 The anxiolytic clonidine, or the nonopioid analgesic ziconotide, and local anesthetics such as bupivacaine, ropivacaine or tetracaine may also be infused along with the opioid.The outermost, protective sheath surrounding the spinal cord is called the dura mater.Between this and the surrounding vertebrae is the epidural space, filled with connective tissue, fat and blood vessels, and crossed by the spinal nerve roots.