Mini-mental state examination (MMSE) scale was used to assess the cognitive ability of the patients,[12 (link)] which mainly covered orientation, attention, calculation, short-term memory, language ability, recall ability, visual-spatial ability, and other aspects. The total score of this scale was 30 points, of which 27 to 30 points was normal and <27 points could be judged as POCD. At 1 day, 3 days and 7 days after surgery, each patient was scored by the medical staff using the MMSE scale Patients were included in the control group with all scores ≥ 27 at each time point, while the others with a score < 27 at any point in time were included in POCD group.