Pregabalin and Hypotensive Anesthesia

INTERVENTION: general anesthesia only Pregabalin group CONDITION: ; Nervous System Diseases ; Surgery ; spine surgery Nervous System Diseases spine surgery Surgery PRIMARY OUTCOME: Intraoperative consumption of nitroglycerin to maintain the target MAP 55‐ 65 mmHg. SECONDARY OUTCOME: estimated blood loss end‐tidal isoflurane concentration Frequency of adverse effects as dizziness, headache, nausea and vomiting, or pruritus. heart rate (HR) and invasive MAP Peak and plateau airway pressures Postoperative pain (by VAS 0‐10 scale) Sedation (by Ramsay sedation scale) Surgeon satisfaction about the field (scale 0‐5) The number of transfused blood unites The time to the first request of analgesia. The total morphine consumption INCLUSION CRITERIA: ‐ aged 18¿55 years, ‐ American Society of Anesthesiologists (ASA) score I‐II ‐ admitted to undergo elective lumbar discectomy or spinal fixation surgery under general anesthesia