Postoperative delirium in older people may be contributed to by intrinsic brain vulnerability such as pre-existing dementia. Some cognitively intact older people also experience postoperative delirium and in these patients some go on to develop later dementia. The investigators propose that postoperative delirium may be an unmasking of covert brain vulnerability by the dyshomeostasis of the anaesthesia/surgical intervention.~In people with dementia or mild cognitive impairment, electroencephalography (EEG) studies have shown slowing of brain wave activity, especially in the back of the brain.~Processed electroencephalography, using a limited number of channels, is routinely used during anaesthesia to aid assessment of anaesthetic depth of the patient.~In this study the investigators will assess the feasibility of acquiring EEG data from the front and back of the brain. The investigators will also explore the data for early signals of brain vulnerability
An assessment of difference in prespecified processed electroencephalography variables between cognitively intact older surgical patients who develop postoperative delirium compared to those who do not develop postoperative delirium