Ketamine is approved by the U.S. Food and Drug Administration (FDA) to be used: as an anesthetic and analgesic (painkiller). Ketamine is an "adjuvant," which is a drug that may increase the effectiveness or strength of other drugs when given at the same time. Ketamine is administered as an adjuvant during anesthesia to produce anesthetic and analgesic-sparing effects (reduce the amount of anesthetics and narcotics-painkiller drugs), hemodynamic stability (to maintain the blood pressure and heart rate within normal rank) and side effect reduction (e.g., constipation, nausea and vomiting, itching, and urinary retention). Ketamine will be used as approved in this study. Ketamine is frequently used intraoperatively for pain control in patients undergoing spine surgery at our institution and is within the standard of care. The standard of care indicates that this is one possible method which has been demonstrated to be safe and effective for patient care. This may vary at different institutions.