Abnormal pain sensitivity is a phenomenon associated with thelong term use of opioids medication. This phenomenon likely resultsfrom changes in NMDA receptors in the dorsal horn of the spinal cord.Although opioids are unsurpassed analgesics for surgery, they also inducean N-methyl-d-aspartate-dependent enhancement of postoperativehyperalgesia. Because nitrous oxide (N2O) has anti-N-methyl-d-aspartateproperties, the purpose of this essay was to demonstrate nitrous oxideability to prevent such an opioid-induced hyperalgesia .