Like methadone, ketamine is used most frequently in patients undergoing spinal fusion surgery due to the high incidence of pre-existing opioid tolerance and hyperalgesia (personal communication). Ketamine infusions have been investigated in 6 randomized studies in this patient population. In 5 of the trials, reduced postoperative opioid requirements, decreased pain scores, or both, were observed in patients randomized to receive ketamine. Shorter-acting opioids were used with ketamine in 5 of the investigations. Despite data suggesting a beneficial effect of ketamine in patients undergoing major spine surgery, a recent "best evidence" review stated that "there is insufficient and /or conflicting evidence that ketamine provides a significant reduction in postoperative pain or narcotic usage"