Routine ICU data offers valuable insights into daily physiological rhythms. While traditional methods assume these cycles maintain fixed periods and amplitudes, their inherent variability requires dynamic estimation of instantaneous trends. Wavelet transform effectively resolves circadian oscillations, especially for frequently measured vital parameters. We present novel extensions to the Continuous Wavelet Transform (CWT) power spectral analysis to better detect and segment subtle temporal patterns. Using this approach, we uncover hidden circadian patterns in cardiovascular vitals such as Heart Rate (HR) and Mean Blood Pressure (MBP) measured over five days in a retrospective cohort of 855 ICU patients. By quantifying non-stationary rhythms, we identified diurnal and semi-diurnal oscillations varying in period and power according to delirium and deep sedation. Notably, HR exhibits a clear diurnal and semi-diurnal rhythm when delirium is absent. Overall, our framework supports the CWT as a powerful tool for analyzing complex physiological signals, particularly vital signs. Crucially, our findings suggest that cardiovascular rhythm disruption can be associated with ICU-related delirium and deep sedation.

J.S., E.S.B. and E.G. report no conflict of interest with respect to the study. A.E. declares that his institution received payments or honoraria for lectures and expert testimony from Gilead Sciences GmbH and Draeger Medical Deutschland GmbH. He holds shares of BioNTech and Novavax (less than 5000 Euros). A.E. declares to be a member of the German Society of Anaesthesiology and Intensive Care Medicine (DGAI) and participates in the DGAI Round Table on Tele ICU. Additionally, A.E. collaborates in the section on Metabolism and Nutrition of the German Interdisciplinary Association for Intensive and Emergency Medicine (DIVI). He holds memberships in several other organizations, including the German Sepsis Society (DSG), the European Society of Intensive Care Medicine (ESICM), the European Society of Anaesthesiology and Intensive Care (ESAIC), the German Society for Nutritional Medicine (DGEM), and the European Society for Clinical Nutrition and Metabolism (ESPEN), although he is not actively involved in committee work in these organizations. S.K.P. has no conflicts of interest with respect to the study. Outside the submitted work, she has participated in several Data Safety Monitoring Board meetings that are completely unrelated to this work and the co authors. C.S. reports grants from the German Research Society (Deutsche Forschungsgemeinschaft), Einstein Foundation Berlin, German Federal Joint Committee (Gemeinsamer Bundesausschuss G BA), Inner University Grants, Stifterverband (non profit society promoting science and education), European Society of Anaesthesiology and Intensive Care, German Federal Ministry for Economic Affairs and Energy (BMWE), Georg Thieme Verlag, Dr. F. Koehler Chemie GmbH, Sintetica GmbH, Stifterverband fuer die Deutsche Wissenschaft e.V. (Medtronic and Teladoc Health), Philips Electronics Nederland BV, German Federal Ministry of Research, Technology and Space (BMFTR), Robert Koch Institute, a Federal Institute within the portfolio of the German Federal Ministry of Health, and the European Commission Horizon Europe during the conduct of the study. In addition, C.S. has different patents and an unpaid leadership or fiduciary role in the German Research Foundation (Deutsche Forschungsgemeinschaft), German National Academy of Sciences Leopoldina (Deutsche Akademie der Naturforscher Leopoldina e. V.), Berlin Medical Society (Berliner Medizinische Gesellschaft), ESICM (European Society of Intensive Care Medicine), ESAIC (European Society of Anaesthesiology and Intensive Care), German Society of Anaesthesiology and Intensive Care Medicine (DGAI), German Interdisciplinary Association for Intensive Care and Emergency Medicine (DIVI) and German Sepsis Foundation (Deutsche Sepsis Stiftung). C.S. has participated on the Data Safety Monitoring Board or Advisory Board of Takeda Pharmaceutical Company Limited, Lynx Health Science GmbH and Mundipharma. F.B. reports grants from the German Research Society (Deutsche Forschungsgemeinschaft), Berlin Institute of Health, Berlin University Alliance, Brandenburg Medical School Theodor Fontane, Charite Foundation, Einstein Foundation, European Commission, Federal office for Information Security (BSI), Fresenius Foundation, German Federal Ministry of Education and Research (BMBF), German Federal Ministry of Health (BMG), German Federal Ministry of Research, Technology and Space (BMFTR), German Portal for Medical Research Data (FDPG), Hans Boeckler Foundation, Honda Research Foundation, Joint Federal Committee, Masimo and Philips. Outside the submitted work, F.B. reports royalty payment from Elsevier publishing and has also received financial support from Pfizer for presentations. F.B. reports support for attending meetings from the Association of German Anesthetists, Bavarian Academy of Science and Humanities, German Society of Anesthesiology and Intensive Care Medicine, Masimo and Robert Koch Institute. S.D.B declares that he is a salaried employee at Pfizer Pharma GmbH and his employment has no connection to this work. Outside the submitted work, S.D.B reports financial support from DGPharMed e.V. for a lecture. In addition, he holds shares of Pfizer Pharma GmbH unrelated to this work.

This research was initially supported by the Will Foundation (AnaeVPostDelir: 137017) and subsequently funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation), Project ID: 541063275, TRR 418.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The study was approved by the ethics committee of the Charite Universitaetsmedizin Berlin and has been registered in the German Clinical Trials Register (DRKS00036535). The requirement for informed consent was waived due to the retrospective design and use of pseudonymized data.

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

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I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

The data that supports the findings of this study is restricted by ethical limitations and so is not publicly available. Any reasonable request should be made to any of the corresponding authors of this paper.