Ketamine in Patients Undergoing Anterior Cervical Discectomy and Fusion

Ketamine is an IV anesthetic with non-opioid analgesic properties that has been shown to reduce pain while also decreasing intraoperative and postoperative opioid requirements when used in subanesthetic doses after a variety of surgical procedures.1 It is a non-competitive antagonist of N-methyl-D-aspartate (NMDA) receptors, and by this mechanism ketamine is believed to block the development of central sensitization and wind-up phenomenon,2,3 which may be helpful in preventing acute and chronic pain after repetitive insults. In a systematic review of ketamine as an adjuvant to opioid analgesia, low-dose ketamine was found to be a useful addition to standard postoperative pain management practice with opioids in 54% of studies.1 The studies that did not show a significant effect were in patient populations with low opioid requirements. Therefore, it has been suggested that future clinical trials be focused on patient populations with significant post-operative pain, such as spine surgery and major orthopedic surgery not amenable to regional analgesia, and postoperative pain in patients on chronic preoperative opioid therapy.1 There are few studies examining outcomes after ketamine in the perioperative period after spine surgery. Loftus et al randomized patients with a history of chronic preoperative opioid use (i.e., daily opiate use for at least 6 weeks) to intraoperative ketamine versus placebo and found a 30% reduction in morphine consumption at 48 hours and an approximately 25% reduction in visual analog scale (VAS) pain score in the post anesthesia care unit and at 6 weeks.4 Although this study provided evidence that there may be reduction in long-term postoperative pain, additional studies are needed to provide evidence that this effect is sustained beyond the 6-week period. We are interested in examining ketamine more closely in spine surgery because this patient population experiences significant postoperative pain that may be difficult to control due to pr