MInimizing Delirium With Nasal Dexmedetomidine-InducEd Sleep (MIDDIES)

Inclusion Criteria: * Aged 65-90 years * Scheduled for a major abdominal surgery with estimated surgery time ≥ 2 hours Exclusion Criteria: * Blind, deafness or the inability to speak mandarin * Allergy to dexmedetomidine. * Renal and liver failure requiring dialysis or Child-Pugh score \> 5 * Follow-up difficulties (i.e. active substance abuse, psychotic disorder, homelessness) * Previous major abdominal or cardiac surgery within 1 year of surgical procedure * Chronic therapy with benzodiazepines and/or antipsychotics. Severe deficit due to structural or anoxic brain damage * Body weight \< 35 kg