Delirium is a complex neuropsychiatric disorder that has an adverse impact on CNS function. Abnormal fluctuation of melatonin secretion occurs in the postoperative delirium (POD) in elderly patients. POD is strongly associated with early postoperative cognitive dysfunction (POCD). The aim of this study is to test if significant fluctuation of melatonin secretion perioperatively might indicates POCD.

A total of 97 patients, ages 65–80 years, scheduled for major orthopedic surgery or abdominal surgery which was expected to last more than 2 h, were consecutively recruited into this study. Neuropsychological evaluation was performed 1 d before and one week after surgery. Morning urine samples were collected on the day of surgery and on days 1, 2 and 7 after surgery. The 6-SMT/creatinine ratio (M/C ratio) was employed to give an objective estimate of urine 6-SMT concentration. Ultimately, 95 patients completed assessments and were included in the analysis. POCD was found in 30 patients (31.6%) at 1 week after operation. There was significant fluctuation in urinary 6-SMT in 39 of the 95 patients (as evidenced by urinary 6-SMT levels increased or decreased by more than twofold compared with their preoperative baseline). Fluctuations in 6-SMT levels occurred on different days and in some patients lasted for more than 1 d. The incidence of POCD in patients with 6-SMT fluctuation was significantly higher (p < 0.01). The results indicate that in the first week after major noncardiac surgery, POCD occurs in a significant proportion of people, and is linked to fluctuations in endogenous melatonin levels. Measurement of urinary 6-SMT during the perioperative period may assist the diagnosis of POCD.