Perioperative Electroencephalography Characteristics of Postoperative Delirium in Elderly

The investigators aim to identify preoperative Electroencephalogram (EEG) markers indicating patients at risk to develop postoperative delirium (POD), so that the anesthetist may adjust medications and dosages in order to avoid POD. Second, the investigators aim to specify intraoperative EEG signatures and EEG states that are related to POD and long-term cognitive dysfunction, again to enable physicians to adapt their procedure. Third, the investigators aim to identify EEG signatures during stay in the recovery room that is directly related to POD, and may therefore be used as diagnostic tool, as well as a predictor for the development of long-term cognitive deficits (POCD).