Moreover, there is a considerable discrepancy between studies on the incidence and risk factors of delirium among cardiac surgery patients.The first potential reason for this observation is retrospective design of some studies, secondly, the modest number of participants in numerous prospective studies which does not provide strong statistical power to select patients with delirium and detect risk factors of this complication. Unfortunately, reports with a more considerable number of patients often have methodological limitations. Additionally, in previous studies authors usually analyzed pre- and intraoperative variables ignoring potential postoperative risk factors of delirium. Finally, some variables which seem to have a crucial role in aetiology of delirium after cardiac surgery, particularly perioperative hypoxia, anaemia, and preoperative psychiatric disorders like depression and cognitive impairment, have not been properly investigated to date.