Given the complex multifactorial causation and the probability that each individual episode of delirium has, a unique set of contributors, to isolate a single mechanism of delirium, is practically impossible. There is evidence amassing however highlighting how different sets of biological factors interacting can lead to acute cognitive dysfunction by interfering with large-scale neuronal networks. These include inflammation, metabolic imbalance, neurotransmitter derangement, physiological stressors, electrolyte imbalance and genetic abnormalities (Watt et al. 2013). We know that although delirium can occur at any age, children and older people are particularly vulnerable (Inouye et al. 2014); children obviously have less developed neuronal networks, and in older people they are more likely to have age-related damage to these networks, and so this further points favourably to the hypotheses that neuronal networks play a key role in the pathophysiology of delirium.

The high prevalence and complex presentation of delirium means it is important that appropriate tools are used to aid in its diagnosis. Delirium is often unrecognised and easy to overlook (Inouye et al. 2014), and as mentioned above it is important not to class all confused or inappropriate behaviour as delirium, as much as it is important not to excuse delirious behaviour because the patient has an underlying cognitive impairment, psychiatric history or dementia. While some potential has been explored for the use of EEG of CT/MRI neuroimaging for the diagnosis of delirium, it shows low yield in unselected patients (Agency for Healthcare research and Quality 2013). There are a number of validated tools which can be applied to diagnose delirium. The NICE guidelines (2010) recommend using the DSM criteria as a basis for clinical assessment or alternatively using the Confusion Assessment Method (CAM) (Inouye et al. 1990). CAM is a 5-min questionnaire by which the present severity and fluctuation of nine delirium features are identified (Wong et al. 2010). The features tested are acute onset, inattention, disorganised thinking, altered level of consciousness, disorientation, memory impairment, perception disturbances, psychomotor agitation or retardation and altered sleep wake cycle. Based on the DSM criteria for delirium, the questionnaire is in the form of the algorithm and is quick and easy to administer. The step-by-step process first establishes the essential features which are sudden onset and fluctuating course as well as inattention. The latter part features a test to establish either disorganised thinking or altered level of consciousness. So essentially if you have the first two features and either (or both) of the latter, you are diagnosed as CAM positive and delirious. CAM is by far the most widely used assessment tool for delirium (Inouye et al. 2014) and has been adapted for use in several specialist settings such as ICU and emergency departments. CAM has also been adapted for use in nursing home patients (Dosa et al. 2007). The NH-CAM rearranges the minimum data set items which were previously used to identify delirium in nursing homes into a similar structure as the original CAM (Fig. 14.1). Other tools used include the Clinical Assessment of Confusion (Vermeersch 1990), the Global Attentiveness Rating (O’keefe and Gosney 1997) and the Delirium Observation Screening Scale (Schuurmans et al. 2003); however given its simplicity, efficiency, adaptability and efficacy, the best evidence supports the use of CAM (Wong et al. 2010). As with any tool, the quality of outcome is dependent on the ability of the user, and so it is important that adequate training is engaged to use such tools. Another important factor, especially in those with pre-existing cognitive impairment or dementia, is establishing their baseline cognitive ability. Families and carers can play a vital role in the diagnosis of delirium, and in fact the CAM has further been adapted to allow for families and carers to assess for signs of delirium CAM-ICU (Steis et al. 2012).

Independently both dementia and delirium have a large impact effecting length of stay in hospital, healthcare costs, morbidity, mortality and loss of functional independence. These effects are amplified when DSD is considered; however, unfortunately the consequences of DSD remain a relatively neglected research area (Fick et al. 2005). While there is conflicting evidence in the data around DSD and mortality, there are strong suggestions that it can significantly add to risk of death (Bellelli et al. 2007). It has however been well established that delirium, as a stand-alone factor, has a significant impact on mortality (McCusker et al. 2002). DSD also has been found to have a significant impact on rehabilitation, mobility and functional independence. Morandi et al. (2014) have signified that DSD needs to be recognised by clinicians as a prognostic factor in rehab, reporting a significant negative effect on functional outcomes, as well as leading to institutionalisation of patients. A further study by Morandi et al. (2015a) considered the psychological and emotional impact of DSD on patients. The study reported increased anxiety, depression and low mood amongst people who had experienced DSD. O’Malley et al. (2008) found that the experiences of patients who had delirium could be grouped into three main themes, incomprehension and feelings of discomfort, the need to keep distance and to protect oneself, and interventions which diminish suffering. Delirium and DSD can also have a profound effect on family, caregivers and healthcare staff; an important note to take from Morandi et al. (2015b) is that while there were elements of distress in both the informal caregivers and healthcare staff, it was substantially higher in the informal carers.

Determining and correcting the underlying cause of delirium is the primary intervention in managing DSD, but the symptoms of delirium must be managed until the delirium is resolved. In general, the management of DSD can be classified into the two categories of non-pharmacologic and pharmacologic interventions. Non-pharmacologic interventions are preferred as first-line approaches because the medications used to treat the symptoms of delirium may actually exacerbate or prolong its course.