**2.1 Prevalence**

The prevalence of delirium varies with the population that is being studied (Fong et al., 2009). Delirium is a relatively common disorder, especially in older people with physical illness (Saxena & Lawley, 2009). Community rates of delirium are reported to vary from 0.4% to 2% (Saxena & Lawley, 2009, Fong et al., 2009). In general hospital setting prevalence of delirium has been reported to range from 11% to 33% on admission (Lindesay et al., 2002) and its incidence during hospital stay ranges between 3% and 56% (Inouye, 2006; Michaud L et al., 2007).

A Review of the Etiology Delirium 191

more vulnerable to delirium because of the age-related loss of cholinergic reserve that is

Among this age group, one of the most common risk factors for delirium is dementia, with two-thirds of elderly cases of delirium having comorbid dementia (Fong et al., 2009). Delirium and dementia are both associated with cholinergic deficiency (Hshieh et al., 2008) and decreased cerebral blood flow or metabolism (Fong et al., 2006, Yokota et al., 2003); these common properties might explain the relationship between these two conditions

As mentioned above, the main mechanism that predisposes elderly to delirium is diminished cholinergic reserve; on the other extremes of age are children who are also prone to delirium because of the immature and evolving structural brain development (Williams, 2007). According to the study of Leentijens et al., 2008, etiological factors differed among pediatric, adult and geriatric populations; for children neurological, respiratory and circulatory disorders were among the most important causes of delirium (with ratios of 39%, %26, %17 in order), whereas for adults the most common factors were medication intoxication or withdrawal (24**%**), brain metastases/CNS neoplasms (24**%**) and metabolic and endocrine causes(20%), for elderly patients metabolic and endocrine causes (26%), systemic effects of a neoplasm (19%),medication intoxication or withdrawal (19%) were

Dementia is a major predisposing factor for delirium, a meta-analysis suggesting a relative risk of 5.2 (Elie et al., 1998). Fick et al. reported that approximately 45% of patients with dementia develop delirium during hospitalization (2002). Elderly patients with dementia are at higher risk for developing delirium not only because they have the usual age-related decrease in acetylcholine described previously, but also have a focal loss of acetylcholine due to death of the cholinergic cells in the nucleus basalis of Meynert as a result of the

In a study that included patients over the age of 65 years admitted to hospital with a fractured neck of femur, cognitive impairment which was measured by the Mini-Mental State Examination (MMSE), has been found to be the most significant predisposing factor

Other neurological causes are cerebrovascular diseases (thrombosis, embolism, arteritis, hemorrhage, hypertensive encephalopathy), degenerative disorders (multiple sclerosis), epilepsy, head trauma, space-occupying lesions (tumor, subdural hematoma, abscess,

Hip fracture patients are at increased risk of delirium because of the trauma associated with the injury and the rapid progression to hospitalization and surgery, in addition to the pain and loss of function (Schor et al., 1992; Williams et al., 1985). Delirium has been reported to be seen in 20%–40% of patients with hip fracture at the time of hospital admission

necessary for memory, learning, attention, and wakefulness (Maclullich et al., 2008).

(Eikelenboom and Hoogendijk, 1999; Fong et al., 2009).

most important factors (Leentijens et al., 2008).

**3.1.2 Neurological disorders** 

disease process (Tune & Egeli, 1999).

**3.1.3 Hip fracture** 

for the development of delirium (Freter et al., 2005).

aneurysm) and encephalitis (Michaud et al., 2007; Fong et al., 2009).

(Magaziner et al., 1989; Gustafson et al., 1991; Marcantonio et al., 2002 ).

Delirium rates depend on the setting in which the patient belong; for example, delirium prevalence has been reported to be between 7-10% in emergency department, whereas it has been reported to be as high as 33% in the orthopedic surgery patients (Samuels & Neugroschl, 2005). Postoperative delirium is reported to be in 15% to 62% of elderly patients (Saxena & Lawley, 2009, Fong et al., 2009). Higher rates of delirium have been reported in elderly patients in intensive care units (ICU), which ranges from 70% to 87% (Saxena & Lawley, 2009, Fong et al., 2009).

Children are also are at risk of delirium. There is a paucity of data on the rates of delirium in children, but delirium was reported to be seen in 10 to 40 percent of preschool children during emergence from anesthesia. Children with severe burns and fever are at risk for delirium (Saxena & Lawley, 2009).
