Contrast and Anesthetic Level With Lumbar Erector Spinae Plan (ESP) Block

As per usual care for spine surgery, participants will have their back cleaned with alcohol and a needle will be placed using ultrasound for the ESP block. Through the needle, a small catheter will be placed in the participants back and the needle removed. Approximately one hour prior to the start of surgery, a numbing medication (ropivacaine, similar to Novocaine) in combination with dexmedetomidine (a pain medicine that is used in nerve block and that is not a narcotic) and contrast dye (iohexol) will be injected through the catheter. Participants will then go through the QST procedure (test of buzzing sensation and temperature sensation through pads applied to their skin) to assess the numb areas and then head to the operating room. In the operating room, the catheter will be removed after the surgeon obtains baseline CT scan images of the spine. Once surgery is completed, investigators will record pain scores over the next four days in the hospital and the amount of pain medication needed for controlling pain related to the surgery.