Remimazolam is an ultra-short acting benzodiazepine agonist which is used widely for general anesthesia and sedation. Remimazolam has several advantages. Remimazolam is rapidly metabolized by tissue esterase that it does not accumulate even after infusion for long periods of time. The presence of reversal agents (flumazenil) is also advantageous. Also, hemodynamic stability compared to propofol gives clinicians preference to use for geriatric anesthesia. However, the study on the effect of remimazolam compared to propofol on postoperative delirium have not been carried out. The purpose of the study is to compare the incidence of postoperative delirium and recovery profile in elderly patients undergoing orthopedic surgery using either remimazolam or propofol.

Inclusion Criteria:

• elderly patients undergoing hip or knee arthroplasty under general anesthesia.
• body mass index >30 kg/m2

Exclusion Criteria:

• moderate to severe liver dysfunction
• moderate to severe renal dysfunction
• unable to extubate in the operation room after operation
• benzodiazepine dependence
• sensitivity to anesthetic drugs used for study (Benzodiazepines, Propofol, Remifentanil, Fentanyl citrate, Rocuronium bromide, Sugammadex, Flumazenil)
• acute angle glaucoma
• received (benzodiazepine, antianxiety drugs, antidepressant, antipsychotic drugs) within 24 hours.
• acute psychotic depression
• history stroke or cerebrovascular disease