***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: Central haemodynamics and blood gases were measured in 26 patients undergoing elective aortic surgery for atherosclerotic or aneurysmal disease . Recordings were made at seven defined time points , starting before anaesthesia and ending 30 min after declamping of the aorta . The patients were r and omly divided into two groups , one receiving heparin at an early stage and the other at a late stage of the operative procedure . A declamping shock phenomenon could be prevented by thorough blood and fluid replacement . After removal of the aortic clamp the cardiac output increased , except in a few patients who were considered preoperatively to be poor risks . A significant decrease in arterial oxygen tension and increase in pulmonary artery and pulmonary capillary wedge pressures occurred in patients receiving heparin at a later stage . The effect of heparin points to possible intravascular coagulation and pulmonary microembolism during the operation A series of 400 consecutive patients subjected to reconstructive arterial surgery  were r and omly allocated into four equal groups in order to study the effect of dipyridamole and acetylsalicylic acid ( ASA ) in the prevention of deep venous thrombosis and pulmonary embolism . There were 11 drop-outs . In the dipyridamole-ASA group there were no thrombotic complications while in the control group without antithrombotic therapy five cases of deep venous thrombosis and two cases of fatal pulmonary embolism were encountered ( p < 0.05 ) . In the groups receiving either dipyridamole or ASA alone two and four cases of deep venous thrombosis , respectively , were found . It is concluded that treatment with dipyridamole and ASA combined is useful in preventing postoperative thrombotic complication after peripheral vascular reconstructive surgery Forty-four patients undergoing abdominal aortic surgery and twenty-eight patients undergoing carotid surgery  were r and omly treated with different anticoagulant regimens . During surgery , an unfractionated heparin ( UFH ) intravenous bolus of 50 IU/kg was compared with a low molecular weight heparin ( LMWH ) bolus of either 120 IU/kg , 80 IU/kg , 40 IU/kg or 20 IU/kg . Six hours after surgery and for 48 hours , an UFH infusion was compared with an LMWH infusion of either 10,000 IU/day or 6,000 IU/day and then , a single LMWH subcutaneous injection of 3,075 IU was administered . Heparin activity was measured by factor Xa inhibitor and by prolongation of APTT which were studied 15 , 30 and 60 minutes after cross-clamping , at the end of surgery and six hours later , and on days 1 , 2 , 3 and 6 . After a descriptive analysis of clinical and pharmacokinetic profiles of each regimen , optimal LMWH treatment is proposed In a r and omised double-blind controlled trial 24 patients undergoing elective aortic bifurcation graft surgery received subcutaneous calcium heparin ( 2,500 u pre-operatively then 5,000 u 12-hourly for 7 days ) and 25 control patients received saline injections . All patients received a routine dose of intravenous sodium heparin intra-operatively . The trial was terminated because of excess bleeding complications in patients receiving subcutaneous heparin ( 8 vs. 1 , p less than 0.05 ) . Deep vein thrombosis occurred in 6 control patients and 2 patients on heparin ( p less than 0.05 ) . In this group of patients undergoing major vascular surgery the risk of bleeding due to heparin outweighed the potential benefit of thrombotic prophylaxis Heparin anticoagulation during cardiovascular surgical procedures remains poorly investigated and understood . The objective of this investigation was to assess the effectiveness of three methods of heparin administration . Heparin sulfate ( 75 IU/kg ) administered to patients undergoing aortoiliac surgery was r and omised to one of three methods : Group I ( n = 9 ) heparin was injected into a central venous line 5 minutes before infrarenal aortic clamping ; Group II ( n = 9 ) heparin was injected into the distal aneurysm immediately after infrarenal aortic clamping ; and Group III ( n = 8) heparin was injected into a central venous line immediately after infrarenal aortic clamping . Blood sample s were analysed for anticoagulant activity from both the upper and lower extremities at 5 , 15 , 30 , 60 , and 120 minutes after heparin administration . Anticoagulation , as measured by aPTT , antifactor Xa levels , and ACT , was achieved in all three groups by 5 minutes , but initially with lower heparin activity ( measured as antifactor Xa ) in the upper extremity ( Group II ) and lower extremity ( Group III ) , respectively . These differences were also evident in ACT and aPTT determinations .  Intravenous heparin administration prior to aortic cross-clamping achieves excellent anticoagulation ( anti-factor Xa approximately 1 U/ml ) in both upper and lower extremities after 5 minutes . With regional administration , rapid heparin redistribution occurs , but it takes longer to achieve the same level of anticoagulation distant from the site of administration . Nevertheless , from a practical perspective the method of administration does not appear to have a great influence on the eventual achievement of adequate anticoagulation External pneumatic compression ( EPC ) devices prevent lower extremity deep venous thrombosis ( DVT ) by reducing stasis . There is a widely held belief that they also enhance endogenous fibrinolysis ; however , recent studies of tissue plasminogen activator ( the primary activator of fibrinolysis ) and plasminogen activator inhibitor-1 ( the primary inhibitor of fibrinolysis ) failed to confirm this . The hypothesis of this study was that EPC devices increase the level of urokinase plasminogen activator ( uPA ) , a second activator of fibrinolysis . This was a prospect i ve trial in which 44 subjects who underwent major abdominal surgery were r and omized to receive unfractionated heparin injections , thigh-length sequential EPC devices  , or both for DVT prophylaxis . Prophylaxis was begun immediately before surgical incision and continued until postoperative day 5 or discharge . Venous blood sample s were collected from an antecubital vein for measurement of systemic uPA levels and from the common femoral vein for measurement of regional uPA levels . Sample s were collected the day before surgery , after induction of anesthesia but before surgical incision , and on postoperative days 1 , 3 , and 5 . uPA levels ( ng/mL ) were measured with an enzyme-linked immunoassay . Baseline uPA levels ( 0.41 to 0.56 ng/mL ; P > .05 , analysis of variance with repeated measures ) were similar among the three groups . uPA levels did not change after surgery in systemic or regional blood sample s in any group . There were no significant differences in systemic or regional uPA levels in the groups treated with EPC devices relative to those treated with heparin at any time point ( P > .05 , analysis of variance with repeated measures ) . Enhancement of fibrinolysis with EPC devices remains unproven ; the findings reported here suggest that effective DVT prophylaxis can only be assured when the devices are used in a manner that reduces venous stasis The risk of Deep Venous Thrombosis ( DVT ) in the immediate postoperative period varies from 0.8 to 96 % of cases depending on major or minor operations and on age of patients . We have employed 8,000 I.U. AXa/daily of LMW-Heparin injected subcutaneously from one day preoperatively and prolonged for 8 days after surgical procedures in 40 patients operated upon by an aorto-femoral bypass in 25 cases , a femoro-popliteal below the knee in 8 and an extra-anatomical bypass in 7 . The onset of DVP in the lower limbs was investigated by clinical examination , venous Doppler pressure evaluation , waveform analysis and echotomography and the 125I-Fibrinogen uptake test . There was no intraoperative increased bleeding and the preclotting of the prosthetic grafts was inaffected . A DVT was detected during the second postoperative day , by means of the 125I-Fibrinogen test in the calf of only one patient ( 1/40 - 2.5 % ) , su bmi tted to an aorto-bifemoral bypass , in whom the clinical pattern and ultrasound investigations were negative . The single daily subcutaneous administration has never caused side effects in the site of injection and it seems a real improvement in the heparin treatment . These results emphasize the advantage of the use of LMW-Heparins in patients su bmi tted to arterial surgical reconstructions of the lower limbs for the prevention of the DVT The incidence of  postoperative deep vein thrombosis ( PDVT ) after aortic surgery and lower limb revascularisation has not been assessed by a large prospect i ve study . In a prospect i ve r and omised trial the effect of a low-molecular-weight heparin fragment , Enoxaparin ( ENX ) 4200 anti factor Xa IU once daily was compared to that of unfractionated heparin ( UFH ) 7500 IU twice daily . Two hundred and thirty-three consecutive patients were classified into three groups , aortic or aortoiliac and aneurysmectomy ( n = 75 ) , aorto-femoral bypass for atherosclerotic disease ( n = 71 ) , and femoropopliteal or femorodistal bypass ( n = 87 ) . Patients were analysed for development of deep vein thrombosis by Duplex scanning and , if positive , by venography between the seventh and tenth postoperative day . PDVT was present in 10 patients in the ENX group and in four patients in the UFH group ( 8.2 and 3.6 % respectively , NS ) . The incidence of PDVT was 8 % after aortic or aortoiliac aneurysmectomy , 7 % after aortofemoral revascularisation , and 3.4 % after femoropopliteal or femorodistal bypass . The overall incidence of PDVT after aortic surgery was 7.5 % ( 95 % CI 5.4 - 9.7 ) . There was no pulmonary embolism . Intra-operative blood loss and postoperative bleeding events did not differ significantly between the ENX and UFH groups . After 1 month follow-up , no clinical event or death could be related to PDVT or pulmonary embolism . In conclusion , in vascular surgery ENX is as safe and effective in the prevention of PDVT as is UFH OBJECTIVES The primary aim of this prospect i ve multi-centre study involving patients undergoing elective abdominal aortic aneurysm ( AAA ) surgery was to investigate the relationship between intraoperative intravenous heparinisation , blood loss during surgery and thrombotic complications . METHODS Two hundred and eighty-four patients were r and omised to receive intravenous heparin ( n = 145 ) or no heparin ( n = 139 ) . Groups were evenly matched for age , sex , weight , aneurysm size , haemoglobin concentration , platelet counts and distal occlusive disease measured by ankle/brachial systolic pressure . RESULTS There were no statistically significant differences in blood loss ( median 1400 ml vs. 1500 ml ; z = 0.02 , p = 0.98 , 95 % C.I. = -200 to 200 ) , blood transfused ( 4.0 units vs. 4.0 units ; z = 1.09 , p = 0.28 , 95 % C.I. = -1 to 0 ) or distal thrombosis between the two groups . However , analysis of the clinical outcome revealed that 5.7 % of the non-heparin group but only 1.4 % of the heparinised patients suffered a fatal perioperative myocardial infa rct ion ( MI ) ; p < 0.05 . All MI , including non fatal events , affected 8.5 % and 2 % respectively ( p = 0.02 ) . CONCLUSIONS Heparin does not increase blood loss or the need for blood transfusion during surgery . Heparin is not necessary to prevent distal thrombosis when the aorta is cross clamped . The results of the study are consistent with the known mechanisms leading to intraoperative MI and strategies for its prevention . Intravenous heparin , given before aortic cross clamping , is an important prophylaxic against perioperative MI in relation to AAA surgery Elective surgery of abdominal aortic aneurysm ( AAA ) sometimes leads to excessive bleeding and disseminated intravascular coagulation ( DIC ) , even in patients with normal preoperative coagulation parameters . Coagulation screen , performed routinely before surgery is of limited value in the assessment of compensated activation of the haemostatic system . In this study , we used a number of additional tests ( D-dimer , prothrombin fragment 1 + 2 , antithrombin , and activation of fibrinolysis in the platelet poor plasma ) for the diagnosis of compensated activation of the haemostatic system in AAA- patients .  D-dimer and marker of thrombin generation ( prothrombin fragment 1 + 2 ) positively correlated with each other ( r = 0.768 , P < 0.001 ) . Out of  
    Output:
    
There were no data to indicate that post operative anticoagulation , with or without the use of mechanical devices , can safely reduce the incidence of DVT after aortic surgery .
Neither study reported a significant effect of anticoagulants on the incidence of PE or related mortality .
The incidence of minor bleeding events was also slightly higher with anticoagulants .
AUTHORS ' CONCLUSIONS There is not enough evidence to make a definitive conclusion about the use of anticoagulant drugs ( with or without mechanical devices ) for DVT prophylaxis in patients undergoing abdominal aortic surgery