![]() Local anesthetic must be administered as described for the medial approach. In the paramedian approach, the insertion site of the needle is 1 cm lateral to the vertebral interspace. Once the ligamentum flavum is pierced, a loss in resistance will be noted this is the epidural space, and 5 to 10 cc of saline may be injected to expand the epidural space this may decrease the risk of vascular injury. The needle must be advanced while applying pressure to the plunger. Once there, the stylet must be removed, and the Loss of Resistance syringe (filled up with saline, air, or both) must be attached to the needle. The epidural needle must be advanced through the skin, subcutaneous tissue, supraspinous, and interspinous ligaments. Once achieving local anesthesia, the epidural needle must be advanced with its stylet in place and with its bevel point cephalad this will ultimately contribute to the proper location of the epidural catheter. Upon locating the desired spot, lidocaine 1% must be injected into the skin and underlying tissues to decrease the discomfort with the advancement of the epidural needle. In the medial approach, the site of the insertion of the needle is between the spaces created by the vertebral spinous processes. Medial (midline) and Paramedian Approaches More superficially, the remaining layers are the ligamentum interspinale (located between the spinous processes), ligamentum supraspinale (located on the surface of the spinous processes), subcutaneous tissue, and skin. The epidural space has a dorsal limitation by the ligamentum flavum. It may be 4 cm in normal-weight adults to 8 cm or more in obese patients. The distance between the skin and the epidural space is variable depending on factors like age or weight. These vessels may dilate with gravidity or ascites, which increase the likelihood of bloody puncture. ![]() The spinal epidural space contains fatty and connective tissues as well as vessels and lymph channels. It envelopes the brain intracranially, the spine, and it also extends out through the foramina intervertebralia to the epineural connective tissues of the spinal nerves. The dura is attached to the spine by its outer endosteal portion. The arachnoid is close to the dura mater. The arachnoid (and subarachnoid space) extends caudally in the adult to S2, to S3 in children, and S4 in the newborn. The spinal cord is suspended in Cerebrospinal Fluid and surrounded by the arachnoid membrane. Below this level, the lumbar and sacral nerves converge to form the cauda equine. It ends at L1 in 50% of the adults and L2 in about 40%. The spinal cord is about 45 cm shorter than the spinal canal in the adult.
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