**3.1 Predisposing factors**

The predisposing factors are those that place patients vulnerable to develop delirium. Older age, neurological disorders, male sex, sensory impairment, , depression, functional dependence, immobility, hip fracture, dehydration, alcoholism, severity of physical illness, stroke, metabolic abnormalities are among the predisposing factors that increase an individual's vulnerability to delirium (Inouye, 1999; Burns et al., 2004; Fong et al., 2009; Staus, 2011). The National Clinical Guideline Center (in the UK) has published a data synthesis on this topic commissioned by the National Institute for Health and Clinical Excellence (NICE). In this analysis, the risk factors for delirium were reported as age 65 years or older, cognitive impairment (past or present) and/or dementia, hip fracture on admission, severe illness (a clinical condition that is deteriorating or is at risk of deterioration) (National Clinical Guideline Center).

### **3.1.1 Age**

One of the most important predisposing factors is age (Inouye, 1999). Both the geriatric and pediatric populations are at risk of developing delirium (Dulcan, 2010). The elderly are

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 &

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 is divided into subtypes according to the etiological factors. When there is evidence from the history, physical examination, or laboratory findings that the disturbance is caused by the direct physiological consequences of a general medical condition, it is called as *Delirium due to a general medical condition.* When the symptoms of delirium are due to substance intoxication, it is called as *Substance intoxication delirium*. When the delirium is due to substance withdrawal, it is called as *Substance withdrawal delirium.* When there is evidence from the history, physical examination, or laboratory findings that the delirium has more than one etiology, it is called as *Delirium due to multiple etiologies.* Delirium that is of unclear etiology is called as *Delirium not otherwise specified* (American Psychiatric Association, 2000). Delirium usually has a multifactorial etiology. It has been reported that 90% of patients with delirium had three to four identifiable etiologic factors, 27% had two factors, and only 16% had one identifiable etiologic factor (Camus et al., 2000). The etiology of delirium is complex and multifactorial, with the interaction of precipitating factors (acute insults) on a

The predisposing factors are those that place patients vulnerable to develop delirium. Older age, neurological disorders, male sex, sensory impairment, , depression, functional dependence, immobility, hip fracture, dehydration, alcoholism, severity of physical illness, stroke, metabolic abnormalities are among the predisposing factors that increase an individual's vulnerability to delirium (Inouye, 1999; Burns et al., 2004; Fong et al., 2009; Staus, 2011). The National Clinical Guideline Center (in the UK) has published a data synthesis on this topic commissioned by the National Institute for Health and Clinical Excellence (NICE). In this analysis, the risk factors for delirium were reported as age 65 years or older, cognitive impairment (past or present) and/or dementia, hip fracture on admission, severe illness (a clinical condition that is deteriorating or is at risk of

One of the most important predisposing factors is age (Inouye, 1999). Both the geriatric and pediatric populations are at risk of developing delirium (Dulcan, 2010). The elderly are

vulnerable patient with predisposing conditions (Inouye, 1999).

deterioration) (National Clinical Guideline Center).

Lawley, 2009, Fong et al., 2009).

delirium (Saxena & Lawley, 2009).

**3.1 Predisposing factors** 

**3.1.1 Age** 

**3. Etiology** 

more vulnerable to delirium because of the age-related loss of cholinergic reserve that is necessary for memory, learning, attention, and wakefulness (Maclullich et al., 2008).

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

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