Delirium is common in critically ill patients and is linked to poor outcomes like prolonged hospital stays and cognitive impairment. Subsyndromal delirium (SSD) is an intermediate state between no delirium and full delirium, involving cognitive and behavioural abnormalities without meeting DSM-5 criteria for delirium. SSD affects about one-third of ICU patients and may progress to delirium, but its clinical significance remains unclear due to varying incidence rates and inconsistent associations with adverse outcomes. While ICU delirium has been well studied, SSD is less defined, with limited research on its risk factors and effects.
A recent study aimed to identify SSD risk factors, its progression to delirium, and its impact on patient outcomes, with the goal of improving ICU care through targeted interventions.
The study screened ICU patients using the Intensive Care Delirium Screening Checklist (ICDSC), excluding those with primary neurologic diagnoses or persistent coma. SSD was defined by an ICDSC score of 1–3. The primary outcomes were identifying risk factors for SSD progression and its association with hospital mortality. Secondary outcomes included ICU mortality and length of stay.
Among 1,572 patients, 31% had SSD without delirium, 11.5% had SSD that progressed to delirium, 11.1% had delirium without prior SSD, and 35.8% had no delirium. Risk factors for SSD onset included female sex, higher APACHE IV score, and medical/emergency surgery admissions. SSD progression was associated with higher APACHE IV score, medical/emergency surgery admissions, metabolic acidosis, and early morphine use. SSD patients had lower hospital mortality than delirium patients but no significant difference compared to non-delirious patients. ICU stays for SSD patients were shorter than for delirium patients but longer than for non-delirious patients.
This study found that over half of ICU patients experienced delirium symptoms, confirming SSD as a clinically significant intermediate state between no delirium and full delirium. While SSD without progression was not linked to higher hospital mortality than non-delirious patients, it was associated with increased disease severity. SSD patients had shorter ICU stays than those with delirium, highlighting the importance of early identification and management.
Non-pharmacological interventions, such as early mobilisation, may help prevent SSD progression, though pharmacological strategies require further study.
Clinically, SSD represents a precursor to delirium, and early recognition could enable preventive interventions. Future research should focus on SSD mechanisms and its role in patient outcomes.
This study highlights the clinical importance of SSD in ICU patients, confirming it as an intermediate prognostic state between no delirium and full delirium. Identified risk factors for SSD onset and progression to delirium may help guide early intervention strategies.
Source: Journal of Critical Care
Image Credit: iStock
References:
Smit L et al. (2025) Risk factors for transitions and outcomes of subsyndromal delirium in the ICU: Post-hoc analysis of a prospective multicenter cohort study. Journal of Critical Care. 88:155041.
