Relationship among melatonin, postoperative delirium, and postoperative cognitive dysfunction.

BACKGROUND

Postoperative delirium (POD) and postoperative cognitive dysfunction (POCD) are the most common central nervous system dysfunctions during the perioperative period. Melatonin protects nerve cells and impacts cognitive functioning in patients after surgery.

METHODS

A total of 120 patients undergoing elective non-cardiac surgery were evaluated with the confusion assessment method (CAM) for diagnosis of POD on the day before and the 1st, 2nd, 3rd, and 7th day after surgery. Also, a neuropsychological test for the diagnosis of POCD was performed on the day before and 1 week after surgery. Patients' urine was collected to examine the concentration of 6-sulfatoxymelatonin (6-SMT), the metabolite of melatonin, with the enzyme-linked immunosorbent assay method. Meanwhile, urine creatinine values were examined to calculate the 6-SMT/creatinine ratio (M/C).

RESULTS

The incidence rates of POD and POCD were 7% and 44%, respectively. There were no statistically differences for the M/C on the 1st, 2nd, 3rd, and 7th day after surgery between the POD and the non-POD groups (P>0.05). However, there were statistically significant differences (P<0.05) in the rates of M/C change [(preoperative value-postoperative value)/(postoperative value) ×100%] on the 1st and 7th day after surgery between both groups. Patients were divided into Group I1 (≥100%) and Group II1 (<100%) based on the M/C rate changes on the 1st day, Group I7 (≥200%) and Group II7 (<200%) based on the M/C rate changes on the 7th day, and Group Iw (≥100%) and Group IIw (<100%) based on the M/C rate changes during the 1st week after surgery. The incidence rates of POD for Group I1 and Group II1 were 21.1% and 3.7%, respectively; for Group I7 and Group II7 were 50% and 1.1%, respectively; for Group Iw and Group IIw were 17.2% and 2.8%, respectively. For 7 patients with POD had POCD, the occurrence of POCD was related to POD (P<0.05).

CONCLUSIONS

Increased melatonin after surgery may be a risk factor for POD. There may be no correlation between melatonin and POCD. POD may be a risk factor of POCD.