The effect of anesthetic depth on postoperative delirium in older adults: a systematic review and meta-analysis

Background Postoperative delirium (POD) is an important complication for older patients and recent randomised controlled trials have showed a conflicting result of the effect of deep and light anesthesia.Methods We included randomised controlled trials including older adults that evaluated the effect of anesthetic depth on postoperative delirium from PubMed, Embase, Web of Science and Cochrane Library. We considered deep anesthesia as observer's assessment of the alertness/ sedation scale (OAA/S) of 0-2 or targeted bispectral (BIS) < 45 and the light anesthesia was considered OAA/S 3-5 or targeted BIS > 50. The primary outcome was incidence of POD within 7 days after surgery. And the secondary outcomes were mortality and cognitive function 3 months or more after surgery. The quality of evidence was assessed via the grading of recommendations assessment, development, and evaluation approach.Results We included 6 studies represented 7736 patients aged 60 years and older. We observed that the deep anesthesia would not increase incidence of POD when compared with the light anesthesia when 4 related studies were pooled (OR, 1.40; 95% CI, 0.63-3.08, P = 0.41, I-2 = 82%, low certainty). And no significant was found in mortality (OR, 1.12; 95% CI, 0.93-1.35, P = 0.23, I-2 = 0%, high certainty) and cognitive function (OR, 1.13; 95% CI, 0.67-1.91, P = 0.64, I-2 = 13%, high certainty) 3 months or more after surgery between deep anesthesia and light anesthesia.Conclusions Low-quality evidence suggests that light general anesthesia was not associated with lower POD incidence than deep general anesthesia. And High-quality evidence showed that anesthetic depth did not affect the long-term mortality and cognitive function.