Characterization of 24-Hour Rhythms in Vital Signs in Intensive Care Populations: A Scoping Review.

Circadian rhythms in intensive care unit (ICU) patients are vulnerable to disruption, which may contribute to adverse clinical outcomes. Continuously monitored vital signs offer a unique opportunity to assess 24-hour rhythms in real-world ICU settings. The aim of this scoping review is to systematically map methodological approaches used to characterize 24-hour rhythms in vital signs in ICU populations and to summarize reported associations with patient characteristics, clinical outcomes, or interventions. A systematic literature search was conducted to identify studies that assessed 24-hour rhythms in routinely collected vital signs in adult, pediatric and neonatal ICU patients published between January 2015 and December 2025. Thirty-five studies comprising nearly 288 000 patients were included, with most studies conducted in adult ICUs (n = 32), 3 in neonatal ICUs, and none in pediatric ICUs. Substantial heterogeneity existed in preprocessing strategies, assessment windows, analytical methods, and derived rhythmicity metrics that were used to determine 24-hour variation, as well as in the level of detail with which these were reported. Cosinor analysis was the most frequently used method to characterize rhythmicity, followed by day-night comparisons, and max-min approaches. Across studies, rhythmicity analyses revealed that 24-hour rhythms in vital signs were detectable in ICU patients, although methodological heterogeneity and lack of detail on analytical decisions limit evidence synthesis. In addition, the direction and magnitude of associations between rhythmic properties (such as amplitude or acrophase) and mortality and other clinically relevant outcomes varied considerably among studies. While most, though not all, studies reported that higher amplitudes were associated with mortality, it remains unclear whether this reflects circadian physiology rather than clinical instability. Harmonization of reporting practices and the development of a core outcome set on circadian parameters derived from vital signs in critical care contexts will help to guide future research in this burgeoning field.