***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: BACKGROUND Prophylaxis for venous thromboembolism is routinely performed for all patients undergoing bariatric surgery . However , there is disagreement regarding the optimal dosing and duration of anticoagulant therapy . Furthermore , there is little data regarding the incidence of asymptomatic deep venous thrombosis ( DVT ) in this population . Our objective was to conduct a pilot r and omized double blind study to evaluate the pharmacodynamic parameters of 2 different anticoagulation medications ( enoxaparin and fondaparinux ) administered to patients undergoing bariatric surgery . METHODS From July 2010 to August 2013 , 198 consecutive bariatric surgery patients from an academic institution were r and omized in a double blinded manner to receive either 40 mg enoxaparin twice daily or 5 mg fondaparinux sodium once daily . Antifactor Xa activity was measured on all patients in both study arms , 3 hours after the first dose ( on the day of the operation ) , immediately before the second dose ( postoperative day one ) , and 3 hours after the second dose . At the routine 2 week postoperative visit , patients underwent magnetic resonance venography ( MRV ) to detect DVT . The primary outcome was attainment of therapeutic antifactor Xa levels . The secondary outcome was DVT , as detected by MRV . Safety outcomes were perioperative bleeding , perioperative complications , and death . RESULTS Of 198 patients r and omized , 177 underwent MRV and 137 had interpretable antifactor Xa levels . Nearly half of the patients ( 47.4 % ) did not attain target prophylactic antifactor Xa levels . Adequate antifactor Xa levels were more common with fondaparinux ( 74.2 % ) than with enoxaparin ( 32.4 % ) . Antifactor Xa levels were also associated with preoperative D-dimer level . 4 of the 175 patients who underwent MRV developed DVT , 2 in each arm of the study . No major adverse events occurred in either arm . CONCLUSION Fondaparinux was much more likely to produce target prophylactic antifactor Xa levels than enoxaparin . Both regimens appear to be equally effective at reducing the risk of DVT . Further prospect i ve studies are needed to determine the optimal DVT prophylaxis regimen in the bariatric surgical population Background The incidence of venous thromboembolism ( VTE )  after bariatric surgery  is uncertain . Methods Using the re sources of the Rochester Epidemiology Project and the Mayo Bariatric Surgery Registry , we identified all residents of Olmsted County , Minnesota , with incident VTE after undergoing bariatric surgery from 1987 through 2005 . Using the date s of bariatric surgery and VTE events , we determined the cumulative incidence of VTE after bariatric surgery by using the Kaplan – Meier estimator . Cox proportional hazards modeling was used to assess patient age , sex , weight , and body mass index as potential predictors of VTE after bariatric surgery . Results We identified 396 residents who underwent 402 bariatric operations . The most common operation was an open Roux-en-Y gastric bypass ( n = 228 ) . Eight patients had VTE that developed within 6 months ( 7 within 1 month ) after surgery ; five events occurred after hospital discharge but within 1 month after bariatric surgery . The cumulative incidence of VTE at 7 , 30 , 90 , and 180 days was 0.3 , 1.9 , 2.1 , and 2.1 % , respectively ( 180-day 95 % confidence interval ( CI ) , 0.7–3.6 % ) . Patient age was a predictor of postoperative VTE ( hazard ratio , 1.89 per 10-year increase in age ; 95 % CI , 1.01–3.55 ; P = 0.05 ) . Conclusions In our population -based study , bariatric surgery had a high risk of VTE , especially for older patients . Because most VTE events occurred after hospital discharge , a r and omized controlled trial of extended outpatient thromboprophylaxis is warranted in patients undergoing open Roux-en-Y gastric bypass for medically complicated obesity Background Obese patients have a higher risk of venous thromboembolism when immobilized due to surgery . The objective of this study was to assess anti-factor Xa activity in adolescent bariatric surgical patients receiving prophylactic enoxaparin .  Methods Four morbidly obese adolescents undergoing laparoscopic sleeve gastrectomy were enrolled . Enoxaparin was administered ( 40 mg subcutaneous ( SC ) if BMI ≤50 kg/m2 or 60 mg SC if BMI > 50 kg/m2 ) for prevention of venous thromboembolism every 12 h starting after induction of anesthesia until discharge . Plasma anti-factor Xa activity was assessed over 12 h after the first dose and used as a surrogate marker for enoxaparin levels . Non-compartmental analysis of anti-factor Xa activity levels was performed and compared with previously published studies . Results Patients recruited were 16 to 18 years of age with a mean BMI of 52.6 ± 5.8 kg/m2 ( > 99th BMI percentile ) . Peak anti-factor Xa activity ranged from 0.20 to 0.23 IU/mL in our study population , compared to 0.38 to 0.53 IU/mL in the cited lean comparator groups . Conclusions Our current dosing practice of 40 mg SC for individuals with a BMI ≤50 kg/m2 and 60 mg for individuals with a BMI ≥50 kg/m2 result ed in anti-factor Xa activity that was sufficient for adequate thromboprophylaxis in adolescent bariatric surgical patients . Our data also demonstrates lower drug exposures in the obese when compared to lean patients . Therefore , r and omized controlled efficacy and safety studies are urgently needed to guide the use of low-molecular-weight heparins in the pediatric and adolescent obese population BACKGROUND Venous thromboembolism ( VTE ) after laparoscopic bariatric surgery is a significant cause of morbidity and mortality . The objective of the present study was to study the incidence of symptomatic VTE in extended thromboprophylaxis regimens using dalteparin at an independent hospital in Engl and , United Kingdom . METHODS A prospect i ve data base of all patients undergoing bariatric surgery was retrospectively analyzed . All patients underwent VTE prophylaxis regimen using perioperative and extended postoperative low-molecular-weight heparin ( dalteparin 2500 IU preoperatively , followed by 5000 IU daily postoperatively ) . The treatment period was 1 week for laparoscopic gastric b and ing or 3 weeks for all other procedures . Inferior vena cava filters were used in selected patients with thrombophilia , a history of pulmonary embolism , or > 1 episode of deep vein thrombosis . The endpoint was the incidence of symptomatic VTE . RESULTS A total of 735 patients underwent laparoscopic bariatric surgery , all of whom received dalteparin . The postoperative VTE incidence was 0 % . The 30-day and 90-day all-cause mortality rate was 0 % . A total of 3 adverse bleeding events occurred . CONCLUSION An extended VTE prophylaxis regimen using low-molecular-weight heparin is simple and effective and was associated with a low incidence of bleeding complications BACKGROUND The optimal scheme of thromboprophylaxis in bariatric surgery remains uncertain , because clinical practice is different between countries and r and omized trials are lacking . OBJECTIVES The primary objective of this r and omized multicenter study was to determine the optimal regimen of enoxaparin providing an antifactor Xa peak activity between .3 and .5 IU/mL at equilibrium and to evaluate the course of procoagulant microparticles ( MPs ) . SETTING University hospital . METHODS A total of 164 patients scheduled for gastric bypass were allocated to 3 groups ( A , B , and C ) of enoxaparin treatment ( 4000 , 6000 , or 2 × 4000 IU , respectively ) . Antifactor Xa activity  was measured before and 4 hours after each injection from D0 to D2 . Doppler screening of the lower limbs was performed at D1 , D9 , and D30 . Bleeding ( BE ) and thrombotic events ( TE ) were recorded during the first postoperative month . Total MPs were measured at D0 , D9 , and D30 . MPs of leucocyte , platelet , and granulocyte origin were assessed in one third of the patients from each group . The 3 groups were compared by ANOVA . RESULTS A total of 135 patients were analyzed .  The equilibrium of antifactor Xa peak levels was obtained 52 hours after the presurgery injection and 12.8 % , 56.4 % , and 27.3 % of the patients reached the target in groups A , B , and C , respectively ( P<.001 ) . No TE was detected . BE occurred in 1 , 2 , and 6 patients in groups A , B , and C , respectively ) . Total MPs remained unchanged over time . While no significant variation was observed in the other groups , platelet GP1 b(+)-MPs increased ( P = .01 ) at D9 in group C , suggesting an incomplete control of anticoagulation leading to cell activation and procoagulant MP release that was confirmed by the higher MP levels measured at D30 ( P = .04 ) . CD66(+)-MPs were also highly elevated at J9 and D30 in group C indicating a granulocyte contribution . CONCLUSIONS This study shows that a single dose of enoxaparin 6000 IU/d allowed most of the patients to reach the target range of antifactor Xa activity without increasing the bleeding risk , with the most likely efficient reduction of procoagulant MPs . ( Surg Obes Relat Dis 2015;0:000 - 000 . ) © 2015 American Society for Metabolic and Bariatric Surgery . All rights reserved Flaws in the design , conduct , analysis , and reporting of r and omised trials can cause the effect of an intervention to be underestimated or overestimated . The Cochrane Collaboration ’s tool for assessing risk of bias aims to make the process clearer and more Objective : To compare two enoxaparin dosing strategies at achieving prophylactic anti-Xa levels in women with a body mass index ( BMI ) ⩾35 ( kg m−2 ) postcesarean delivery . Study Design : Women with BMI ⩾35 were r and omized to receive prophylactic enoxaparin at a fixed dose of 40 mg daily or weight-based dosing of 0.5 mg kg−1 twice daily . The primary outcome was the proportion of subjects with peak anti-Xa levels in the prophylactic range of 0.2 to 0.6 IU ml−1 . Result : From August 2013 through February 2014 , 84 demographically similar women completed the protocol . In the weight-based group , 88 % ( 37/42 ) of the women reached prophylactic anti-Xa levels versus 14 % ( 6/42 ) in the fixed dose group ( odds ratio 44.4 , 95 % confidence interval 12.44 , 158.48 , P<0.001 ) . No anti-Xa level exceeded 0.48 IU ml−1 . There were no venous thromboembolic or bleeding events requiring reoperation or transfusion in either group . Conclusion : Compared with fixed dosing daily , weight-based dosing twice daily more effectively achieved prophylactic anti-Xa levels without reaching the therapeutic range Background The optimal dose of low molecular weight heparin ( LMWH ) to prevent venous thromboembolism ( VTE ) after bariatric surgery remains controversial . The aim of this multicentre , open-label , pilot study was to evaluate the efficacy and safety of two different doses of the LMWH parnaparin administered to patients undergoing bariatric surgery . Methods Patients were r and omised to receive 4,250 IU/day ( group A ) or 6,400 IU/day ( group B ) of parnaparin s.c . for 7–11 days . Bilateral colour Doppler ultrasound of the lower limb was performed before surgery and at the end of the treatment period . The primary efficacy outcome was a composite of asymptomatic and symptomatic deep vein thrombosis , symptomatic pulmonary embolism and death from any cause during treatment . The primary safety endpoint was major and clinical ly relevant non-major bleeding . Results A total of 258 patients underwent r and omization ; 8 subjects were excluded following the safety analysis . One hundred thirty-one patients [ 106 females ; mean age , 40.3 years ( st and ard deviation ( SD ) ±9.6 ) ; mean body mass index ( BMI ) , 44.6 kg/m2 ( SD ±5.4 ) ] were assigned to group A and 119 patients [ 93 females ; mean age , 41.5 years ( SD ±9.9 ) ; mean BMI , 44.2 kg/m2 ( SD ±5.4 ) ] were assigned to group B.  The rate of the primary efficacy outcome was 1.5 % ( two cases ; 95 % confidence interval ( CI ) , 0.2–6.0 % ) in group A as compared with 0.8 % ( one case ; 95 % CI , 0.4–5.3 % 
    Output:
    
Weight-based and high fixed-dose chemoprophylaxis regimens achieved target anti-Xa concentrations more frequently than st and ard fixed-dose regimens but were not associated with a reduction in VTE .
Additionally , high fixed-dose approaches are associated with increased bleeding complications .