Layers through which epidural needle goes

For epidural anesthesia, the styletted epidural needle is inserted through the skin and subcutaneous tissue, the supraspinous and interspinous ligaments, and into the ligamentum flavum. The stylet is removed from the needle, and a loss of resistance syringe containing saline, air, or a combination of the two is firmly attached to the needle hub. As the needle is advanced, the epidural space is identified by loss of resistance to injection of air or saline. The syringe is then removed, and an epidural catheter is advanced through the needle and into the epidural space. The needle is removed over the catheter, leaving 4 to 6 cm of the catheter in the space. For further details refer to UpToDate content on epidural technique.