Dexmedetomidine Dosage for Postoperative Delirium and Cognitive Function in Elderly TKA Patients

Inclusion Criteria: * Patients with Severe chronic knee osteoarthritis inducing limitation of movement and required knee replacements; * Patients of American Society of Anesthesiologists Classification grades II-III; * Patients free of exclusion criteria. Exclusion Criteria: * Patients of American Society of Anesthesiologists Classification grade \>III; * Patients show a high risk for getting Post Operative Delirium or have severe cognitive dysfunction; * Patients had a history of uncompensated cardiac, renal, or hepatic diseases; * Patients had uncontrolled diabetes mellitus or hypertension; * Patients had other causes for limited movement; * Patients had autoimmune disease, coagulopathy, severe anemia with a hemoglobin concentration of \<7 g%; * Patients had local bone disorders that may prevent prosthesis stability; * Patients had allergies or contraindications to the study drugs.