Objective: Although numerous risk factors for delirium in the ICU have been proposed, the strength of evidence supporting each risk factor remains unclear. This study systematically identifies risk factors for delirium in critically ill adults where current evidence is strongest.
Data sources: CINAHL, EMBASE, MEDLINE, the Cochrane Central Register for Controlled Trials, and the Cochrane Database of Systematic Reviews.
Study selection: Studies published from 2000 to February 2013 that evaluated critically ill adults, not undergoing cardiac surgery, for delirium, and used either multivariable analysis or randomization to evaluate variables as potential risk factors for delirium.
Data extraction: Data were abstracted in duplicate, and quality was scored using Scottish Intercollegiate Guidelines Network checklists (i.e., high, acceptable, and low). Using a best-evidence synthesis each variable was evaluated using 3 criteria: the number of studies investigating it, the quality of these studies, and whether the direction of association was consistent across the studies. Strengths of association were not summarized. Strength of evidence was defined as strong (consistent findings in ≥2 high quality studies), moderate (consistent findings in 1 high quality study and ≥1 acceptable quality studies), inconclusive (inconsistent findings or 1 high quality study or consistent findings in only acceptable quality/low quality studies) or no evidence available.
Data synthesis: Among 33 studies included, 70% were high quality. There was strong evidence that age, dementia, hypertension, pre-ICU emergency surgery or trauma, Acute Physiology and Chronic Health Evaluation II score, mechanical ventilation, metabolic acidosis, delirium on the prior day, and coma are risk factors for delirium, that gender is not associated with delirium, and that use of dexmedetomidine is associated with a lower delirium prevalence. There is moderate evidence that multiple organ failure is a risk factor for delirium.
Conclusions: Only 11 putative risk factors for delirium are supported by either strong or moderate level of evidence. These factors should be considered when designing delirium prevention strategies or controlling for confounding in future etiologic studies.