Study selection
In the initial search, a total of 1,527 potential articles were identified. After the initial screening of abstracts and titles, 1,448 articles were excluded based on the inclusion and exclusion criteria. The remaining 78 articles were collected for full text review, after the secondary screening and carefully inspection of these articles, 21 studies including 2,902 patients published between 2012 and 2020 were eventually selected for final analysis. Another 57 articles were excluded; 14 studies reported animal trials or basic experiments, 13 studies demonstrated DEX combined with other sedative agents (benzodiazepines, midazolam, and propofol), 8 studies described POCD in patients with local or spinal anesthesia, the quality of 8 studies with Jadad score≤3 points were poor, 5 articles described POCD in adolescents, 5 studies did not provide complete data, 4 studies were reviews and meta-analyses. The detail processes of study screening and selection were shown in the flow diagram (Fig.1).
Study characteristics
All of the studies enrolled for our meta-analysis were RCTs. In total of 21 studies involved 2,902 patients administered DEX(1,350) and saline/comparator(1,552). All included studies published between 2012 and 2020. Among them, 19 studies were from China, one study was performed in The United States and Africa, respectively. With regard to the incidence of POCD in our meta-analysis, 14 studies with 1,639 patients demonstrated the relationship between DEX and the incidence of POCD on the first day after surgery. 9 articles with 1,328 patients illustrated the association between DEX and the incidence of POCD on the third day after surgery. 5 literatures with 968 patients shown the relation between DEX and the incidence of POCD on the seventh day after surgery. Concerning the relationship between DEX and MMSE score, 9 studies with 800 patients described the relationship between DEX and the MMSE score on the first day after surgery. 8 articles with 976 patients reported the association between DEX and the MMSE score on the third day after surgery. 4 researches with 628 patients reported the association between DEX and the MMSE score on the seventh day after surgery. Dosage of DEX was in the range of 0.5 to 1.5ug/kg followed by continuous infusion at a rate of 0.15 to 0.80ug/kg/h. The majority of included studies investigated the elderly. The basic characteristics of each of the enrolled studies, including publication year, country, average age, number of cases, surgical type, administrations for patients, incidence of POCD, MMSE and Jadad score, were shown in Table 1. Quality of the included studies was generally moderate to good.
The association between DEX and the incidence of POCD
14 studies including 1,639 patients reported the relationship between DEX and the incidence of POCD on the first day after surgery. There was an obvious heterogeneity between the studies (P=0.009, I2=52%, Fig. 2) , therefore, a random effect model was applied. Our results clearly showed that the incidence of POCD in DEX group was significantly lower than the control group (OR=0.36, 95% CI 0.24-0.54, Fig.2). Meta-analysis of these 14 studies depicted that the administration of intraoperative DEX could reduce the incidence of POCD on the first day after surgery compared to placebo.
9 studies including 1,328 patients elaborated the association between DEX and the incidence of POCD on the third postoperative day. Considering no obvious heterogeneity between the studies (I2=0%,P=0.49, Fig.3), a fixed-effects model was adopted. The results of our meta-analysis suggested that the incidence of POCD in DEX group was significantly lower than controls (OR=0.45,95% CI 0.33–0.61, Fig.3). Meta-analysis of these 9 studies indicated that the intraoperative DEX could obviously lower the incidence of POCD on the third day after surgery compared to control group.
5 literatures including 968 patients reported the incidence of POCD on the seventh day after surgery. On account of the little heterogeneity (I2=47%,P=0.11, Fig.4), we applied a fixed-effects model in this study. Our result clearly shown that the incidence of POCD in DEX group was obviously lower than the saline/comparator group on the seventh postoperative day (OR=0.40,95% CI 0.26–0.60,Fig.4). Meta-analysis of these 5 studies shown that the intraoperative DEX could reduce the incidence of POCD on the seventh day after surgery compared to saline.
The association between DEX and the postoperative MMSE score
9 studies with 800 participants reported the relationship between DEX and the postoperative MMSE score on the first day after surgery. As we all know, MMSE is commonly used to assess cognitive function, a higher MMSE score indicates better cognitive function for postoperative patients. There was an obvious heterogeneity between the studies (P<0.00001, I2=96%, Fig. 5) , therefore, a random effect model was applied. Our results clearly showed that the MMSE score in DEX group was higher than the control group (SMD=1.24, 95% CI 1.08-1.41, Fig.5). Meta-analysis of these 9 studies revealed that the intraoperative use of DEX could improve postoperative cognitive function on the first day after surgery compared to placebo.
8studies involving 976 patients reported the MMSE score on the third postoperative day. A random effect model was adopted for meta-analysis considering the apparent heterogeneity (P<0.00001, I2=98%,Fig.6). The results from meta-analysis suggested that MMSE score was higher on the third postoperative day in the DEX group than the control group (SMD= 1.09, 95%CI 0.94-1.24, Fig.6). Meta-analysis of these 8 studies clearly showed that the intraoperative use of DEX could improve postoperative cognitive function on the third postoperative day compared to saline.
4 articles including 628 patients reported the association between DEX and the MMSE score on the seventh day after surgery. Due to a large heterogeneity (P<0.00001, I2=98%, Fig.7) between the studies, So, a random effect model was applied. Our results clearly showed that the MMSE score in DEX group was higher than the control group (SMD=3.28, 95% CI 1.51-5.04, Fig.7). Meta-analysis of these 4 studies indicated that the intraoperative DEX treatment was associated with better postoperative cognitive performance in comparison with saline treated controls on the seventh day after surgery.
Publication Bias
A funnel plot of the 9 studies reporting the incidence of POCD on the third postoperative day was symmetrical, which indicated no publication bias (Figure 8), with all the studies within the 95% CI of the funnel.