Factors causing acute delirium in critically ill adult patients: a systematic review

Delirium, also known as acute confusional state, is a clinical syndrome that is typified by a disturbance of consciousness, attention, cognition and perception. It is estimated that the incidence of delirium varies between 28.3% to 80% in intensive care patients. Delirium is most likely to affect older patients above the age of 65 years.

The primary focus of this systematic review was to synthesise the best available evidence to identify the factors which are associated with acute delirium in critically ill adult patients.

A three-step search strategy was utilised in this review. An initial limited search of MEDLINE and CINAHL was undertaken. A search strategy was then developed using identified keywords and MeSH headings. Lastly, the reference lists of all identified studies were examined. All searches were limited to English language studies published between 1990 and 2010.

The participants of this review were adult patients in a critical care setting who present with acute delirium in the intensive care unit.The review considered studies which examine the factors causing delirium in critically ill adult patients, such as fever, hypoxia and sepsis.This review considered studies that included the incidence of acute delirium as related to the individual factors as an outcome measure.This review considered any high quality quantitative papers that addressed factors causing acute delirium in intensive care unit patients. This review included data from cohort and case control studies.

The Joanna Briggs Institute Critical Appraisal Checklist for Cohort / Case Control Studies was used to assess methodological quality.

Data were extracted using a standardised Data Extraction Tool from the Joanna Briggs Institute. Due to the heterogeneous nature of the study methods, the findings of this systematic review are presented in a narrative summary.

Twenty-four papers were included in this review. Some factors were common; however certain factors were exclusive to the type of setting. With regards to pharmacological factors, benzodiazepines were the most likely medications to be associated with delirium as compared to other drugs used in the intensive care unit. With regards to biomarkers, a variety were implicated in causing delirium, such as apolipoprotein 4 genotype, plasma tryptophan, interleukin-6, cortisol and C-reactive protein. Older age was also found to be a common risk factor.

With regards to the medical and surgical intensive care units, relatively similar risk factors of older age and co-morbidity are significant. In the cardiac intensive care unit, a variety of risk factors were significant. Benzodiazepines have been singled out as the most likely drug to cause delirium. The biomarkers cortisol and hypoalbuminemia were also shown to be significant risk factors of delirium.

Future research should use increased sample sizes, recruited from more than one hospital, assessing diverse factors. Future studies could examine the effects of specific biomarkers on delirium.

By creating a regression model for delirium prediction, clinicians may be able to create a checklist to identify patients at risk of developing delirium. This checklist could assist in monitoring patients at higher risk for developing delirium, allowing measures to be implemented for preventing the incidence or reducing the severity of delirium. The use of benzodiazepines should also be avoided if possible, as they are seen to have a significant association with the incidence of delirium.