 Anesthetic management for this study will be exactly the same management that we are currently providing for patients undergoing multilevel spinal fusions. The only difference in care between the placebo group and the treatment group will be the addition of a low dose ketamine infusion in the treatment group. The placebo group will receive a fentanyl infusion at 1 mcgkghr during the surgery and a morphine PCA for postoperative pain control. The placebo group will receive additional fentanyl as needed on the operating room and additional morphine as needed in the recovery room. 