Epidural injection
The epidural route is very common and very practical in anesthesia because it allows several nerve roots to be anesthetized with a single injection site (direct injection or by a catheter). The epidural space (also called the epidural) is the space between the meninges (the dura mater representing the outermost layer) and the bone in the spinal canal. It is the same route that is used in the treatment of chronic pain, but with other drugs because a more lasting effect is sought.
Indications:
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Epidural lipomatosis: Epidural lipomatosis is an excess of fat located in the spinal canal. This epidural fat causes compression of the dural sac and an effect similar to a narrow lumbar canal due to osteoarthritis (the two can also be combined). An epidural injection can in these patients not only lead to a regression of pain, but sometimes a redistribution of local fat, which decreases the compressive effect on the dural sac.
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Multiradicular involvement: When several nerve roots are affected, a very targeted treatment, such as a facet block, does not allow to act on all the nerves involved and epidural injection may therefore be a good option for these patients .
Risks and disadvantages of epidural injections:
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If the needle is advanced too deeply, it can pierce the meninges (the dura, then the arachnoid). Two unfortunate consequences can result:
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This can cause cerebrospinal fluid (CSF) to leak with potentially symptoms like headaches. If this fluid leak is symptomatic, it can be blocked by injecting the patient's blood into the epidural space (blood patch).
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The needle may also hit a nerve root, which the patient will experience as an electric shock if the injection is not given while sedated. If no injection of steroids is made into the nerve root or the CSF, there is practically no clinical consequence. It is therefore imperative to make the wrong placement of the needle, which is why epidural injections for the treatment of pain are always done under fluoroscopic control and with injection of contrast product before injection of the drug.
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A hematoma in the epidural space can cause compression of the dural sac with potentially cauda equina syndrome (involvement of multiple lumbar and sacral roots) or even spinal cord compression if the hematoma bursts in the cranial direction. It is therefore imperative to be very careful in patients with coagulation disorders or anticoagulation (Sintrom, Heparin, Xarelto, ...) or anti-aggregation drugs (Aspirin, Plavix, ...).
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The epidural space is filled with fat, but also very well vascularized. The drugs injected into this space therefore have the disadvantage of being eliminated very (too) quickly. As the volume of distribution is relatively large, this decreases the local effect of the drugs injected.
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If a lesion is already present in the spinal canal (hernia, tumor, ...) or if the spinal canal is narrow, then the epidural injection can temporarily increase the compression on the nerve roots by volume effect.
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The use of drug in depot form is also debated in epidural. From our point of view, there are no risks when the gesture is performed correctly. It is likely that the complications for this type of product result from two errors: either an intrathecal injection or an intra-vascular injection. This reinforces the need for an epidurography before injection of drugs to ensure that the needle is neither intrathecal nor intravascular.
Volume effect:
This diagram illustrates the problem of the volume effect. The intracanal space is already reduced due to the presence of the herniated disc. The epidural injection transiently increases the compression on the root and the dural sac.
