Frequency and risk factors for subsyndromal delirium in an intensive care unit.

OBJECTIVE: Delirium and subsyndromal delirium in critically ill patients are important determinants of long-term functional disability and cognitive impairment. However, few outcome studies on sub-syndromal delirium have been reported. Thus, this study aimed to evaluate the incidence of delirium and sub-syndromal delirium as well as the risk factors and progression to delirium.

DESIGN: A prospective cohort study.

SETTING: Six bed medical and surgical intensive care unit in Otsu Municipal Hospital in Japan.

METHODS: Delirium and sub syndromal delirium were evaluated using the Intensive Care Delirium Screening Checklist scores and the demographic data of the patients recorded. Statistical analyses were conducted using the Mann-Whitney U test and chi-square test for comparison. We also compared groups using multivariate analyses.

RESULTS: Of the 380 patients who were screened, 15.8% and 33.9% had delirium or sub syndromal delirium, respectively and 9.5% of patients progressed from a state of sub syndromal delirium to delirium. Older age, predisposing cognitive impairment, blood transfusion, higher Acute Physiology and Chronic Health Evaluation II (APACHE II) score, low red blood cell count and high C-reactive protein levels were the risk factors highly associated with subsyndromal delirium symptoms. Older age, acute admission, steroid use, the utilisation of restraints and lower PaO2 were the determinants of progression to delirium.

CONCLUSIONS: A high incidence of sub syndromal delirium was observed in critically ill patients. Patient with sub syndromal delirium must be promptly identified and treated due to the risk of progression to delirium.