Depth Of Anesthesia Measured By Bispectral Index And Postoperative Mortality: A Meta-analysis Of Observational Studies

Introduction: For patients that receive general anesthesia,both early(30 days)and extended(<5 year)mortality can be very important.This can be the result of many different factors affecting survival,both relating to the operation and to the patient themselves.However,many studies used only qualitative analyses to draw conclusions,making it uncertain as to whether depth of anesthesia plays a significant role in postoperative mortality and other outcomes.This meta-analysis sought to explore the relationship between depth of anesthesia(based on BIS)and postoperative mortality using available published literature.Methods: Several databases(PUBMED,EMBASE,OVID and the Cochrane library databases)were systematically searched to identify all articles studying the relationship between depth of anesthesia and postoperative mortality.Only those studies that assessed the link between BIS and mortality were included,and only if those studies further were observational studies using multivariate Cox proportional regression modeling with an adjusted hazard ratio(aHR)available.Pooled aHR values and corresponding 95% confidence intervals(CIs)were estimated as a measure of the link between postoperative mortality and depth of anesthesia.Forest plots of these estimated values were generated following subgroup analyses.Post hoc subgroup analyses were conducted for follow-up period(30 days vs.longer than 90 days)and type of surgery(cardiac surgery vs.non-cardiac surgery).Results: The analysis included 38,722 patients from nine studies.We detected a significant relationship between overall mortality and low BIS values(pooled aHR,1.22;95% CI,1.08 to 1.38;P = 0.001;I2=85.4%;P < 0.001).We found no significant link between BIS and mortality when follow-up duration were 30 days or less by post hoc subgroup analysis(n = 12,713;pooled aHR,1.52;95% CI,0.97 to 2.38;P = 0.28;I2 =79.0%;P < 0.001).When the follow-up duration was ?90 days,however,this relationship between low BIS and mortality was significant(n = 26,009;pooled aHR,1.09;95% CI,1.00 to 1.19;P = 0.01;I2 = 79.4%;P < 0.001).Another post hoc subgroup analysis demonstrated a significant relationship between low BIS and mortality in patients with cardiac surgery(n = 2,650;pooled aHR,1.30;95% CI,1.14 to 1.49;P <0.001;I2 =0.0%;P = 0.611).However,in those patients who had undergone non-cardiac-related surgery this link was not significant(n = 22,887;pooled aHR,1.06;95% CI,0.98 to 1.14;P = 0.14;I2 =73.2%;P = 0.011).Conclusions: In conclusion,by pooling published observational studies there appears to be a significant link between low BIS values(as a readout for depth of anesthesia)and long-term mortality,although this relationship failed to achieve significance 30 days after surgery,based on the available data.In cardiac surgery patients,deep anesthesia may increase postoperative mortality.However,we did not find this trend in non-cardiac surgery patients.This analysis suggests that patients may benefit if excessive depth of anesthesia were avoided.By further exploring the long-term effects of acute care,our results may provide a reference for patient care in clinical applications.