The level of acetylcholinesterase is suspected to correlate with postoperative delirium. The investigators therefore score patients once preoperatively and twice postoperatively with the german version of the delirium-score NuDESC (Nursing Delirium Screening Scale) and compare the results with the acetylcholinesterase activity, butyrylcholinesterase activity and the serum anticholinergic activity (SAA) at corresponding time points.