Objective: The pathophysiology of postoperative delirium remains poorly understood. The purpose of this study is to examine the relationship between serum cortisol level and the occurrence of early postoperative delirium in patients undergoing coronary artery bypass graft (CABG) surgery.

Methods: A total of 243 patients undergoing elective CABG surgery were enrolled. Postoperative delirium was diagnosed using the Confusion Assessment Method for the Intensive Care Unit from the first postoperative day until hospital discharge. Blood samples were obtained between the hours of 7:00 and 8:00 on the first postoperative day and serum cortisol concentration was measured. Multivariate Logistic regression analyses were performed to identify risk-adjusted factors of postoperative delirium.

Result: Postoperative delirium occurred in 51.0% (124 of 243) patients. Five independent risk factors of postoperative delirium were identified, i.e., increasing age (OR 1.113, 95% CI 1.064-1.165, P < 0.001), a history of diabetes mellitus (OR 2.359, 95% CI 1.205-4.617, P = 0.012), long duration of surgery (OR 1.686, 95% CI 1.195-2.378, P = 0.003), long duration of mechanical ventilation in the ICU (OR 1.070, 95% CI 1.013-1.130, P = 0.015), and higher serum cortisol level (OR 6.285, 95% CI 3.054-12.933, P < 0.001). Comparison between “delirious” and “non-delirious” patients showed that the former group had significantly higher incidence of postoperative complications, longer duration of mechanical ventilation in the ICU, longer duration of postoperative hospital stay, and more medical expanse during hospitalization.

Conclusion: Delirium is a common complication after CABG surgery. Higher serum cortisol level is an independent risk factor of the occurrence of postoperative delirium. Patients who developed delirium had worse outcomes than those who did not.

Key Words: CABG surgery; serum cortisol level; postoperative delirium