Postoperative delirium (POD) is common in elderly patients after surgery and anesthesia which occurs within 24 to 72 hours after surgery. POD has adverse effects on early and long-term prognosis, including increased risk of postoperative complications, perioperative mortality, prolonged hospital stay, and increased incidence of long-term cognitive impairment and long-term mortality. The underlying mechanisms of POD are not fully understood, various hypotheses exist including neuroinflammation, neurotransmitter interference, and disturbances in communication throughout the brain network. The incidence of POD varies greatly among patients with different surgeries. POD can be as high as 50% in patients over 60 years of age after cardiac surgery, 8% to 54% after gastrointestinal surgery, and 5% to 14% after joint replacement surgery. In general, the incidence of POD in minor surgery is low, and the incidence of POD in major surgery is higher. The incidence of POD is significantly increased in patients over 65 years of age, and increases with age. POD also increases in patients with preoperative cognitive changes or coexisting diseases. With an increasing number of elderly patients undergoing surgery and anesthesia, POD has become a major global health challenge requiring urgent attention.

The bispectral index (BIS) is an electroencephalographic measurement commonly used to monitor the depth of anesthesia. BIS monitoring allows anesthesiologists to adjust medications according to the situation, allowing patients to recover from anesthesia more quickly and reduce the incidence of intraoperative awareness. Recent studies have shown that low intraoperative BIS value (BIS\<40) and prolonged duration of low BIS value are both risk factors of POD which can predict the occurrence of POD. Low cerebral oxygen saturation is also risk factor of POD. The stability of BIS during general anesthesia may affect the risk of POD in elderly patients. Therefore, it is very important to maintain a stable BIS value as much as possible during general anesthesia surgery, and a general anesthetic with good BIS stability is even more needed in clinical practice.

Propofol is the most commonly used general anesthesia sedative during general anesthesia surgery. However, adverse events such as BIS burst suppression during induction and maintenance of general anesthesia are frequently associated with propofol. BIS stability is closely related to the incidence, prognosis and functional recovery of POD in elderly patients. Cyclopofol (a new type of anesthetic/sedative) has been approved by the Chinese Food and Drug Administration for "sedation and anesthesia during non-tracheal intubation surgery/operation", "general anesthesia induction and maintenance" and "intensive care during intensive care". "Sedation and anesthesia for outpatient surgery in gynecology" is still under consideration. Cyclopofol provides general anesthesia/sedation with good efficacy and safety.

Cyclopofol has the effect of stabilizing BIS. According to the results of the Phase III clinical study on induction and maintenance of general anesthesia with cyclopofol (study number HSK3486-302), the average range of BIS in the cyclopofol group was significantly smaller than that in the propofol group, and the lowest or highest BIS value between 30 and 60 was higher than that in the propofol group, and the highest BIS value \>60 was significantly lower than that in the propofol group, indicating that the change of BIS after cyclopofol administration was more stable than that of propofol group. Consequently, cyclopofol may reduce POD, improve prognosis, and provide brain protection.