In older patients having surgery, postoperative delirium (an acute disturbance in awareness, attention, or cognition) is common and associated with short-term and long-term morbidity and mortality. The pathophysiology of postoperative delirium is multifactorial - but presumably includes inadequate brain perfusion during surgery caused by low intraoperative blood pressure. Therefore, the investigators aim to determine in a multicenter randomized-controlled trial if targeted intraoperative blood pressure management reduces postoperative delirium. The investigators will test the primary hypothesis that maintaining intraoperative mean arterial pressure at 85 mmHg or higher - compared to at 65 mmHg or higher (routine care) - reduces the incidence of postoperative delirium within the first 3 postoperative days in older patients with arterial hypertension having non-cardiac surgery. The investigators will also assess the duration of postoperative delirium, postoperative complications, and the patients' quality of life. The results of this trial will have a direct impact on guidelines and will help improve medical care for patients and the patients' health. Effective strategies to prevent postoperative delirium are missing. The hypothesis that targeted intraoperative blood pressure management can help reduce postoperative delirium is supported by previous observational studies and interventional trials. This trial is supposed to confirm the causal relationship between intraoperative blood pressure and postoperative delirium and to demonstrate the effectiveness of the therapeutic approach.