Background: Melatonin, a hormone produced in the pineal gland, is involved in circadian rhythms and the sleep-wake cycle. Postoperative delirium is encountered frequently in elderly patients after major surgery; whether changes in the pattern of melatonin secretion are associated is unclear.
Methods: Plasma samples were obtained every 2 hours from 19 patients without delirium and 10 with delirium after major abdominal surgery. Postoperative delirium was determined using the Confusion Assessment Method in the Practice Guideline of the American Psychiatric Association.
Results: All patients without delirium showed nearly identical preoperative and postoperative melatonin secretion for 24 hours, although peak values were significantly lower in patients more than 80 years old (7.2 +/- 2.3 pg/mL) than in patients younger than 80 years (24.4 +/- 4.1 pg/mL, P = 0.022). Patients with delirium showed two different abnormal postoperative patterns: in 5 patients without complications, melatonin levels were lower than preoperative values (11.0 +/- 5.8 versus 6.5 +/- 4.2 pg/mL, P = 0.079); and in 5 patients with complications, melatonin levels were markedly increased (21.1 +/- 4.5 versus 58.8 +/- 12.4 pg/mL, P = 0.043).
Conclusions: Abnormal melatonin secretion may be involved in postoperative sleep disturbances, which triggered delirium in elderly patients.