You will be presented with a collection of medical randomized controlled trial (RCT) reports addressing a shared clinical question -- for instance, the efficacy of a medical intervention on a disease or condition. Given the titles and abstracts of these reports, your task is to generate the conclusion of the systematic review article synthesizing the key findings. Your conclusion should be a few sentences long. In your response, include only the conclusion and no other text. The RCT reports are below.



Title 1:
An Introduction to Propensity Score Methods for Reducing the Effects of Confounding in Observational Studies
Abstract 1:
The propensity score is the probability of treatment assignment conditional on observed baseline characteristics . The propensity score allows one to design and analyze an observational ( nonr and omized ) study so that it mimics some of the particular characteristics of a r and omized controlled trial . In particular , the propensity score is a balancing score : conditional on the propensity score , the distribution of observed baseline covariates will be similar between treated and untreated subjects . I describe 4 different propensity score methods : matching on the propensity score , stratification on the propensity score , inverse probability of treatment weighting using the propensity score  , and covariate adjustment using the propensity score . I describe balance diagnostics for examining whether the propensity score model has been adequately specified . Furthermore , I discuss differences between regression-based methods and propensity score-based methods for the analysis of observational data . I describe different causal average treatment effects and their relationship with propensity score analyses


Title 2:
Prevention of Intraoperative Awareness with Explicit Recall in an Unselected Surgical Population: A Randomized Comparative Effectiveness Trial
Abstract 2:
Background : Intraoperative awareness with explicit recall occurs in approximately 0.15 % of all surgical cases . Efficacy trials based on the Bispectral Index ® ( BIS ) monitor ( Covidien , Boulder , CO ) and anesthetic concentrations have focused on high-risk patients , but there are no effectiveness data applicable to an unselected surgical population . Methods : We conducted a r and omized controlled trial of unselected surgical patients at three hospitals of a tertiary academic medical center . Surgical cases were r and omized to alerting algorithms based on either BIS values or anesthetic concentrations . The primary outcome was the incidence of definite intraoperative awareness ; prespecified secondary outcomes included postanesthetic recovery variables . Results : The study was terminated because of futility . At interim analysis the incidence of definite awareness was 0.12 % ( 11/9,376 ) ( 95 % CI : 0.07–0.21 % ) in the anesthetic concentration group and 0.08 % ( 8/9,460 ) ( 95 % CI : 0.04–0.16 % ) in the BIS group ( P = 0.48 ) . There was no significant difference between the two groups in terms of meeting criteria for recovery room discharge or incidence of nausea and vomiting . By post hoc secondary analysis , the BIS protocol was associated with a 4.7-fold reduction in definite or possible awareness events compared with a cohort receiving no intervention ( P = 0.001 ; 95 % CI : 1.7–13.1 ) . Conclusion : This negative trial could not detect a difference in the incidence of definite awareness or recovery variables between monitoring protocol s based on either BIS values or anesthetic concentration . By post hoc analysis , a protocol based on BIS monitoring reduced the incidence of definite or possible intraoperative awareness compared with routine care


Title 3:
Broadly Applicable Risk Stratification System for Predicting Duration of Hospitalization and Mortality
Abstract 3:
Background : Hospitals are increasingly required to publicly report outcomes , yet performance is best interpreted in the context of population and procedural risk . We sought to develop a risk-adjustment method using administrative cl aims data to assess both national-level and hospital-specific performance . Methods : A total of 35,179,507 patient stay records from 2001–2006 Medicare Provider Analysis and Review ( MEDPAR ) files were r and omly divided into development and validation sets . Risk stratification indices ( RSIs ) for length of stay and mortality endpoints were derived from aggregate risk associated with individual diagnostic and procedure codes . Performance of RSIs were tested prospect ively on the validation data base , as well as a single institution registry of 103,324 adult surgical patients , and compared with the Charlson comorbidity index , which was design ed to predict 1-yr mortality . The primary outcome was the C statistic indicating the discriminatory power of alternative risk-adjustment methods for prediction of outcome measures . Results : A single risk-stratification model predicted 30-day and 1-yr postdischarge mortality ; separate risk-stratification models predicted length of stay and in-hospital mortality . The RSIs performed well on the national data set ( C statistics for median length of stay and 30-day mortality were 0.86 and 0.84 ) . They performed significantly better than the Charlson comorbidity index on the Clevel and Clinic registry for all outcomes . The C statistics for the RSIs and Charlson comorbidity index were 0.89 versus 0.60 for median length of stay , 0.98 versus 0.65 for in-hospital mortality , 0.85 versus 0.76 for 30-day mortality , and 0.83 versus 0.77 for 1-yr mortality . Addition of demographic information only slightly improved performance of the RSI . Conclusion : RSI is a broadly applicable and robust system for assessing hospital length of stay and mortality for groups of surgical patients based solely on administrative data


Title 4:
Mortality Within 2 Years After Surgery in Relation to Low Intraoperative Bispectral Index Values and Preexisting Malignant Disease
Abstract 4:
BACKGROUND : A correlation between deep anesthesia ( defined as time with Bispectral Index ( BIS ) < 45 ; TBIS < 45 ) and death within 1 yr after surgery has previously been reported . In order to confirm or refute these findings , we evaluated TBIS < 45 as an independent risk factor for death within 1 and 2 yr after surgery and also the impact of malignancy , the predominant cause of death in the previous report . METHODS : Mortality within 2 yr after surgery , causes of death and the occurrence of malignant disease at the time of surgery were identified in a cohort of 4087 BIS-monitored patients . Statistically significant univariate predictors of mortality were identified . In order to allow for comparison with previous data , the following multivariate analysis was first done without , and thereafter with , preexisting malignancy status , the predominant cause of death . RESULTS : One-hundred-seventy-four ( 4.3 % ) patients died within 1 yr and another 92 during the second year ( totaling 6.5 % in 2 yr ) . TBIS < 45 was a significant predictor of 1- and 2-yr mortality when preexisting malignant disease was not among the co-variates ( hazard ratio [ HR ] 1.13 [ 1.01–1.27 ] and 1.18 [ 1.08–1.29 ] , respectively ) . Further exploration confined the significant relation between postoperative mortality and TBIS < 45 to patients with preexisting malignant diagnoses associated with extensive surgery and less favorable prognosis . The most powerful predictors of 2-yr mortality in the model , including preexisting malignancy , were ASA physical score class IV ( HR 19.3 [ 7.31–51.1 ] ) , age > 80 yr ( HR 2.93 [ 1.79–4.79 ] ) , and preexisting malignancy associated with less favorable prognosis ( HR 9.30 [6.60–13.1]).When the initial multivariate regression was repeated using preexisting malignancy status among the co-variates in the model , the previously significant relation between 1 , and 2-yr mortality and TBIS < 45 did not reach statistical significance . CONCLUSION : Using a similar set of co-variates as in previous work , we confirmed the statistical relation between 1-yr mortality and TBIS < 45 , and we extended this observation to 2-yr mortality . However , this relation is sensitive to the selection of co-variates in the statistical model , and a r and omized study is required to demonstrate that there really is a causal impact from and TBIS < 45 on postoperative mortality and , if it does , the effect is probably very weak in comparison with co-morbidity as assessed by ASA physical score , the preexisting malignancy status at surgery and age


Title 5:
Prevention of intraoperative awareness in a high-risk surgical population.
Abstract 5:
BACKGROUND Unintended intraoperative awareness , which occurs when general anesthesia is not achieved or maintained , affects up to 1 % of patients at high risk for this complication . We tested the hypothesis that a protocol incorporating the electroencephalogram-derived bispectral index ( BIS ) is superior to a protocol incorporating st and ard monitoring of end-tidal anesthetic-agent concentration ( ETAC ) for the prevention of awareness . METHODS We conducted a prospect i ve , r and omized , evaluator-blinded trial at three medical centers . We r and omly assigned 6041 patients at high risk for awareness to BIS-guided anesthesia  ( with an audible alert if the BIS value was < 40 or > 60 , on a scale of 0 to 100 , with 0 indicating the suppression of detectable brain electrical activity and 100 indicating the awake state ) or ETAC-guided anesthesia ( with an audible alert if the ETAC was < 0.7 or > 1.3 minimum alveolar concentration ) . In addition to audible alerts , the protocol s included structured education and checklists . Superiority of the BIS protocol was assessed with the use of a one-sided Fisher 's exact test . RESULTS A total of 7 of 2861 patients ( 0.24 % ) in the BIS group , as compared with 2 of 2852 ( 0.07 % ) in the ETAC group , who were interviewed postoperatively had definite intraoperative awareness ( a difference of 0.17 percentage points ; 95 % confidence interval [ CI ] , -0.03 to 0.38 ; P=0.98 ) . Thus , the superiority of the BIS protocol was not demonstrated . A total of 19 cases of definite or possible intraoperative awareness ( 0.66 % ) occurred in the BIS group , as compared with 8 ( 0.28 % ) in the ETAC group ( a difference of 0.38 percentage points ; 95 % CI , 0.03 to 0.74 ; P=0.99 ) , with the superiority of the BIS protocol again not demonstrated . There was no difference between the groups with respect to the amount of anesthesia administered or the rate of major postoperative adverse outcomes . CONCLUSIONS The superiority of the BIS protocol was not established ; contrary to expectations , fewer patients in the ETAC group than in the BIS group experienced awareness . ( Funded by the Foundation for Anesthesia Education and Research and others ; BAG-RECALL Clinical Trials.gov number , NCT00682825 . )


Title 6:
Anesthetic Management and One-Year Mortality After Noncardiac Surgery
Abstract 6:
Little is known about the effect of anesthetic management on long-term outcomes . We design ed a prospect i ve observational study of adult patients undergoing major noncardiac surgery with general anesthesia  to determine if mortality in the first year after surgery is associated with demographic , preoperative clinical , surgical , or intraoperative variables .  One-year mortality was 5.5 % in all patients ( n = 1064 ) and 10.3 % in patients ≥65 yr old ( n = 243 ) . Multivariate Cox Proportional Hazards modeling identified three variables as significant independent predictors of mortality : patient comorbidity ( relative risk , 16.116 ; P < 0.0001 ) , cumulative deep hypnotic time ( Bispectral Index ® < 45 ) ( relative risk = 1.244/h ; P = 0.0121 ) and intraoperative systolic hypotension ( relative risk = 1.036/min ; P = 0.0125 ) . Death during the first year after surgery is primarily associated with the natural history of preexisting conditions . However , cumulative deep hypnotic time and intraoperative hypotension were also significant , independent predictors of increased mortality . These associations suggest that intraoperative anesthetic management may affect outcomes over longer time periods than previously appreciated


Title 7:
The Effect of Bispectral Index Monitoring on Long-Term Survival in the B-Aware Trial
Abstract 7:
BACKGROUND : When anesthesia is titrated using bispectral index ( BIS ) monitoring , patients generally receive lower doses of hypnotic drugs . Intraoperative hypotension and organ toxicity might be avoided if lower doses of anesthetics are administered , but whether this translates into a reduction in serious morbidity or mortality remains controversial . The B-Aware Trial r and omly allocated 2463 patients at high risk of awareness to BIS-guided anesthesia or routine care .  We tested the hypothesis that the risks of death , myocardial infa rct ion ( MI ) , and stroke would be lower in patients allocated to BIS-guided management than in those allocated to routine care . METHODS : The medical records of all patients who had not died within 30 days of surgery were review ed . The date and cause of death and occurrence of MI or stroke were recorded . A telephone interview was then conducted with all surviving patients . The primary end point of the study was survival . RESULTS : The median follow-up time was 4.1 ( range : 0–6.5 ) years . Five hundred forty-eight patients ( 22.2 % ) had died since the index surgery , 220 patients ( 8.9 % ) had an MI , and 115 patients ( 4.7 % ) had a stroke . The risk of death in BIS patients was not significantly different than in routine care patients ( hazard ratio = 0.86 [ 95 % confidence interval { CI } : 0.72–1.01 ] ; P = 0.07 ) . However , propensity score analysis indicated that the hazard ratio for death in patients who recorded BIS values < 40 for > 5 min compared with other BIS-monitored patients was 1.41 ( 95 % CI : 1.02–1.95 ; P = 0.039 ) . In addition , the odds ratios for MI in patients who recorded BIS values < 40 for > 5 min compared with other BIS-monitored patients was 1.94 ( 95 % CI : 1.12–3.35 ; P = 0.02 ) and the odds ratio for stroke was 3.23 ( 95 % CI : 1.29–8.07 ; P = 0.01 ) . CONCLUSIONS : Monitoring with BIS and absence of BIS values < 40 for > 5 min were associated with improved survival and reduced morbidity in patients enrolled in the B-Aware Trial
Conclusion The present study demonstrated that patients exposed to the triple low state exhibit higher 30-day mortality rates than those not exposed to the triple low state