***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: This study considered if N-terminal prohormone brain natriuretic peptide ( NT-proBNP ) is associated with increased risk for postoperative cardiac events in high-risk patients undergoing noncardiac surgery .  In addition , this report describes how levels of NT-proBNP are affected by noncardiac surgery . The study design was a prospect i ve cohort study that enrolled 83 patients age > or = 50 years with > or = 1 risk factor for coronary artery disease having intermediate or high-risk noncardiac surgery .  NT-proBNP levels  were measured preoperatively and on postoperative days 1 and 3 . During the month following surgery , 25 patients ( 33 % ) had a combined 37 postoperative cardiac events including 15 episodes of heart failure ( 20 % ) , 12 episodes of new dysrhythmia ( 16 % ) , 7 myocardial infa rct ions ( 9 % ) , and 3 cardiac arrests ( 4 % ) . Preoperative NT-proBNP level > or = 457 pg/ml was significantly associated with occurrence of a postoperative cardiac event ( odds ratio 10.5 , 95 % confidence interval 1.9 to 56.6 , p = 0.006 ) . After surgery , 64 of 72 patients ( 89 % ) had an increase in NT-proBNP from their preoperative level . In conclusion , this study determined there was a significant association between elevated preoperative NT-proBNP and occurrence of a postoperative cardiac event . In addition , increased NT-proBNP after noncardiac surgery is not uncommon even in the absence of clinical ly identifiable heart failure Background — Postoperative atrial fibrillation  ( AF ) is a complication of thoracic surgery for lung cancer , with a reported incidence that can run as high as 42 % . Recently , it has been observed retrospectively that B-type natriuretic peptide predicts AF after cardiac surgery . We performed a prospect i ve study to evaluate the role of N-terminal pro-B-type natriuretic peptide ( NT-proBNP ) as a marker for risk stratification of postoperative AF in patients undergoing thoracic surgery for lung cancer . Methods and Results — We measured NT-proBNP levels in 400 patients ( mean age , 62±10 years ; 271 men ) 24 hours before and 1 hour after surgery . The primary end point of the study was the incidence of postoperative AF . Overall , postoperative AF occurred in 72 patients ( 18 % ) . Eighty-eight patients ( 22 % ) showed an elevated perioperative NT-proBNP value . When patients with either preoperatively or postoperatively elevated NT-proBNP were pooled , a greater incidence of AF was observed compared with patients with normal values ( 64 % versus 5 % ; P<0.001 ) . At multivariable analysis , adjusted for age , gender , major comorbidities , echocardiography parameters , pneumonectomy , and medications , both preoperative and postoperative NT-proBNP values were independent predictors of AF ( relative risk , 27.9 ; 95 % CI , 13.2 to 58.9 ; P<0.001 for preoperative NT-proBNP elevation ; relative risk , 20.1 ; 95 % CI , 5.8 to 69.4 ; P<0.001 for postoperative NT-proBNP elevation ) . Conclusions — Elevation of perioperative NT-proBNP is a strong independent predictor of postoperative AF in patients undergoing thoracic surgery for lung cancer . This finding should facilitate studies of therapies to reduce AF in selected high-risk patients Background — Volatile anesthetics provide myocardial preconditioning in coronary surgery patients . We hypothesized that sevoflurane compared with propofol reduces the incidence of myocardial ischemia in patients undergoing major noncardiac surgery . Methods and Results — We enrolled 385 patients at cardiovascular risk in 3 centers . Patients were r and omized to maintenance of anesthesia with sevoflurane or propofol .  We recorded continuous ECG for 48 hours perioperatively , measured troponin T and N-terminal prohormone of brain natriuretic peptide ( NT-proBNP ) on postoperative days 1 and 2 , and evaluated postoperative delirium by the Confusion Assessment Method . At 6 and 12 months , we contacted patients by telephone to assess major adverse cardiac events . The primary end point was a composite of myocardial ischemia detected by continuous ECG and /or troponin elevation . Additional end points were postoperative NT-proBNP concentrations , major adverse cardiac events , and delirium . Patients and outcome assessors were blinded . We tested dichotomous end points by & khgr;2 test and NT-proBNP by Mann – Whitney test on an intention-to-treat basis . Myocardial ischemia occurred in 75 patients ( 40.8 % ) in the sevoflurane and 81 ( 40.3 % ) in the propofol group ( relative risk , 1.01 ; 95 % confidence interval , 0.78–1.30 ) . NT-proBNP release did not differ across allocation on postoperative day 1 or 2 . Within 12 months , 14 patients ( 7.6 % ) suffered a major adverse cardiac event after sevoflurane and 17 ( 8.5 % ) after propofol ( relative risk , 0.90 ; 95 % confidence interval , 0.44–1.83 ) . The incidence of delirium did not differ ( 11.4 % versus 14.4 % ; P=0.379 ) . Conclusions — Compared with propofol , sevoflurane did not reduce the incidence of myocardial ischemia in high-risk patients undergoing major noncardiac surgery . The sevoflurane and propofol groups did not differ in postoperative NT-proBNP release , major adverse cardiac events at 1 year , or delirium . Clinical Trial Registration — URL : http://www . clinical trials.gov . Unique identifier : NCT00286585 We performed a Monte Carlo study to evaluate the effect of the number of events per variable ( EPV ) analyzed in logistic regression analysis . The simulations were based on data from a cardiac trial of 673 patients in which 252 deaths occurred and seven variables were cogent predictors of mortality ; the number of events per predictive variable was ( 252/7 =) 36 for the full sample . For the simulations , at values of EPV = 2 , 5 , 10 , 15 , 20 , and 25 , we r and omly generated 500 sample s of the 673 patients , chosen with replacement , according to a logistic model derived from the full sample . Simulation results for the regression coefficients for each variable in each group of 500 sample s were compared for bias , precision , and significance testing against the results of the model fitted to the original sample . For EPV values of 10 or greater , no major problems occurred . For EPV values less than 10 , however , the regression coefficients were biased in both positive and negative directions ; the large sample variance estimates from the logistic model both overestimated and underestimated the sample variance of the regression coefficients ; the 90 % confidence limits about the estimated values did not have proper coverage ; the Wald statistic was conservative under the null hypothesis ; and paradoxical associations ( significance in the wrong direction ) were increased . Although other factors ( such as the total number of events , or sample size ) may influence the validity of the logistic model , our findings indicate that low EPV can lead to major problems BACKGROUND : Associations between preoperative elevation of brain natriuretic peptide ( BNP ) or postoperative elevation of cardiac troponins ( cTn ) with major adverse cardiac events ( MACE ) after major surgery have been shown previously . In this study , we evaluated the added value of preoperative BNP with postoperative cTn levels for the prediction of MACE in patients undergoing major vascular surgery . METHODS : This is a prospect ively prespecified , secondary analysis of data from a cohort of 133 clinical ly stable patients undergoing major vascular surgery enrolled in a clinical trial evaluating the effectiveness of the sympathetic nervous system-inhibiting drug moxonidine on reducing MACE . Concentrations of BNP and cTn  were determined before surgery , and concentrations of  cTn  were measured immediately after surgery and on postoperative days 1 , 2 , 3 , and 7 . The primary end point was the occurrence of MACE ( defined as any hospitalization for myocardial revascularization , acute coronary syndrome , acute congestive heart failure , or death by any cause ) within 1 yr after surgery . Patients were evaluated for MACE by hospital chart review during hospitalization and by telephone interviews 12 mo after surgery . RESULTS : Within 1 yr after surgery , 19 patients ( 14 % ) had a MACE , including 14 patients ( 11 % ) who died . After adjustment for age , gender , and the revised cardiac risk index , preoperative BNP elevation ≥50 pg/mL was associated with MACE ( adjusted hazard ratio [ HR ] : 6.5 , 95 % confidence interval [ CI ] : 1.4–29.5 ) regardless of the subsequent cTn I concentrations . The combination of preoperative BNP elevation ≥50 pg/mL and postoperative cTn I elevation ≥2 ng/mL was associated with MACE ( adjusted HR : 25.2 , 95 % CI : 5.0–128.4 ) and all-cause mortality ( adjusted HR : 18.7 , 95 % CI : 3.1–112.5 ) . The negative predictive value of a normal preoperative BNP value for subsequent adverse events was 0.965 ( 95 % CI : 0.879–0.996 ) . CONCLUSION : These data suggest that measurement of preoperative BNP concentrations in addition to postoperative cTn concentrations provides additive prognostic information for MACE and mortality after major vascular surgery Background :  Postoperative cognitive dysfunction ( POCD ) is a significant cause of morbidity after noncardiac surgery . Identified risk factors are largely limited to demographic characteristics . We hypothesized that POCD was associated with apolipoprotein E4 ( APOE4 ) genotype and plasma biomarkers of brain injury and inflammation . Methods : Three hundred ninety-four patients older than 55 yr undergoing major elective noncardiac surgery were enrolled in this prospect i ve observational study . Apolipoprotein E genotyping was performed at baseline . Plasma was collected at baseline and end of surgery and at 4.5 , 24 , and 48-h postoperatively . Six protein biomarkers were assayed ( B-type natriuretic peptide , C-reactive protein , D-dimer , matrix metalloproteinase-9 , neuron-specific enolase , and S-100B ) . Neurocognitive testing was conducted at baseline and at 6 weeks and 1 yr after surgery ; scores were subjected to factor analysis . The association of APOE4 and biomarkers with POCD was tested using multivariable regression modeling . Results : Three hundred fifty patients ( 89 % ) completed 6-week neurocognitive testing . POCD occurred in 54.3 % of participants at 6 weeks and 46.1 % at 1 yr . There was no difference in POCD between patients with or without the APOE4 allele ( 56.6 vs. 52.6 % ; P = 0.58 ) . The continuous cognitive change score ( mean ± SD ) was similar between groups ( APOE4 : 0.05 ± 0.27 vs. non-APOE4 : 0.07 ± 0.28 ; P = 0.53 ) . Two hundred ninety-one subjects ( 74 % ) completed testing at 1 yr . POCD occurred in 45.9 % of APOE4 subjects versus 46.3 % of non-APOE4 subjects ( P = 0.95 ) . The cognitive score was again similar ( APOE4 : 0.08 ± 0.27 vs. non-APOE4 : 0.05 ± 0.25 ; P = 0.39 ) . Biomarker levels were not associated with APOE4 genotype or cognition at 6 weeks or 1 yr . Conclusion : Cognitive decline after major noncardiac surgery is not associated with APOE4 genotype or plasma biomarker levels OBJECTIVES To determine if troponin I and NT-proBNP were predictors of 6-month mortality after emergency  orthopedic-geriatric surgery in a frail population . DESIGN Prospect i ve observational study . SETTING Orthopedic-geriatric unit of a metropolitan hospital in Australia . PARTICIPANTS A total of 383 patients were screened ; 44 were eligible for this study of which 33 patients consented who were receiving high-level care or had severe dementia or an illness with a prognosis of less than 12 months . MEASUREMENTS  Troponin I and NT-proBNP  were tested on one preoperative sample and at least one postoperative blood sample . Cardiac events were defined as acute myocardial infa rct ion , congestive cardiac failure , new onset or rapid atrial fibrillation , major arrhythmia , or cardiac arrest . RESULTS The mean age of the patients was 85.8 + /- 9.6 years and 93.9 % had 
    Output:
    
Additional post-operative NP measurement enhanced risk stratification for the composite outcomes of death or nonfatal myocardial infa rct ion at 30 days and ≥180 days after noncardiac surgery compared with a pre-operative NP measurement alone