Postoperative delirium (POD) and postoperative neuropsychological dysfunction are frequently noted in critically ill patients undergoing elective or emergency surgery and treated in the intensive care unit (ICU). Delirium is a serious complication that prolongs hospital stay and contributes to poor outcomes and increased risk of death. The pathomechanisms of delirium are still not very well recognized and there are several theories that seem to explain it. The most important pathomechanisms of delirium are associated with cerebral ischaemia, disorders in acetylcholinergic system, disorders in neuronal plasticity and oxidative stress. Cerebrolysin, a mixture of various peptides obtained from the structural proteins of the pig's brain, possesses strong antioxidative and neuronal protective properties. Cerebrolysin is recommended to treat patients with dementia, after cerebral ischemia and after brain trauma. It has been documented that Cerebrolysin reduces the severity of secondary brain damage after ischemia, improving neuronal plasticity and then cognitive function, and reducing severity of oxidative stress. Based on these properties it can be speculated that Cerebrolysin may reduce the risk of postoperative delirium in patients undergoing elective surgery, which are associated with a high risk of postoperative delirium.

The main hypothesis: Cerebrolysin may be an effective drug to treat dementia and post-ischemic damage. It may improve neuronal plasticity, increase the activity of acetychocholinergic system, and reduces the severity of oxidative stress - all of them are the main factors corresponding to the risk of delirium.

The study will be conducted in accordance with the Declaration of Helsinki, after obtaining approval from the Bioethical Committee and signed informed consent from each patient eligible to participate in the study.

After signing informed consent patients will be randomized using a double-blinded envelope method into two groups: C - control and CER - patients receiving Cerebrolysin at the dose of 50 mL before surgery followed by 50 mL on the morning of days 1,2,3 and 4. The Montreal Cognitive Assessment (MoCA) scale and Mini-Mental State Examination Score (MMSE) will be performed a day before surgery to detect eventual neuropsychological disorders before surgery. The postoperative delirium will be detected with MoCA, MMSE and the Confusion Assessment Method for ICU (CAM-ICU) performed on day 5 after surgery. Additionally, 10 mL of plasma will be collected to assess the following neuro-biomarkers: S100β protein, neurofilament light protein (HNL), Tau protein, ubiquitin carboxy-terminal hydrolase L1 (UCH-L1), and myelin basic protein (MBP). All these biomarkers will be assessed pre-operatively (before Cerebrolysin administration) and on postoperative days 1, 3, and 5. Additionally, routine blood examinations such as arterial blood analysis, blood morphology with NLR and PLR, serum albumin, and CRP will be measured at the same time points.

Inclusion Criteria:

• adult patients aged 18 - 90 years (male and female) undergoing elective coronary artery bypass graft surgery with cardiopulmonary bypass (extracorporeal circulation) not longer than 120 min.
• written informed consent,
• patients without a history of neurology diseases (stroke, cerebral trauma, treated for seizure),
• patients without stenosis of the carotid artery,

Exclusion Criteria:

• any neurological disease,
• intra-operative cardiac arrest,
• perioperative blood transfusion,
• cardiopulmonary bypass (extracorporeal circulation) longer than 120 min,
• any reoperation,
• lack of signed consent for this study,