Previous studies have revealed age as a well-established predictor for POD with no certain mechanisms [16, 17]. In this present study, the patients who underwent POD also had a higher age than those without POD. However, the final multivariate analysis did not indicate age as a predicator as expected, which might be explained by the small age range or different operation types of the enrolled participants. Preoperative cognitive function decline is considered as a risk factor for postoperative cognitive problems and later life equality . Our results from univariate analysis instead of multivariate analysis also showed a close association between preoperative MMSE score and POD. Previous studies have also indicated that longer operation and anesthesia time predict delirium after cardiac surgery due to increased cytokines release and operation complexity , which was not quite in accordance with our results.