Comparison Between Low-dose Ketamine Infusion and Intravenous Morphine

Ketamine group: will be administered ketamine in a loading dose of 0.2 mg/kg over 5 min pre incision followed-by an infusion at 0.2 mg/kg/h until the end of surgery.

where normal saline was administered as a loading dose then infused with same rate of another group, throughout the whole surgery.