2. Case group: Selected cases divided into the right dexmedetomidine group and control group by computer randomly, 75 patients in each group. Dexmedetomidine group (A group) analgesia pump formula is: fentanyl 100ug + dexmedetomidine 150 ug, with 0.9% saline diluted to 150ml. Control group (group C) postoperative analgesia formula is: fentanyl 150ug, with 0.9% saline diluted to 150ml. Two group with the same anesthesia program. Venous blood serum is taken before surgery, at the before end of surgery and when postoperative analgesia medication runs out (postoperative day 4) to test apolipoprotein E, Amyloid-β1-42, Amyloid-β1-40, N-terminal pro B-type natriuretic peptide.