Incidence and Risk Factors of Delirium and Subsyndromal Delirium in Intensive Care Unit Patients: An Observational Study

ABSTRACT Background Delirium is common in intensive care unit (ICU) patients and is associated with adverse outcomes. Subsyndromal delirium (SSD) represents a milder form of this spectrum, which frequently goes unnoticed. It is important to clarify its incidence and risk factors to guide early detection and prevention. Aim To determine the incidence and risk factors of delirium and SSD in ICU patients. Study Design This prospective observational study was conducted in a medical‐surgical ICU in Izmir/Turkiye. Adult patients ≥ 18 years and admitted for ≥ 24 h were assessed twice daily using the Intensive Care Delirium Screening Checklist (ICDSC) and the Richmond Agitation‐Sedation Scale (RASS) to identify delirium and SSD. Demographic and clinical data were recorded for potential risk factors, and associations with delirium and SSD were analysed using univariate tests and multinomial logistic regression. Results Among 233 patients, delirium occurred in 37.8% and SSD in 33.0%. Significant risk factors for both conditions were higher pain score (delirium: OR = 2.35, 95% CI: 1.59–3.46; SSD: OR = 2.83, 95% CI: 1.80–4.46), midazolam use (delirium: OR = 7.93, 95% CI: 1.97–17.64; SSD: OR = 4.12, 95% CI: 1.82–8.55) and physical restraint (delirium: OR = 1.60, 95% CI: 1.22–3.83; SSD: OR = 2.02, 95% CI: 1.86–4.72). Mechanical ventilation (OR = 1.67, 95% CI: 1.13–3.69) and vasopressor use (OR = 0.83, 95% CI: 1.06–2.14) were associated only with delirium, while longer ICU stay (OR = 1.55, 95% CI: 1.12–3.17) was associated only with SSD. Conclusion SSD is a frequent and early‐occurring condition in ICU patients, with both shared and unique risk factors compared to fully manifest delirium, underscoring the need for vigilant monitoring and timely intervention. Relevance to Clinical Practice Implementing routine screening and addressing modifiable risk factors may prevent SSD progression to delirium and enhance ICU patient outcomes.