Comparative Study of Opioid-Free Anesthesia Versus Opioid Anesthesia in Patients Undergoing Laparoscopic Cholecystectomy

patients will receive : nalbuphine administered at a dose of 0.2 mg / kg IV bolus dose before induction and intermittent doses of 0.5 mg/kg if MAP and HR greater than 20% of the base line value.

patients will receive : Dexmedetomidine infusion at rate of 0.5mcg/kg/h initiated 10 min before induction and ketamine iv bolus dose of 0.35 mg/kg and Lidocaine iv bolus dose of 1mg/kg administrated before skin incision.