CIRCA-MED WP1 & WP3 - Circadian Rhythms in ICU Patients

Retrospective Characterization of Circadian Rhythms Using Vital Signs and Other Routine Data From Patients in the Intensive Care Unit

The goal of this retrospective exploratory study is to examine how the body's natural day-and-night rhythms and oscillatory patterns behave in people who were treated in the Intensive Care Unit (ICU). The study uses routine clinical data that were already collected during and after the ICU stay, including post-discharge follow-up measurements (where available), such as heart rate, temperature, blood pressure, blood sugar, and insulin. The researchers want to learn whether these measurements show daily patterns and whether patients can be grouped based on their oscillatory profiles. The study also examines whether certain clinical factors such as illness severity scores, sedation levels, organ support treatments, or medications are associated with changes in these oscillatory rhythms. The team will explore whether conditions that can develop during or after critical illness, such as delirium, muscle weakness, or Post-Intensive Care Syndrome (PICS), are linked to disturbed physiological rhythms. Another goal is to test whether it is technically possible to show a patient's rhythm profile in real time using routine data from the ICU information system, evaluated retrospectively. Digital tools called "Chrono-Apps" will be developed to display rhythmic information and may help clinicians adjust lighting to patient needs.

The investigators will retrospectively analyze periodic oscillations in clinical data, such as heart rate, temperature, blood glucose, insulin, or blood pressure, to identify parameters suitable for characterizing the physiological rhythms in hospitalized Intensive Care Unit (ICU) patients. While these measurements typically show regular daily changes, also called oscillatory patterns, critical illness, continuous monitoring, and frequent medical interventions can disrupt them. The study will investigate whether these patterns can be used to group patients into distinct temporal or rhythmic profiles. The study will also examine whether certain clinical factors are linked to functioning or disrupted oscillatory patterns. These factors include illness severity scores, sedation levels, organ support treatments, and medications. Additionally, the researchers will explore whether temporal disruption is associated with key ICU complications, including delirium, ICU-acquired muscle weakness, and Post-Intensive Care Syndrome (PICS). Finally, in a small cohort of ICU patients, the investigators will test personalized lighting regimens adapted to individual chronotypes. This phase of the study aims to assess the robustness of routine clinical data for tailoring light exposure, validate a circadian entrainment algorithm, and evaluate potential sources of bias. Real-time analyses of clinical data will be visualized as rhythm profiles via digital "Chrono-Apps" integrated into the electronic patient record. These visualizations will support the day-to-day implementation of personalized lighting regimens that adapt dynamically to each patient's current rhythm status and clinical condition.

Inclusion Criteria:

Primary Retrospective Cohort:

• Admitted to and treated in a participating Intensive Care Unit (ICU) between 2017 and 2024
• Minimum ICU length of stay of 3 days (≥ 72 hours)
• Age ≥ 18 years at the time of ICU admission
• All genders (male, female, diverse)

Cohorts from previous studies:

• Prior enrollment in one of the designated parent study protocols
• Availability of supplementary biological or metabolic data (e.g., clock gene expression, melatonin levels) suitable for exploratory association analyses

Exclusion Criteria:

• None