***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 
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    Input: Background Although aspirin therapy started before operation improves vein graft patency after coronary artery bypass grafting , it also causes bleeding . The objective of this prospect i ve , central ly directed , r and omized , double-blind , placebo-controlled trial was to compare the effects of aspirin therapy started before operation with aspirin started 6 hours after operation on early ( 7–10-day ) graft patency . Methods and Results Patients were r and omized to receive either aspirin 325 mg or placebo the night before surgery ; after operation , all patients received aspirin 325 mg daily , with the first dose administered through the nasogastric tube 6 hours after operation . Angiography was performed in 72 % of the analyzed patients an average of 8 days after operation , and the primary end point was saphenous vein graft patency in 351 patients . Internal mammary artery graft patency was also assessed in 246 patients because many individuals received both internal mammary artery and vein grafts . In the patients given preoperative aspirin , the vein graft occlusion rate was 7.4 ± 1.3 % compared with 7.8 ± 1.5 % in those who received preoperative placebo ( p = 0.871 ) . In the subgroup of patients receiving Y grafts , 0.0 % of the grafts were occluded in the preoperative aspirin group compared with 7.0 ± 3.6 % in the preoperative placebo group ( p = 0.066 ) . The internal mammary artery occlusion rate was 0.0 % ( 0 of 131 ) in the aspirin group compared with 2.4 ± 1.4 % ( three of 125 ) in the placebo group ( p = 0.081 ) . Patients in the aspirin group received more transfusions than those in the placebo group ( median , 900 versus 725 ml , p=0.006 ) . The reoperation rate for bleeding in the aspirin group was 6.3 % compared with 2.4 % in the placebo group ( p = 0.036 ) . Median chest tube drainage within the first 6 hours after operation was 500 ml in the aspirin group compared with 448 ml in the placebo group ( p = 0.011 ) . Conclisions . Thus , preoperative aspirin is associated with increased bleeding complications and offers no additional benefit in early vein graft patency compared with starting aspirin therapy 6 hours after operation . There was a trend , although not significant , toward improved early patency for Y grafts and internal mammary artery grafts with preoperative aspirin AIM Renal function is one of the most important prognostic factors following cardiac surgery . Whether aspirin affects cardiopulmonary bypass related renal injury is investigated in this study . METHODS Ninety-four patients with impaired renal function ( creatinine = or > 1.5 mg/dl ) undergoing coronary artery bypass grafting ( CABG )  were categorized into 2 groups according to aspirin administration before surgery . Serum creatinine , urinary output and creatinine clearance along with other perioperative factors were compared between the 2 groups prior to surgery , 24 hours and 48 hours following cardiopulmonary bypass . RESULTS Creatinine levels increased significantly in the second postoperative day only in the non-aspirin ( control ) group ( 3.7+/-1.6 vs 2.9+/-1.7 mg/dl , p=0.03 ) . Aspirin ( study ) group had lower creatinine levels in day 1 ( p=0.03 ) and day 2 ( p=0.001 ) . Furthermore , in the study group creatinine clearance was higher in day 1 ( 34.3+/-14.3 vs 30.9+/-13.1 ml/min , p=0.01 ) and in day 2 ( 32.6+/-13.8 vs 26.4+/-9.8 ml , p<0.0001 ) . Creatinine levels at discharge were elevated compared to the preoperative levels in the control group ( p=0.01 ) . However , the study group had lower creatinine levels at discharge ( 2.6+/-1.4 vs 3.8+/-1.6 mg/dl , p<0.0001 ) . Urinary output was higher in the study group in the first postoperative day compared to the control group ( p=0.01 ) . Postoperative bleeding was slightly increased in the study group compared to the control group ( 760+/-230 ml vs 530+/-210 ml , p=0.01 ) . CONCLUSIONS Continuation of aspirin administration until the day of surgery may have a protective effect against renal injury result ing from cardiopulmonary bypass , with only a negligible increase in bleeding . Possible explanations for this effect are antiplatelet activity of aspirin during cardiopulmonary bypass causing inhibition of vasoconstrictive agents like thromboxane , and improvement of renal perfusion by reducing blood viscosity Background —Aspirin is beneficial in the setting of atherosclerotic cardiovascular disease . There are limited data evaluating preoperative aspirin administration preceding coronary artery bypass grafting and associated postoperative outcomes . Methods and Results —Using prospect ively collected data from 1636 consecutive patients undergoing first-time isolated coronary artery bypass surgery at our institution from January 2000 through December 2002 , we evaluated the association between aspirin usage within the 5 days preceding coronary bypass surgery and risk of adverse in-hospital postoperative events . A logistic regression model , which included propensity scores , was used to adjust for remaining differences between groups . Overall , there were 36 deaths ( 2.2 % ) and 48 adverse cerebrovascular events ( 2.9 % ) in the postoperative hospitalization period . Patients receiving preoperative aspirin ( n=1316 ) had significantly lower postoperative in-hospital mortality compared with those not receiving preoperative aspirin [ 1.7 % versus 4.4 % ; adjusted odds ratio ( OR ) , 0.34 ; 95 % CI , 0.15 to 0.75 ; P=0.007 ] . Rates of postoperative cerebrovascular events were similar between groups ( 2.7 % versus 3.8 % ; adjusted OR , 0.67 ; 95 % CI , 0.32 to 1.50 ; P=0.31 ) . Preoperative aspirin therapy was not associated with an increased risk of reoperation for bleeding ( 3.5 % versus 3.4 % ; P=0.96 ) or requirement for postoperative blood product transfusion ( adjusted OR , 1.17 ; 95 % CI , 0.88 to 1.54 ; P=0.28 ) . Conclusions —Aspirin usage within the 5 days preceding coronary artery bypass surgery is associated with a lower risk of postoperative in-hospital mortality and appears to be safe without an associated increased risk of reoperation for bleeding or need for blood product transfusion BACKGROUND We tried to evaluate the clinical outcomes ( mortality , postoperative bleeding and perioperative myocardial infa rct ion ) of patients who underwent first elective coronary artery bypass grafting and received aspirin during the preoperative period . METHODS The study was a prospect i ve , r and omized and single-blinded clinical trial . Two hundred patients were included and divided into two groups . One group received aspirin 80 - 160 mg , while in the other aspirin was stopped at least seven days before surgery . The primary end-points of the study were in-hospital mortality and hemorrhage-related complications ( postoperative blood loss in the intensive care unit , re-exploration for bleeding and red blood cell and non-red blood cell requirements ) . The secondary end-point was perioperative myocardial infa rct ion . RESULTS There were no differences in patient characteristics between the aspirin users and non-aspirin users . We found a significant difference between postoperative blood loss ( 608 + /- + /- 359.7 ml vs. 483 + /- 251.5 ml ; p = 0.005 ) and red blood cell product requirements ( 1.32 + /- + /- 0.97 unit packed cell vs. 0.94 + /- 1.02 unit packed cell ; p = 0.008 ) . There was no significant difference between the two groups regarding platelet requirement and the rate of in-hospital mortality and re-exploration for bleeding . Similarly , we found no significant difference in the incidence of definite and probable perioperative myocardial infa rct ion ( p = 0.24 and p = 0.56 respectively ) or in-hospital mortality between the two groups . CONCLUSION Preoperative aspirin administration increased postoperative bleeding and red blood cell requirements with no effect on mortality , re-exploration rate and perioperative myocardial infa rct ion . We recommend withdrawal of aspirin seven days prior to surgery . ( Cardiol J 2007 ; 14 : 453 - 457 ) 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 Patients undergoing aortocoronary bypass using autogenous saphenous veins were r and omly divided into three comparable groups . Group 1 ( n = 10 ) acted as a control , Group 2 ( n = 14 ) received 80 mg of aspirin at midnight before the operation , and Group 3 ( n = 12 ) received 80 mg of aspirin and 75 mg of dipyridamole at midnight and an additional 75-mg dose of dipyridamole at 6 AM . The purpose was to determine which regimen would maximally inhibit platelet function without depressing vascular prostacyclin synthesis . Serum thromboxane A2 , saphenous vein wall and aortic wall prostacyclin , platelet aggregation , and bleeding time were measured in all patients . None was restarted on a regimen of aspirin or dipyridamole postoperatively . Aspirin alone and in combination with dipyridamole significantly inhibited thromboxane A2 and platelet aggregation in all treated patients but spared venous prostacyclin synthesis . Aortic prostacyclin synthesis was partially inhibited in both treated groups . Chest tube drainage was comparable in all three groups . These results indicate that the combination of aspirin and dipyridamole offers no measurable advantage over aspirin alone in the perioperative period OBJECTIVES Release of thromboxane ( Tx ) A(2 ) by platelets may be one of multiple factors that are responsible for lung injury after cardiopulmonary bypass , leading to pulmonary vasoconstriction and impaired oxygenation . In experimental models , the inhibition of Tx receptor or its production improved lung function . The use of aspirin , which is used widely in the treatment of ischemic heart disease because of its antiplatelet activity , is usually discontinued a week before the patient undergoes the operation to restore normal platelet hemostatic function . The purpose of this study was to determine the relationship between the time of cessation of aspirin before coronary artery bypass surgery , and postoperative oxygenation and bleeding . DESIGN A prospect i ve clinical study comparing the effect of aspirin on postoperative oxygenation in patients who had been treated or had not been treated with aspirin .  SETTING Tx levels in the pericardial fluid , oxygenation , and bleeding were compared between the two groups . PATIENTS Thirty-two patients with coronary artery disease who were undergoing coronary artery bypass grafting . Fourteen of these patients received aspirin until the day of the operation , whereas 18 patients stopped receiving aspirin at least 1 week before undergoing the operation . MAIN RESULTS Mean ( + /- SD ) Tx levels in the pericardial fluid were significantly lower in the aspirin group ( 117 + /- 47 pg/mL ) compared to those in the control group ( 1,306 + /- 2,048 pg/mL ; p = 0.02 ) . The duration of ventilation after the operation was significantly longer in the nonaspirin group ( 9.6 + /- 5.6 h vs 3.8 + /- 1.4 h , respectively ; p = 0.0004 ) . Po(2 ) reached a higher level while patients breathed 100 % O(2 ) in the aspirin group ( 235 + /- 54 mm Hg vs 176 + /- 27 mm Hg , respectively ; p = 0.001 ) . The mean amount of bleeding during the first 24 h after surgery was increased in the aspirin group ( 710 + /- 202 mL ) compared with the nonaspirin group ( 539 + /- 143 mL ; p = 0.01 ) , but these patients did not require more transfusions . CONCLUSIONS The administration of aspirin until the operation may improve oxygenation with only a slight increase in bleeding . This improvement is probably mediated by antiplatelet activity and Tx inhibition by aspirin OBJECTIVE To determine whether coronary graft patency can be predicted by  transit time flow measurement ( TTFM ) . METHODS From May 1 1997 to December 31 1998 , TTFM was prospect ively evaluated in 409 patients undergoing coronary artery bypass grafting ( CABG ) without card 
    Output:
    
In patients undergoing coronary artery surgery , preoperative aspirin reduces perioperative MI , but at a cost of increased bleeding , blood transfusion , and surgical re-exploration