Peroperative opioids are known to induce N-Methyl-D-Aspartate dependent enhancement of postoperative hyperalgesia. For patients with current opioid treatment, these phenomena could be exagerated and could produce greater postoperative opioid consumption and higher pain score. Since Nitrous oxide has anti- N-Methyl-D-Aspartate properties, the aim of this study was to evaluate, in patients with current opioid treatment, the effects of peroperative Nitous oxide on postoperative opioid consumption and pain score, after vertebroplasty.