**3.2.1 Surgery**

The incidence of post-operative delirium ranges from 5% to 15%(Deiner& Silverstein, 2009). Certain high-risk groups have increased rates of delirium. Delirium has been reported in 16.3% after cardiac surgery (Kazmierski et al., 2010). Rates as high as 30.2% after hip surgery (Lee et al., 2011) and 50% have been reported in elderly patients (Inouye et al., 1993; Dasgupta & Dumbrell, 2006). Factors that increase the risk of delirium in surgical patients include electrolyte disturbances, increased age, dementia, low cardiac output, perioperative hypotension, postoperative hypoxia, and use of anticholinergic drugs. (Michaud et al., 2007; Norkiene et al., 2007). Pandharipande et al. found that 70% of the combined surgical and trauma ICU patients had at least one episode of delirium (Pandharipande et al., 2007).
