesthetic. The epidural is then continued well into the postoperative period to improve pain management.

Epidural Placement

Epidural placement

Epidurals are most beneficial for major surgery on the lungs, upper abdomen, pelvis, or legs. The use of an epidural is even more important if you have a condition that could complicate your recovery from surgery, such as obesity, angina, peripheral vascular disease, or lung disease such as emphysema. Good pain management in these cases allows you to breathe deeply and move around much earlier, decreasing the chances of developing pneumonia or blood clots.

How an epidural is done

A specially designed needle is used to reach the epidural space (see Figure 1). The medications can be injected directly through the needle or, more frequently, a tiny catheter (tube) is inserted through the needle. The needle is then removed, leaving the catheter in place. A catheter allows for the continuous delivery of medications, usually using a special pump. This pump gives precise control of the medications, and can allow you the ability to partially adjust the medication delivery until the desired pain relief is obtained (called patient-controlled epidural analgesia).

Epidural: What to expect

An epidural is usually done while you are awake or slightly sedated so that you can follow instructions and provide verbal feedback. You will either sit up or lie on your 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 time.

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 covering 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: Controlling pain using small amounts of pain medications

Local anesthetics injected through the catheter will block all types of nerve messages. By changing the type, concentration, and amount of medication 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 you the ability to move your muscles spontaneously, so you can move around after surgery.

Opioids are often injected into the epidural space, either alone or combined with the local anesthetics. The spinal cord has natural opioid receptors. By delivering an opioid close to these receptors, only very small amounts of the medication 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 medications in the epidural space allows the dose of any single medication to be reduced, which cuts down on the side effects of each medication while maintaining good pain control.

Epidural: Side effects and complications

The potential for side effects and complications exists with any form of anesthesia. However, studies have shown that epidural anesthesia is very safe.

Local anesthetic medications administered into the epidural space spread to anesthetize nerves in the area. Depending on the medication concentration and amount, weakness of the limbs and abdominal or chest wall muscles may occur. Sometimes, a reduction in blood pressure and a decrease in heart rate may occur. Opioids in the epidural space may also cause slower breathing, drowsiness, itching, urinary retention, and nausea. Side effects are common, but with constant care from the medical team, their effects can be minimized or even prevented.

These complications are unlikely, but may occur:

  • During needle insertion, you may experience pain from the places that are pierced by the needle. This pain may persist for a short time.
  • The needle may puncture the dura and enter the spinal space. This could result in a headache and if severe may require a blood patch. This involves injecting your blood into the epidural space to patch the hole made in the dura by the spinal needle. 

These complications may also occur, but are very rare:

  • The needle or catheter may touch a spinal nerve or even the spinal cord. Although this usually has temporary effects (mainly pain), some very rare instances of permanent nerve damage have been reported. 
  • Bleeding within the epidural space causing an epidural hematoma, which may compress the neural structures. If unrecognized, this could lead to paraplegia; although this is a very rare occurrence.
  • Interruption of the arterial blood supply to the spinal cord causing variable spinal cord damage. 
  • Bacteria could be introduced into the epidural space causing an infection or even an abscess. 
  • Local anesthetics could enter the spinal space and mix with the spinal fluid causing a high spinal block affecting the ability to breathe. 
  • A large amount of concentrated local anesthetic may enter the blood vessels through a catheter tip that has entered a vein. This may result in seizure, heart rhythm disturbances, or both.
  • The injected local anesthetic, opioid, or any preservative may cause a chemical toxicity to the nerve tissue. 

Issues surrounding epidural use

It was originally thought that placing an epidural catheter into the thoracic (upper spinal) epidural space was more risky than a lumbar (lower spinal) epidural. However, studies have failed to show any difference in risk. Epidural catheters for controlling postoperative pain are now routinely placed in the thoracic region.

There is also a concern for people using low-molecular-weight heparin medications (e.g., enoxaparin, dalteparin) that are now commonly used to prevent deep vein clots. People taking these medications seem to have an increased risk of epidural hematomas (build-up of blood in the epidural space). Current recommendations vary, but you should wait after your last dose of low-molecular-weight heparin before receiving an epidural catheter and following its removal.