This study is aimed at finding a correlation between postoperative delirium occurrence, severity and duration after cardiac surgery and the level of brain-derived neurotrophic factor (BDNF) in plasma as a marker of brain injury induced by cardio-pulmonary by-pass and its association with genetic predisposition in patients undergoing coronary artery bypass grafting (CABG) carrying BDNF gene polymorphism (Val66Met).

Inclusion criteria include:

1. Age > 18 years.
2. Planned coronary artery bypass grafting (CABG) procedure with the use of cardiopulmonary by-pass (CPB).
3. Ability to understand and sign an informed consent form.

Exclusion criteria include:

1. Emergency surgery.
2. Previous known cognitive disorders: Mini Mental State Examination (MMSE) score <15.
3. Baseline delirium (positive CAM test prior to surgery).
4. Diagnosis of psychiatric syndromes in the past - i.e. depression, dementia, psychosis or schizophrenia.
5. Inability to understand Polish language.
6. Inability to give and sign informed consent due to auditory or visual dysfunction.

A prospective observational cohort study will recruit 200 patients scheduled for planned coronary artery bypass grafting (CABG), with the use of cardio-pulmonary by-pass who will be operated at the Cardiac Surgery Department of the Pomeranian Medical University in Szczecin. The Cardiac Surgery Department of Pomeranian Medical University has a volume of 900-1100 operations per year, 70% being CABG (approx. 700 CABG operations per year).