English

Abstract

Introduction Despite advances in understanding delirium over the past 30 years, adverse outcomes persist. We aim to review the literature pertaining to adverse outcomes, and their causes, associated with delirium in medical inpatients. Hypothesis Despite extensive research in delirium to date, delirium patients continue to suffer adverse outcomes. We offer four hypotheses as to why poor outcomes continue to be associated with delirium and propose new areas of research. Evaluation of hypothesis Delirium has been associated with institutionalization, increased length of hospital stay, cognitive and functional decline and mortality. Less is known, or even conjectured, in relation to the cause(s) of poor outcomes. Conclusion In the evidence gap, we have proposed a number of hypotheses that explore the attrition observed in delirium. These can be understood within the dynamic tension between frailty, emergent illness, triggers, unmet need and survival properties for patients at the limits of redundancy. Further research into the drivers behind poor outcomes is needed. Introduction Delirium is defined as an acute disruption of cognition and function in the context of a physiological insult and has been associated with 14%–56% of hospitalized older patients1–5. The importance of studying delirium in medical inpatients has largely been recognized over the past 30 years. Failure to properly diagnose and treat delirium appropriately results in significant morbidity and mortality with attendant healthcare costs6. The incidence of delirium during hospitalization has even been recognized as a sign of the quality of hospital care7. This paper will review the literature from 1981, representing the first published diagnostic criteria in delirium8, until the present. Adverse outcomes, and their causes, associated with medical inpatients diagnosed with delirium have been examined. Three recent systemic reviews were utilized to determine if any studies reporting on morbidity and mortality associated with delirium also reported on causes of adverse outcomes6,9,10. While delirium or acute confusional state has been described since Hippocrates10, it was not until the early 1980s that the American Psychiatric Association set forth criteria for diagnosing delirium as a unique psychiatric disorder in the Diagnostic and Statistical Manual of Mental Disorders version three (DSM-III)8. Studies conducted since that time have largely reported whether delirium among hospital inpatients was associated with increased length of hospital stay, death in hospital, and mortality, institutionalization, cognitive impairment, functional decline and increased need for care after discharge at varying periods (typically during hospitalization as well as at 1, 3, 6, 12 months and 2 years post-discharge)11–20. It should be pointed out that several of these studies recognized the limitations of the contemporary instruments and criteria utilized to assess cognitive function, as well as the need to differentiate the various subtypes of delirium to accurately describe the prevalence of outcomes12,14,19. Three subtypes of delirium have been described, hyperactive, hypoactive and mixed.9 Authors have noted that each subtype likely has its own aetiology and pathophysiology, but this awareness has not translated into operationalization of delirium phenomenology19,23. Furthermore, authors are using the DSM-IV diagnostic criteria for delirium and looking at adverse outcomes from delirium at extended lengths of time, up to 5 years3. Currently, the APA is reviewing the diagnostic criteria for delirium as the DSM-V is set to be released in May 201322. Most studies report an increase in mortality associated with delirium and additional adverse consequences extending to survivors (Table 1). Survival remains poor even after adjusting for multiple confounders including illness severity, disability and dementia.2 Delirium is no longer seen as transitory.11,13–15 In fact, Murray et al.13 reported that functional decline could be detected 3 months post-discharge and persist at 6 months. Loss of function alone accounted for reduced activities of daily living, dependency on caregivers, increased health-care needs, nursing home placements and associated costs.13 Delirium has been consistently shown to be associated with an increased risk of cognitive decline and dementia (as dementia is also a risk factor for delirium)14,15,20. No consensus was seen between the three subtypes with regard to mortality. However, some studies have reported that hypoactive delirium * Corresponding author Email: robert.renjel@uqconnect.edu.au; Eamonn_Eeles@health.qld.gov.au 1 University of Queensland, Brisbane, QLD, Australia 2 Department of Internal Medicine Services, The Prince Charles Hospital, Brisbane, QLD, Australia