Background: This study aims to investigate the association between postoperative delirium and cognitive dysfunction after cardiac surgery and to determine the effects of postoperative delirium on postoperative cognitive dysfunction and sleep disturbances in the long-term.

Methods: Among 285 patients who underwent open cardiac surgery between May 2010 and July 2011, 51 patients who met the inclusion criteria were enrolled in the study. Twenty-six patients (group 1) who developed postoperative delirium were compared with 25 patients (group 2) without delirium. Cognitive function was assessed by mini-mental state examination (MMSE) test at pre-discharge, six and 12 months after surgery. Involving into the working life was questioned in both groups at the 12 months after surgery. Functional ability was assessed by the assistance need for instrumental activities of daily living (IADL), whereas sleep disturbances were assessed by the Pittsburgh sleep quality index (PSQI).

Results: Patients in group 1 had lower mean MMSE scores compared to patients in group 2 before hospital discharge (26.0 versus 28.6, p<0.001). The mean MMSE scores were significantly lower in group 1 at six and 12 months after surgery (26.7 versus 29.2 and 28.0 versus 29, p<0.001, respectively). Sleep disturbances were also significantly higher at 12 months after surgery in group 1, compared to group 2 (73.1% versus 32.0%, p<0.001).

Conclusion: Postoperative delirium after cardiac surgery is a risk factor for prolonged postoperative cognitive dysfunction. It is also associated with a significant decline in cognitive ability and sleep disturbances during the first year after cardiac surgery.

Keywords : Cardiac surgery; cognitive dysfunction; delirium