Postoperative cognitive dysfunction (POCD) and postoperative delirium occurs mainly in aged patients. POCD and POD may increase the mortality and morbidity. However, the mechanism of POCD is not clear yet and no effective therapy method was proved. According to previous study, the neuroinflammation is the main reason both for POCD and POD. Minocycline is a tetracycline derivative. Due to it's lipophilic structure, it is easy to pass through blood brain barrier and attenuate neuroinflammation. It's neuroprotective effects has been proven in many experimental animal models such as Alzheimer's disease, Huntington's disease and Parkinson's syndrome. In present study, the investigators hypothesized that minocycline would attenuate the incidence of POCD and POD in the aged patients.