The incidence of postoperative delirium with dexmedetomidine was found to be lower than that of a placebo, propofol, sevoflurane, and midazolam, regardless of whether the extubation time was longer than 1 or 5 h, the operation time was less than 3 h or more than 3 h, or whether the surgery was cardiac or non-cardiac. This indicates that dexmedetomidine has a positive effect on preventing postoperative delirium. However, it should be noted that dexmedetomidine carries a higher risk of reducing heart rate than normal saline. Therefore, it is necessary to closely monitor heart rate when using dexmedetomidine and discontinue the drug promptly if necessary.

Our analysis supports previous research and guidelines [27], indicating that dexmedetomidine can play a positive role in preventing postoperative delirium [28, 29]. A large randomized study showed that dexmedetomidine does not reduce the incidence of postoperative delirium. It is possible that other side effects, such as hypotension, could contribute to the occurrence of postoperative delirium. Therefore, the conclusion can be drawn that there is no significant difference in the rate of postoperative delirium between the dexmedetomidine group and the normal group. Furthermore, it is important to acknowledge that postoperative delirium can be caused by multiple factors, which necessitates a comprehensive and dialectic evaluation. dexmedetomidine functions by inhibiting the release of norepinephrine through the activation of α2 receptors in the brain, which reduces the excitability of neurons and enhances the inhibitory effect of γ-aminobutyric acid (GABA). This mechanism can provide analgesic effects, relax patients, and reduce anxiety [30]. Dexmedetomidine can also improve postoperative sedation and sleep quality, and reduce sensory perception, nerve exhaustion, and stress response, promoting better patient recovery [31]. Finally, dexmedetomidine may have a positive effect on the prevention of postoperative delirium by regulating the inflammatory response and metabolic activity of neurons in the brain, thus exerting anti-inflammatory and neuroprotective effects [20, 32]. Therefore, the use of dexmedetomidine is effective in preventing postoperative delirium.

Our analysis found that compared to saline, midazolam, sevoflurane, and propofol, dexmedetomidine is more likely to cause bradycardia, but there was no significant difference in the incidence of hypotension among all sedatives. We identified 12 articles reporting bradycardia and 12 articles reporting hypotension among the total of 41 articles included in our analysis. However, due to the limited number of articles available on hypotension and bradycardia, we do not have sufficient evidence to establish the differences between different sedatives. Clinicians should consider the potential side effects when administering drugs to patients.

According to some guidelines, the duration of surgical procedures is recognized as one of the factors that affect the occurrence of postoperative delirium. However, different studies appear to have arrived at varying conclusions regarding the specific length of time required to increase the risk of developing this condition [33]. Some studies have suggested that the rate of postoperative delirium increases significantly if the surgical procedure takes more than 2 h [34], while others suggest that the threshold could be 3, 4, or even 5 h [35,36,37]. In our study, we observed that when the duration of surgery exceeded three hours, administering dexmedetomidine had a significantly greater effect in preventing postoperative delirium compared to the other anesthesia regimen. The incidence of postoperative delirium was significantly reduced in surgeries lasting less than three hours, where patients were administered dexmedetomidine compared to the usage of normal saline as part of the anesthesia regimen. The specific duration and threshold for postoperative delirium risk may depend on factors such as the type and location of surgery, the patient’s health status, and anesthesia-related factors. Therefore, clinicians need to consider various risk factors carefully for each patient and surgical procedure to minimize the risk of postoperative delirium.

Extubation is the process of removing a breathing tube that is inserted into a patient’s airway during surgery to help them breathe. The longer the duration of extubation (the amount of time the breathing tube is in place), the higher the risk of postoperative delirium [38, 39]. This is because the tube can cause irritation and inflammation in the airways, which can trigger an inflammatory response in the body that can lead to cognitive issues [40, 41]. A study looked at the relationship between extubation duration and postoperative delirium in elderly patients undergoing cardiopulmonary bypass. The study found that patients who had a longer duration of extubation were more likely to develop postoperative delirium, compared to patients who had a shorter duration of extubation. Our study found that the extubation time for patients who received propofol and sevoflurane was longer compared to those who received dexmedetomidine, midazolam, and normal saline. Previous studies have demonstrated that the use of dexmedetomidine in intubated patients has a sedative effect, reducing restlessness and preventing postoperative delirium [42,43,44,45]. Our study further supports this finding, as we observed a positive effect of dexmedetomidine in preventing postoperative delirium regardless of the length of intubation.

Numerous studies have demonstrated that the use of dexmedetomidine can decrease the incidence of postoperative delirium [16, 46,47,48], although a few have reported otherwise [49, 50]. Postoperative delirium is associated with various factors such as the type of operation, age, the patient’s overall health status, excessive blood loss, and abnormal liver and kidney function. While dexmedetomidine has primarily been studied in the context of cardiac surgery, some research has shown that it can also be effective in preventing postoperative delirium in non-cardiac surgical procedures [51,52,53,54]. Our study provides further evidence in support of dexmedetomidine’s effectiveness, finding that it can reduce the incidence of postoperative delirium not only after cardiac surgery but also after non-cardiac surgical procedures.

This study has several strengths. First, this meta-analysis updates results from clinical studies over the past two years, thus several recently published, large-scale, and high-quality RCTs have been included. Second, to increase the credibility of the study, our study excluded clinical experiments with the number of participants in each group being less than 20. Finally, we also increased the effect of intubation time and operation time on postoperative delirium.

Our net-meta analysis has some limitations that need to be addressed. Firstly, some studies have smaller sample sizes, with only 40 subjects, which could affect the generalizability of the findings. Secondly, we only compared four sedatives, while there are likely more than four drugs used in clinical settings. Thirdly, postoperative delirium is multi-factorial and can be influenced by several variables such as age, type of operation, operation time, and intraoperative medication. Our analysis did not consider these factors. Lastly, the scale of postoperative delirium is subjective, which could influence the accuracy of the results.