Neonates born 32 weeks postmenstrual age received either tramadol [ T ] 2 mgkg ( -1 ) or placebo [ P ] 6-hourly for up to 5 days postthoracoabdominal surgery in addition to morphine ( commenced at 20 mcgkg ( -1 ) h ( -1 ) ) and 6-hourly i.v. acetaminophen .