Risk factors for transitions and outcomes of subsyndromal delirium in the ICU: Post-hoc analysis of a prospective multicenter cohort study

Purpose: Identify risk factors for progression to delirium and outcomes of subsyndromal delirium (SSD) in critically ill adults. Methods: Multicenter prospective study screening patients with the Intensive Care Delirium Screening Checklist (ICDSC), excluding those with primary neurologic diagnosis or persistent coma. SSD was defined as an ICDSC score 1–3. Main outcomes were risk factors for SSD progression and association with hospital mortality. Secondary outcomes included ICU mortality and length of stay. Results: Among 1572 patients, 562 (35.8 %) had no delirium, 488 (31 %) SSD without delirium, 180 (11.5 %) SSD progressing to delirium and 174 (11.1 %) delirium without prior SSD. For 168 (10.7 %) delirium status was unknown. SSD onset risk factors were female sex, higher APACHE IV score, and medical /emergency surgery admissions. SSD progression risk factors included higher APACHE IV score, medical/emergency surgery admissions, metabolic acidosis and morphine dosage in the first 24 h. SSD patients had lower hospital mortality than delirium patients (OR 0.57, 95 %CI 0.36 to 0.90), but no significant difference compared to non-delirious patients (OR 1.30, 95 %CI 0.69 to 2.42). SSD patients had shorter ICU stays than delirium patients but longer than non-delirious patients. Conclusions: This study identified risk profiles and validated SSD as an intermediate prognostic condition, supporting early interventions to prevent delirium-associated harms. Trial registration: ClinicalTrials.gov Identifier NCT01952899 (registered September 30, 2013).