Delirium is a state of acutely occurred and transient cerebral dysfunction. It is a common complication in elderly patients after surgery. A systematic review showed that an average of 36.8% (range 0 to 73.5%) of surgical patients developed postoperative delirium, and its occurrence increased with age. According to our previous studies, postoperative delirium developed in 51.0% of patients after cardiac surgery and in 44.5% of patients after non-cardiac surgery. The occurrence of delirium is associated with worse short-term outcomes, including increased postoperative complications, prolonged hospital stay, and increased in-hospital mortality; it is also associated with worse long-term outcomes, including declined cognitive function, decreased quality of life, and increased post-hospital mortality. Delirium is the result of multiple factors. Studies showed that postoperative pain is an important risk factor of delirium, whereas good postoperative analgesia reduces the incidence of delirium. For postoperative patients, sleep disturbances occurs frequently and increases the risk of delirium, whereas improving sleep quality reduces the incidence of delirium. Furthermore, the studies found that surgery related inflammatory response also plays an important role in the development of delirium.

Dexmedetomidine is a highly selective alpha-2 (α2) adrenoreceptor agonist that provides anxiolysis, sedation, hypnosis and analgesia. It exerts the sedative and hypnotic effects by activating the endogenous sleep pathways, and produces a condition similar to phase 2 non-rapid eye movement sleep. For patients undergoing mechanical ventilation in the ICU, dexmedetomidine sedation helps to maintain a normal circadian rhythm of sleep and improves sleep architecture. Dexmedetomidine also provides analgesic effect by activating α2 adrenergic receptors in the dorsal horn of spinal cord. When used as a supplemental drug it decreases intraoperative and postoperative requirement of opioids. Moreover, animal studies showed that dexmedetomidine significantly inhibits the degree of inflammatory response induced by endotoxin or during spinal cord injury. In clinical studies, dexmedetomidine attenuates the degree of inflammatory response following Coronary Artery Bypass Grafting surgery.

These effects of dexmedetomidine make it suitable for prevention of postoperative delirium in high-risk patients. Studies have shown that, for ICU patients requiring mechanical ventilation, sedation with dexmedetomidine reduces the incidence of delirium when compared with other sedatives; for postoperative patients, dexmedetomidine administered in combined with opioids improves analgesia and reduces opioid requirements. A recent study showed that, for elderly patients admitted to the ICU after surgery, low-dose dexmedetomidine infusion (at a rate of 0.1 ug/kg/h, for an average of 15 hours) improves analgesia for up to 24 hours, ameliorates subjective sleep quality for up to 3 days, and reduces the incidence of delirium during the first 7 postoperative days. The investigators hypothesized that the use of dexmedetomidine as a supplement to patient-controlled intravenous analgesia may also reduce the incidence of postoperative delirium.