Children and the elderly reportedly are at higher risk to the development of delirium under circumstances of physiological stress 4,5,6. While the elderly are thought to be more vulnerable because of diminished cholinergic reserve, children are thought to be more vulnerable because of immature and evolving structural and biochemical brain development. Intrinsic predisposing patient vulnerabilities in addition to age would include a previous delirium episode, preexisting cognitive impairment, a CNS disorder, and increased blood–brain barrier permeability. Environmental risk factors include social isolation, sensory extremes, visual or hearing deficits, immobility, as well as environmental novelty or stress. Other risk factors include medical illness, surgery, and pharmacological influences. Clearly, during hospitalization, there is often a confluence of these predisposing and precipitating factors.

Some of the above risk factors may be modifiable and consequently present opportunities for preventive intervention. Closer observation of patients at high risk for delirium could allow for earlier detection of emergent delirium and allow for attenuation of modifiable risk factors. Probably most readily modifiable is medication exposure, particularly of anticholinergic medications (7). Because of the general acceptance of a tendency for children to regress under stressful circumstances, milder forms of delirium may be mistaken for simply regressive or provocative behavior. As with adults, however, undetected delirium may proceed to the point of self-injury or serious interference with medical treatment.

Paradoxically, children may have a reduced risk of postcardiotomy delirium compared to adults. Kornfeld et al (8). reported on a sample of 119 unselected open heart patients that included 20 children who had surgical procedures for repair of congenital lesions. Only one of the children developed delirium, whereas 30% of the adults operated on for congenital repairs did. It is noteworthy that preoperative psychiatric interviews may reduce postoperative delirium and psychosis by 50% (9). Others have also reported the benefit of using preoperative psychological interventions to reduce anxiety and improve perioperative management in children (10). A clinical consensus suggests that as the severity of pathophysiologic strain increases, so does the probability of developing a delirium (11). This is particularly true for burn patients, as well as for postoperative patients. Additional factors that are considered to foster the development of delirium include sleep deprivation, sensory deprivation, and sensory overload. Thiamine deficiency can be a risk factor for delirium in pediatric intensive care and oncology patients (12). Low serum albumin is another factor, resulting in a greater bioavailability of drugs that are transmitted in the bloodstream, potentially contributing to delirium (13).

Given that there is a wide variety of etiologies for delirium, it may be most useful to conceptualize delirium as a final common neural pathway that leads to its characteristic symptoms (4). These symptoms often fluctuate in intensity over a 24-hour period and may be associated with shifts between hypoactive and hyperactive states or with disruption of the sleep-wake cycle. Table 5.11.2 outlines symptoms generally associated with delirium that may be variably represented in different patients. Review of studies of delirium in adults with a variety of underlying etiologies shows that some symptoms are reported more often and more consistently than others, suggesting that there may be some core symptoms, irrespective of etiology. Postulated core symptoms include attentional deficits, memory impairment, disorientation, sleep-wake cycle disturbance, thought process abnormalities, motoric alterations, and language disturbances. Associated or noncore symptoms would include perceptual disturbances, (illusions, hallucinations), delusions, and affective changes (14). The associated symptoms might reflect the impact of either specific etiological influences or individual differences in brain circuitry and vulnerability.

Some studies suggest that the motoric profile in delirium is influenced by etiology. Thus, delirium due to drug and alcohol related causes is more commonly hyperactive, whereas delirium due to metabolic disturbances, including hypoxia, is more frequently hypoactive 15,16. As yet, however, available studies have not provided clear evidence that gross motoric subtypes have discernible neurobiological mechanisms.

Mortality rates during a hospitalization involving delirium for adults have ranged from 1.5% to 65% in different case series (17). Turkel and Tavare (18) retrospectively reviewed 84 children and adolescents with delirium, among 1,027 consecutive inpatient psychiatric consultations during a 4-year period. They found a mortality rate of 20% and a prolonged length of stay when delirium was documented. It is clear therefore that the diagnosis of delirium constitutes a matter of severe medical urgency. Since some of the medical conditions contributing to delirium are potentially reversible, early clarification of diagnosis and aggressive initiation of treatment are clinically imperative.

When a diagnosis of delirium is established, a thorough search for causes must be pursued, insofar as correction or amelioration of specific underlying causes is important in reversing the condition. However, this process of investigation should not unduly delay prompt treatment of the delirium itself, since such treatment can reduce symptoms even before
the underlying medical causes have been reversed. As noted above, from a DSM-IV-TR perspective, delirium is broadly categorized according to etiology into five groups. These include delirium due to a general medical condition, due to substance use or withdrawal, due to multiple causes, and due to no apparent cause that can be identified. It is probably useful to spell out in more detail a list of the wide variety of etiologies that may pertain, either individually or in combination. These are listed in Table 5.11.3.

Delirium in children and adolescents involves the same categories of etiologies as adults, though the relative frequency of specific etiologies differs. Thus, delirium related to illicit drugs is more common in the child and adolescent age group, as is the incidence of delirium from hypoxia due to foreign body inhalation, drowning and asthma, as well as delirium related to head trauma.

Delirium frequently goes undetected in a variety of therapeutic settings by a variety of medical specialists, including neurologists and psychiatrists (19). Failure of detection may derive from insidious onset and fluctuating course involving multiple symptom constellations that can generate much clinical variability. Thus an agitated, hyperactive delirium, that is more likely to be recognized, contrasts with the more common, mixed or hypoactive symptom pattern that may be more readily overlooked. This is particularly true in a hospital setting, with multiple shift changes of staff, where subtle and gradual changes of mental status may not be discerned. Diagnosis can be improved by routinely assessing cognitive function, by improving staff awareness of the varied presentations of delirium, and by using one of the screening instruments for delirium currently available (4).

Differential diagnosis includes depression, psychosis, anxiety, somatoform disorders, dementia (more commonly in the elderly) and, particularly in children, behavioral disturbance. Because of the general tendency for children to regress under stressful circumstances, milder forms of delirium may be mistaken for simply regressive or provocative behavior. As with adults, however, undetected delirium may proceed to the point of self-injury or serious interference with medical treatment. Effective diagnosis requires close attention to symptom pattern, temporal sequence, and objective clinical test results (laboratory, cognitive, electroencephalographic). Since delirium is often the first indication of serious medical deterioration, any patient manifesting an abrupt decline in attentional or cognitive function should be evaluated for possible delirium.

To allow more accurate diagnosis and monitoring, more than 10 different assessment instruments suitable for adults have been developed (20). One of these, the Delirium Rating Scale, has been systematically evaluated retrospectively with 84 children and adolescents diagnosed with delirium (age range 6 months to 19 years) (21). The Delirium Rating Scale is composed of 10 items: Two items ascertain the temporal onset of symptoms and their relationship to a physical disorder; eight other items evaluate major symptoms of delirium. These eight items rate perceptual disturbances, hallucinations, delusions, changes in psychomotor behavior, diffuse cognitive dysfunction, disturbances of sleep-wake cycle, lability of mood, and variability of symptoms. The cognitive dysfunction item includes impairment of attention, concentration, and memory. The results of the Turkel et al. study (21) suggest that the Delirium Rating Scale can be used effectively to evaluate delirium in the pediatric population.