A Comparison of Intra-op Ketamine vs Placebo in Patients Having Spinal Fusion

Postoperative pain is severe after major spine surgery. Opioids such as morphine and hydromorphone are routinely used for postoperative pain control. These drugs have significant side effects, most importantly respiratory depression, nausea, constipation and tolerance. Moreover, many spine surgery patients have used opioid pain medication for back pain long term, leading to pre-surgical opioid tolerance and increased postoperative pain. This has led to a search for adjuvant medications to reduce the use of opioids and reduce opioid mediated side effects and tolerance. Ketamine is an intravenous anesthetic with analgesic properties in subanesthetic doses. Ketamine is a noncompetitive antagonist of N-methyl-D-aspartate (NMDA) receptors. NMDA receptors are involved in central pain sensitization via wind-up phenomenon and altered pain memory, a process which can be blocked by ketamine. NMDA receptor antagonists may prevent the development of tolerance to opioids and hyperalgesia. Ketamine has been safely used to decrease pain in numerous studies. Ketamine can also act as an antidepressant with hours of administration. Ketamine has rapid brain uptake and subsequent re-distribution with a distribution half-life of 10-15 minutes and an elimination half-life of 2 hours. Ketamine does not cause respiratory depression.