Melatonin and postoperative delirium: a possible link?

Effects of general versus subarachnoid anaesthesia on circadian melatonin rhythm and postoperative delirium in elderly patients undergoing hip fracture surgery: A prospective cohort clinical trial

BACKGROUND

Circadian rhythm disturbance is common postoperatively in older patients with hip fractures, which may contribute to the development of postoperative delirium (POD). As a reliable biomarker of endogenous circadian rhythms, melatonin regulates the sleep-wake cycle and environmental adaptation, and its secretory rhythm may be modified by anaesthesia and surgery. This study compared the impact of subarachnoid anaesthesia (SA) and general anaesthesia (GA), on the peak of melatonin secretion (primary outcome), the circadian rhythm of melatonin, cortisol and sleep, and the POD incidence (secondary outcome).

METHODS

In this prospective cohort observational study, hip fracture surgery patients were enrolled and assigned to receive either SA or GA. Postoperative plasma melatonin and cortisol levels were dynamically measured every six hours on seven time-points, and the circadian rhythm parameters including mesor, amplitude, and acrophase were calculated. Subjective and objective sleep assessments were performed by sleep diaries and sleep trackers, respectively. The Confusion Assessment Method was used twice daily by a specific geriatrician to screen for POD occurrence.

FINDINGS

In a cohort of 138 patients who underwent hip fracture surgery, the circadian rhythm disruption of the patients in the GA group (n=69) was greater than the SA group (n=69). Compared with SA, GA provided the lower peak concentration, mesor, and amplitude of melatonin secretion on postoperative day 1 (p < 0.05). Patients in the GA group experienced higher awakenings, more sleep deprivation, and poor sleep quality on surgery day (p < 0.05). A proportion of 12 patients in the SA group (17.4%) and 24 patients in the GA group (34.8%) experienced POD (p = 0.020).

INTERPRETATION

These results suggest that SA may be superior to GA in elderly patients undergoing hip fracture surgery as SA is associated with less impairment of the melatonin rhythm and sleep patterns, and fewer POD occurrences.

FUNDING

The study was supported by the National Natural Science Foundation of China (81971012, 81873726, 81901095, 81701052, and 81801070), Key Clinical Projects of Peking University Third Hospital (BYSYZD2019027), and Peking University "Clinical Medicine plus X" Youth Project (PKU2020LCXQ016).

Effects of general versus regional anaesthesia on circadian melatonin rhythm and its association with postoperative delirium in elderly patients undergoing hip fracture surgery: study protocol for a prospective cohort clinical trial

INTRODUCTION

Postoperative delirium (POD) is a common neurological complication after hip fracture surgery and is associated with high morbidity and mortality in elderly patients. Although the specific mechanism of POD remains unclear, circadian rhythm disruptions have recently drawn increased attention. To date, only limited postoperative time points of plasma melatonin level measurements were recorded in previous studies, and such data cannot represent a comprehensive melatonin rhythm. The process of anaesthesia (either general anaesthesia (GA) or regional anaesthesia (RA)) is known to influence the melatonin rhythm. However, how these two anaesthesia methods differently affect the postoperative melatonin rhythm is still unknown. Therefore, we hypothesise that RA may attenuate the disruption of the melatonin rhythm, which might decrease the incidence of POD in elderly patients undergoing hip surgery.

METHODS AND ANALYSIS

In this prospective cohort clinical trial, 138 patients scheduled for hip fracture surgery will be divided into two groups to receive either GA or RA. The primary aim is to compare the circadian rhythm of melatonin secretion between the two groups and explore its association with the incidence of POD.

ETHICS AND DISSEMINATION

The study has been approved by the Medical Science Research Ethics Committees of Beijing Jishuitan Hospital (JLKS201901-04). The results of the study will be published in peer-reviewed international journals.

TRIAL REGISTRATION NUMBER

ChiCTR1900027393.

Melatonin attenuates isoflurane-induced acute memory impairments in aged rats

Melatonin is an endogenous hormone with neuroprotective effects. Melatonin levels in elderly patients are reduced after surgeries that require anaesthesia. Whether reduced melatonin levels are important for postoperative cognitive dysfunction (POCD) remains unclear. Here, we investigated the effects of melatonin on cognitive dysfunctions induced by isoflurane and mechanisms underlying these effects. Seventy-two 20-month-old Sprague-Dawley rats were randomly divided into six groups (n = 12). These groups included M1 and M10 groups that received intraperitoneal melatonin at 1 mg/kg or 10 mg/kg, respectively, and an ISO group that received 4 hr of inhaled 2% isoflurane. They also included M1+ISO and M10+ISO groups that received 1 mg/kg or 10 mg/kg of melatonin plus 4 hr of inhaled 2% isoflurane, respectively, and a control group that received an equal volume of saline. Injections were administered daily for 14 consecutive days. Memory was assessed in the Morris water maze. Plasma and hippocampi were harvested to determine melatonin concentrations and MT1/MT2 receptor expression. Rats treated only with isoflurane showed significantly longer latencies in Morris water maze test trials compared with the control group, with shorter time in the probe trial (p < 0.05). Although plasma melatonin levels and MT2 expression in the hippocampus were significantly decreased, MT1 expression was higher in the isoflurane group than in the control group (p < 0.001). However, these parameters did not significantly vary in animals administered melatonin compared with controls. Isoflurane may induce cognitive dysfunction by influencing melatonin and MT1/MT2 levels. Melatonin can improve cognitive dysfunction by normalizing plasma melatonin and its receptor levels.