BackgroundDelirium is a common and serious problem among acutely unwell persons. Alhough linked to higher rates of mortality, institutionalisation and dementia, it remains underdiagnosed. Careful consideration of its phenomenology is warranted to improve detection and therefore mitigate some of its clinical impact. The publication of the fifth edition of the Diagnostic and Statistical Manual of the American Psychiatric Association (DSM-5) provides an opportunity to examine the constructs underlying delirium as a clinical entity.DiscussionAltered consciousness has been regarded as a core feature of delirium; the fact that consciousness itself should be physiologically disrupted due to acute illness attests to its clinical urgency. DSM-5 now operationalises ‘consciousness’ as ‘changes in attention’. It should be recognised that attention relates to content of consciousness, but arousal corresponds to level of consciousness. Reduced arousal is also associated with adverse outcomes. Attention and arousal are hierarchically related; level of arousal must be sufficient before attention can be reasonably tested.SummaryOur conceptualisation of delirium must extend beyond what can be assessed through cognitive testing (attention) and accept that altered arousal is fundamental. Understanding the DSM-5 criteria explicitly in this way offers the most inclusive and clinically safe interpretation.

Delirium is the most common neuropsychiatric complication seen in patients with cancer, and it is associated with significant morbidity and mortality. Increased health care costs, prolonged hospital stays, and long-term cognitive decline are other well-recognized adverse outcomes of delirium. Improved recognition of delirium and early treatment are important in diminishing such morbidity. There has been an increasing number of studies published in the literature over the last 10 years regarding delirium treatment as well as prevention. Antipsychotics, cholinesterase inhibitors, and alpha-2 agonists are the three groups of medications that have been studied in randomized controlled trials in different patient populations. In patients with cancer, the evidence is most clearly supportive of short-term, low-dose use of antipsychotics for controlling the symptoms of delirium, with close monitoring for possible adverse effects, especially in older patients with multiple medical comorbidities. Nonpharmacologic interventions also appear to have a beneficial role in the treatment of patients with cancer who have or are at risk for delirium. This article presents evidence-based recommendations based on the results of pharmacologic and nonpharmacologic studies of the treatment and prevention of delirium.