IntroductionDespite 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 hypothesisDelirium 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. ConclusionIn 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.

Delirium has been associated with institutionalization, increased length of hospital stay, cognitive and functional decline and mortality. Research in the last thirty years has recognized that accurate diagnostic criteria allow for targeted interventions for those suffering from delirium. However, despite the advances made in understanding delirium, adverse outcomes persist. This article will first review how the evolution of diagnostic criteria has fostered improvements in the recognition of delirium and facilitated the development of therapeutic strategies. Second, we discuss how this foundation in approach to delirium has influenced outcomes and the evidence for causality. Finally, the candidate factors responsible for propagating adverse events are considered and future research direction outlined.