Incidence of Intensive Care Unit Delirium After Heart Surgery: A Feasibility Study of a Forest Environment Intervention

BACKGROUND: Postoperative delirium is a serious complication in intensive care units (ICUs), particularly following cardiac surgery. It is associated with circadian rhythm disruption, sleep disturbances and adverse outcomes. ICU environments often lack natural time cues, which may exacerbate circadian misalignment and increase delirium risk. AIM: The primary aim of the study was the evaluation of the implementation of two chronotherapeutic ICU interventions regarding recruitment, implementability and safety. Its secondary aim was to descriptively assess postoperative delirium across intervention groups. STUDY DESIGN: This randomized feasibility study was conducted in a tertiary cardiac surgery ICU in Austria. Adult patients undergoing elective cardiac surgery were allocated to one of three groups: (1) forest environment, (2) light exposure or (3) standard ICU care. Interventions were applied for 12 h daily. Delirium was assessed at three postoperative time points using the confusion assessment method for the ICU (CAM-ICU) and intensive care delirium screening checklist (ICDSC). RESULTS: This study was conducted between March 2020 and 2025. Seventy-seven patients were enrolled, and 64 remained in the final analytical cohort. Interventions were delivered within routine care. Patients and ICU staff did not report intervention-related concerns. Implementation challenges included ICU restructuring, patient transfers due to COVID-19 and deviations from randomized allocation because of operational constraints. No intervention-related adverse events occurred. Delirium assessments were limited at several time points because of sedation, early ICU discharge or transfer. Across all groups, postoperative delirium was detected in 5 of 130 CAM-ICU completed assessments (3.8%) and 8 of 115 ICDSC completed assessments (6.9%), precluding inferential group comparisons. CONCLUSIONS: Chronotherapeutic environmental interventions were feasible and safe in ICU care. Feasibility results highlighted challenges related to ICU logistics, sedation-related assessment limitations and pandemic-related disruptions. The unexpectedly low delirium incidence limited conclusions regarding intervention efficacy. Future trials should include larger high-risk populations and prospectively defined feasibility outcomes. RELEVANCE TO CLINICAL PRACTICE: Optimized ICU environments, including noise reduction and light management, may support delirium prevention. Chronotherapeutic environmental interventions are feasible additions to routine ICU care.