The correlation of the depth of anesthesia and postoperative cognitive impairment: A meta-analysis based on randomized controlled trials

To comprehensively evaluate the associations between the depth of anesthesia and postoperative delirium (POD) or postoperative cognitive dysfunction (POCD).Using the Cochrane evaluation system, the included studies were conducted with quality assessment.We searched Cochrane library, Embase and PubMed databases without language restriction. The retrieval time is up to August 2017.According to the PRISMA guideline, the results associated with POCD and POD separately were compared between low and high bispectral index (BIS) groups under fixed effects model or random effects model. Besides, the risk ratio (RR) and 95% confidence intervals (95% CIs) were utilized as the effect sizes for merging the results. Furthermore, sensitivity analysis was performed to evaluate the stability of the results. Using Egger's test, publication bias was assessed for the included studies.Totally, 4 studies with high qualities were selected for this meta-analysis. The merged results of POCD showed no significant difference between low and high BIS groups (RR (95% CI)=0.84 (0.21, 3.45), P>0.05). Sensitivity analysis showed that the merged results of POCD were not stable (RR (95%CI)=0.41 (0.17, 0.99)-1.88 (1.09, 3.22), P=0.046). Additionally, no significant publication bias for POCD was found (P=0.385).There was no significant correlation between the depth of anesthesia and POCD.