**3.2. Precipitating factors**

Precipitating factors are the acute insults that trigger the mechanisms resulting in delirium (Fong et al., 2009; Inouye, 1999). Factors that have been reported to precipitate delirium are: anemia (Joosten et al., 2006), hypoxaemia (Kazmierski et al., 2010), Intensive Care Unit admission (Branco et al., 2011), electrolyte abnormalities (Korevaar et al., 2005), sleep deprivation (Weinhouse et al., 2009), pain, bladder catheter use, drugs and surgery (Burns et al., 2004). Biochemical abnormalities such as hyponatremia and hypokalemia and hyperuricemia and low body mass index and sensory impairment reflects the severity of the underlying precipitating cause of delirium (Elie et al., 1998; Mussi et al., 1999).

Inouye and Charpentier performed a study to establish a predictive model for development of delirium and identified 5 independent precipitating factors for delirium in the elderly: use of physical restraints, malnutrition, more than 3 medications added, use of bladder catheter and any iatrogenic event (Inouye & Charpentier, 1996). Among the predisposing factors, surgery and drugs will be discussed in this section.
