Effect of a modified ICU environment on circadian cortisol rhythms in critically ill patients

Circadian cortisol rhythms are essential for vital physiological processes and are often disrupted during critical illness. It remains unclear whether ICU room modifications, including dynamic light therapy, affect cortisol rhythms. In this secondary endpoint analysis of the VITALITY trial, we investigated the effect of a modified ICU environment on cortisol rhythms in mechanically ventilated patients. Modifications included simulated natural 24-hour light–dark cycles, noise reduction, and environmental design adaptations. Serum cortisol was measured every 4 hours over up to three 24-hour periods (SCAP-A, -B, -C) in patients treated in modified (n = 36) versus standard (n = 37) ICU rooms. Cortisol rhythms were modeled using Cosinor analysis. Cortisol levels and rhythm parameters were analyzed using non-parametric analysis for longitudinal data. Cortisol levels did not differ between groups (SCAP-A: p = 0.50; SCAP-B: p = 0.68; SCAP-C: p = 0.83). Circadian cortisol rhythms also showed no significant differences. Time of lowest cortisol value (nadir) was distributed across the entire 24-hour period in both groups indicating high interindividual variability in circadian cortisol rhythms. Our findings suggest that cortisol rhythms are strongly altered in critical illness and may not be influenced by modified rooms including dynamic lighting alone. Given the heterogeneity and sample size, small effects cannot be excluded. Trial registration: ClinicalTrials.gov NCT02143661.