A consecutive series of patients scheduled for elective cardiac surgery is included in the study. Delirium screening is performed using Intensive Care Delirium Screening Checklist. Preoperative cognitive state is evaluated with Mini-Mental State Examination. Information of possible risk factors is collected from patient's history and chart. The Snoring, Tiredness, Observed apnea, high blood Pressure-Body mass index (BMI), Age, Neck circumference and Gender questionnaire (STOP-BANG questionnaire) is used for obstructive sleep apnea screening.