Anatomy Sagittal section of the spinal column (not drawn to scale). Yellow: spinal cord; blue: pia mater; red: arachnoid; light blue: subarachnoid space; pink: dura mater; pale green: epidural space; taupe: vertebral bones; teal: interspinous ligaments An epidural is injected into the epidural space, inside the bony spinal canal but just outside the dura. In contact with the inner surface of the dura is another membrane called the arachnoid mater, which contains the cerebrospinal fluid. In adults, the spinal cord terminates around the level of the disc between L1 and L2, while in neonates it extends to L3 but can reach as low as L4. Below the spinal cord there is a bundle of nerves known as the cauda equina or "horse's tail". Hence, lumbar epidural injections carry a low risk of injuring the spinal cord. Insertion of an epidural needle involves threading a needle between the bones, through the ligaments and into the epidural space without puncturing the layer immediately below containing CSF under pressure. Insertion Simulation of the insertion of an epidural needle between the spinous processes of the lumbar vertebrae. A syringe is connected to the epidural needle and the epidural space is identified by a technique to assess loss of resistance<unk>  is a procedure which requires the person performing the insertion to be technically proficient in order to avoid complications. Proficiency may be trained using bananas or other fruits as a model. The person receiving the epidural may be seated, or lying on their side or stomach. The level of the spine at which the catheter is placed depends mainly on the site of intended operation – based on the location of the pain. The iliac crest is a commonly used anatomical landmark for lumbar epidural injections, as this level roughly corresponds with the fourth lumbar vertebra, which is usually well below the termination of the spinal cord. The Tuohy needle, designed with a 90-degree curved tip and side hole to redirect the inserted catheter vertically along the axis of the spine, may be inserted in the midline, between the spinous processes. When using a paramedian approach, the tip of the needle passes along a shelf of vertebral bone called the lamina until just before reaching the ligamentum flavum and the epidural space. Along with a sudden loss of resistance to pressure on the plunger of the syringe, a slight clicking sensation may be felt by the operator as the tip of the needle breaches the ligamentum flavum and enters the epidural space. Saline or air may be used to identify placement in the epidural space. A systematic review from 2014 showed no difference in terms of safety or efficacy between the use of saline and air for this purpose. In addition to the loss of resistance technique, direct imaging of the placement may be used. This may be conducted with a portable ultrasound scanner or fluoroscopy (moving X-ray pictures). After placement of the tip of the needle, a catheter or small tube is threaded through the needle into the epidural space. The needle is then withdrawn over the catheter. The catheter is generally inserted 4–6 cm into the epidural space, and is typically secured to the skin with adhesive tape, similar to an intravenous line. Use and removal If a short duration of action is desired, a single dose of medication called a bolus may be administered. Thereafter, this bolus may be repeated if necessary provided the catheter remains undisturbed. For a prolonged effect, a continuous infusion of medication may be used. There is some evidence that an automated intermittent bolus technique may provide better pain control than a continuous infusion technique even when the total doses administered are identical. Typically, the effects of the epidural block are noted below a specific level or portion of the body, determined by the site of injection. A higher injection may result in sparing of nerve function in the lower spinal nerves. For example, a thoracic epidural performed for upper abdominal surgery may not have any effect on the area surrounding the genitals or pelvic organs. Combined spinal-epidural techniques For some procedures where both the rapid onset of a spinal anesthetic and the post-operative analgesic effects of an epidural are desired, both techniques may be used in combination. This is called combined spinal and epidural anesthesia (CSE). The spinal anesthetic may be administered in one location, and the epidural at an adjacent location. Alternatively, after locating the epidural space with the Tuohy needle, a spinal needle may be inserted through the Tuohy needle into the subarachnoid space. The spinal dose is then given, the spinal needle withdrawn, and the epidural catheter inserted as normal. This method, known as the "needle-through-needle" technique, may be associated with a slightly higher risk of placing the catheter into the subarachnoid space.
Epidural administration
Epidural blood patch
Nerve induction
Neurosurgical anesthesia
Intrathecal pump
Epidural steroid injection
Spinal manipulation
Neurostimulation