The efficacy and safety of ramelteon in prevention of postoperative delirium in the elderly

INTERVENTION: Control group are received placebo capsule (lactose) 8mg before two hours at sleep time every night at least two weeks before operation day. Ramelteon 4mg group are received Ramelteon capsule 4mg before two hours at sleep time every night at least two weeks before operation day. Ramelteon 8mg group are received Ramelteon capsule 8mg before two hours at sleep time every night at least two weeks before operation day. CONDITION: postoperative delirium PRIMARY OUTCOME: The primary outcome was the occurrence of delirium as determined by Confusion Assessment Methods‐ICU (CAM‐ICU) criteria at day 1,2,3,and 7 after operation. SECONDARY OUTCOME: The secondary outcome was the degree of severity of delirium as determined by Method Delirium Assessment Scale (MDAS); criteria if postoperative delirium occurs. INCLUSION CRITERIA: Patients aged over 65 years scheduled for operation at Kobe University Hospital Hepato‐biliary‐pancreatic surgery.