Disturbance of consciousness refers to impairments in attention and the ability to be aware of and sustain attention to the environment (APA, 1999b). Attention is typically fluctuating and may present as a change in the level of consciousness that does not reach the level of stupor or coma. Patients may demonstrate slowed or inadequate reactions to stimuli or manifest distractibility. Individuals may be unable to follow conversations or complete simple tasks, may have slow response time, may be unable to maintain eye contact, or may fall asleep between stimuli. Increasing stimuli (touch, sound) may be needed to elicit a response. Conversely, patients may be hyperalert and overattentive to cues or objects in the environment. The ability to focus can be assessed by the patient’s ability to complete a particular task such as spelling the word “world” backward, subtracting serial 7s, or listing the days of the week in reverse order (Tune, 2000).

Many aspects of cognitive function are impaired in delirium, including orientation, memory, language, thinking, and perception (APA, 1999b; Tune, 2000). Disorientation usually manifests relevant to time or place, with time disorientation being the first to be affected. Disorientation to other persons occurs commonly, but disorientation to self is very rare. Short-term memory deficits are the most evident memory impairments. Immediate memory (over a period of seconds) is demonstrated by the digit span (a healthy older adult should be able to repeat at least five) while anterograde memory (over a period of minutes) is demonstrated by the ability to remember three objects after 5 to 10 minutes (Burns et al., 2005; Goy & Ganzini, 2003). However, because these tests also reflect attention, severe deficits in this area will affect results. Language disturbances include a lack of fluency and spontaneity (long pauses and use of repetitious phrases), a tendency to ramble and switch from topic to topic, and difficulty finding the correct word to use in conversation or naming objects (anomia). Thinking is usually disorganized as evidenced by incoherent speech, deficits in logic, and responses that are irrelevant to questions asked. Perceptual disturbances may include misinterpretations, illusions, or hallucinations. Visual misperceptions and hallucinations are most common, but auditory, tactile, gustatory, and olfactory misperceptions or hallucinations can also occur. The individual with delirium may have the delusional conviction that the hallucination is real and exhibit emotional and behavioral responses consistent with the hallucination’s content.

The features of confusion that develops over a short period and fluctuates over the course of the day are important defining criteria for delirium. Symptoms develop over hours or days but are likely to be intermittent in presentation and severity. A typical presentation is worsening of symptoms at night with lucid periods during the day where the patient may function normally (Cole, 2004). Noting the onset of the disturbances in consciousness or cognition assists in differentiating delirium from other syndromes that cause mental status changes, such as dementia.

An important criterion for the diagnosis of delirium is evidence that the changes are a physiological consequence of an underlying medical condition, substance or medication intoxication or withdrawal, or combination of these factors. In palliative and end-of-life care, it may be difficult to identify the exact cause of delirium. An individual may have several potential causes at any one time (see “Etiology and Pathophysiology”). The challenge for the clinician is to identify which of the potential causes is the most likely and then determine the appropriate approach to this problem.

Disturbances in sleep patterns include daytime sleepiness, nocturnal insomnia, disturbed sleep continuity, and excessive dreaming. Some patients may experience a complete reversal of the sleep-wake cycle characterized by diurnal sleep periods and nighttime agitation and insomnia, whereas others may have fragmentation of the circadian sleep-wake cycle characterized by short periods of sleep and waking across the 24-hour day (Burns et al., 2005; Trzepacz, Mittal, Torres et al., 2001).

Patients with delirium may also exhibit disturbed psychomotor activity. Continuing research has indicated that there are several subtypes of delirium based on motor activity. These include a hyperactive-hyperalert subtype, a hypoactive-hypoalert subtype, and a mixed subtype that features components of the other two (Camus, Burtin, Simeone et al., 2000; Meagher & Trzepacz, 2000; Ross, Peyser, Shapiro et al., 1991). Patients with hyperactive-hyperalert delirium show evidence of sympathetic nervous system overactivity manifested in restlessness or agitation. This subtype is the most commonly recognized probably due to the expected presentation of agitation and/or inappropriate behavior (Inouye, Foreman, Mion et al., 2001). Characteristics of hyperactive-hyperalert delirium include plucking at bedclothes, wandering, verbal or physical aggression, increased alertness to stimuli, psychosis, and mood lability. Hypoactive-hypoalert patients appear lethargic and drowsy, respond slowly to questions, and do not initiate movement. This type of delirium is characterized by withdrawal from people and usual activities and decreased responsiveness to stimuli. Because they are quiet and withdrawn, the delirium in these patients is often overlooked or attributed to dementia, depression, or senescence (Casarett, Inouye, & American College of Physicians, 2001; Inouye et al., 2001). Differentiating delirium from normal aging processes, dementia, or depression requires careful and repeated assessment. A patient with a mixed subtype shows alternating periods of both types of behavior. Periods of lethargy may be seen as clinical improvements, when in fact the delirium may be continuing and increasing in severity (Clary & Krishnan, 2001; Milisen, Foreman, Godderis et al., 1998). A complete assessment of all symptoms of delirium is required before a change in behavior can be labeled as an improvement.

Patients with delirium may exhibit emotional disturbances. Anxiety, fear, depression, irritability, anger, euphoria, and apathy are common, with anxiety being the prevailing emotion. The delirious patient may be emotionally labile, rapidly and unpredictably shifting from one emotional state to another (APA, 1999b).

Some patients have prodromal symptoms such as restlessness, anxiety, irritability, distractibility, or sleep disturbance that progress to overt delirium over 1 to 3 days (APA, 1999b). Recently, Cole and colleagues described a condition known as subsyndromal delirium (SSD) (Cole, McCusker, Dendukuri et al., 2003). The symptoms of SSD are similar to prodromal symptoms, but the patient never progresses to overt delirium. Patients with SSD have the same risk factors and similar outcomes as those with delirium. These findings suggest that delirium is a spectrum disorder in which increasing numbers of symptoms are associated with increasingly adverse consequences. Patients noted to be exhibiting one or more prodromal symptoms or who report feeling “mixed up,” having difficulty judging the passing of time, and having difficulty thinking or concentrating should be assessed for potentially reversible causes of delirium, and appropriate interventions should be initiated.