Nalbuphine Versus Tramadol on Post Operative Analgesia in Abdominal Surgery on Pediatric Cancer Patient

this group will a single dose of nalbuphine (0.2 mg/kg) immediately after surgery to be repeated every 8 hours for the duration of the study (72 hours)

this group will receive a single dose of tramadol (2 mg/kg) immediately after surgery to be repeated every 8 hours for the duration of the study (72 hours).