Predictive value of rest-activity and light exposure patterns for postoperative delirium – exploring potential prevention strategies

• Applicants: Professorin Luísa Klaus Pilz, Ph.D.; Professorin Dr. Claudia Spies
• Subject Area: Anaesthesiology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 563854204

The circadian system generates endogenous 24-hour rhythms that coordinate physiological processes, optimizing the timing of internal functions to the external time. This system operates by entraining internal, self-sustained molecular oscillators to environmental time cues (i.e., zeitgebers), with light-dark-cycles being the most important. Modern lifestyles, characterized by spending most of the time indoors, reduce daytime light exposure while increasing nighttime illumination. This weakens the main zeitgeber, often leading to later chronotypes (with later sleep onsets) and higher circadian misalignment - a discrepancy between internal time and social demands that results in irregular sleep timing. Circadian misalignment reflects disrupted endogenous circadian rhythms and is often estimated using rest-activity rhythms. Actimeters equipped with light sensors enable the long-term tracking of light exposure and rest-activity patterns in real-life settings. The phase angle between circadian phase (dim light melatonin onset, DLMO) and sleep onset time is another metric used to estimate circadian misalignment. Recent, less burdensome methods, such as BodyTime, allow the prediction of DLMO from a single blood sample, making it a practical choice for estimating circadian phase in field studies. Delirium is common in the postoperative course, being defined as post-operative delirium (POD) when it occurs after surgery and anesthesia. POD can lead to long-term cognitive and functional impairments, and contribute to chronic disease. According to the DSM-5, POD’s prevalence is 15%-53% among older individuals. While its etiology is multifactorial, circadian disruption has gained attention recently as a potential risk factor. When compared to patients in the ICU who do not develop delirium, POD patients have disturbed melatonin and cortisol rhythms. Strategies aimed at decreasing circadian disruption during hospitalization, such as light interventions, show encouraging results in reducing the risk for delirium. However, evidence on preoperative circadian misalignment is still limited. Our overarching objective is to assess whether circadian disruption predicts negative postoperative outcomes, especially postoperative delirium. We hypothesize that pre-operative irregular rest-activity patterns, lower light exposure amplitude and an altered phase relationship between circadian phase and sleep onset are associated with POD. Results supporting circadian disruption as a potential risk factor could pave the way for future studies on preventive strategies to protect the aging-brain from perioperative stress. With that in mind, we will i) investigate whether circadian misalignment associates with delirium and ii) pilot-test the feasibility of providing recommendations to decrease circadian disruption before surgery.

• DFG Programme: Research Grants