***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: The efficacy of low-dose heparin in preventing fatal postoperative pulmonary embolism has been investigated in a multicentre prospect i ve r and omised trial . 4121 patients over the age of forty years undergoing a variety of elective major surgical procedures were included in the trial ; 2076 of these were in the control group and 2045 patients received heparin .  The two groups were well matched for age , sex , weight , blood-group , and other factors which could predispose to the development of venous thromboembolism . 180 ( 4 - 4 % ) patients died during the postoperative period , 100 in the control and 80 in the heparin group : 72 % of deaths in the control and 66 % in the heparin group had necropsy examination . 16 patients in the control group and 2 in the heparin group were found at necropsy to have died due to acute massive pulmonary embolism ( P smaller than 0 - 005 ) . In addition , emboli found at necropsy in 6 patients in the control group and 3 in the heparin group were considered either contributory to death or an incidental finding since death in these patients was attributed to other causes . Taking all pulmonary emboli together , the findings were again significant ( P smaller than 0 - 005 ) . Of 1292 patients in whom the 125-I-fibrinogen test was performed to detect deep-vein thrombosis ( D.V.T. ) 667 were in the control group and 625 in the heparin group . The frequency of isotopic D.V.T. was reduced from 24 - 6 % in the control group 7 - 7 % in the heparin group ( P smaller 0 - 005 ) . In 30 patients D.V.T. was detected at necropsy ; 24 in the control and 6 in the heparin group ( P smaller 0 - 005 ) . 32 patients in the control group and 11 in the heparin group developed clinical ly diagnosed D.V.T. which was confirmed by venography ( P smaller than 0 - 005 ) . In addition , 24 patients in the control and 8 in the heparin group were treated for clinical ly suspected pulmonary emoblism . The difference in the number of patients requiring treatment for D.V.T. and /or pulmonary embolism in the two groups was again significant ( P smaller than 0 - 005 ) . 9 patients were found at necropsy to have died from haemorrhage ; 5 were in the control and 4 in the heparin group . A careful objective analysis of operative and postoperative bleeding in 1475 patients showed no statistically significant difference in the blood-transfusion requirements or in the fall in the postoperative haemoglobin level either in the individual operative groups or in the group as a whole . However , the difference in the number of patients who developed wound haematoma in the heparin and control groups was significant ( P smaller 0 - 01 ) . The results of the trial indicate that this form of prophylaxis can now be recommended for use on a large scale in " high-risk " patients undergoing major surgery The efficacy of cimetidine in the prevention of  gastrointestinal haemorrhage  in a general intensive care unit was evaluated in 221 patients by a placebo controlled double blind r and omised study . Criteria for bleeding were ( i ) haematemesis or gastric aspirate greater than 50 ml fresh blood , ( ii ) melaena or fresh blood per rectum with an upper source verified by endoscopy if the gastric aspirate was clear , ( iii ) a fall in haemoglobin level greater than 2 g/dl in a 24 hour period associated with either 4 + occult blood in stools , or coffee ground gastric drainage of at least 100 ml . The drug and placebo groups were similar for age , sex , duration of study and risk factors . One hundred and fourteen received cimetidine and 107 placebo . Only 8 % of the patients bled with no significant difference between the two groups ( 6/114 cimetidine , 11/107 placebo ; p = 0.16 ) . There was no correlation between the frequency of bleeding and either the number of risk factors per patient or the duration of intensive care unit stay . Thirteen patients died in each study group , result ing in overall mortality of 12 % . The low incidence of haemorrhage , the lack of statistical benefit from cimetidine and the similar mortality all argue against the routine use of this drug in intensive care unit patients Objective To determine the prevalence of deep vein thrombosis ( DVT ) among patients requiring prolonged mechanical ventilation in the intensive care unit . Design Prospect i ve cohort study . Setting Medical intensive care unit of a university-affiliated urban teaching hospital . Patients Patients requiring mechanical ventilation for > 7 days . Interventions All patients admitted to the medical intensive care unit requiring prolonged mechanical ventilation  underwent duplex ultrasonography of their lower extremities and upper extremities every 7 days . The main outcome identified was the presence of DVT . Secondary outcomes included hospital mortality , hospital and intensive care unit lengths of stay , and the occurrence of pulmonary embolism . Measurements and Main Results A total of 110 patients requiring mechanical ventilation for > 7 days were enrolled . Prophylaxis against DVT was employed in 110 of the patients ( 100 % ) . A total of 26 patients ( 23.6 % ) developed DVT . Patients with DVT were statistically more likely to have underlying malignancy ( 30.8 % vs. 8.3%;p = .004 ) and longer duration s of central venous catheterization ( 26.9 ± 22.2 days vs. 14.5 ± 12.1 days;p = .024 ) compared with patients without DVT . There were no statistically significant differences in hospital mortality or lengths of stay in the hospital and intensive care unit for patients with and without DVT . Patients documented to have DVT by using duplex ultrasonography had a statistically greater frequency of subsequent pulmonary embolism during their hospitalization ( 11.5 % vs. 0.0%;p = .012 ) . Conclusion The occurrence of DVT is common among patients requiring prolonged mechanical ventilation in the intensive care unit setting despite the use of prophylaxis measures . These data suggest that alternative strategies for the prevention of DVT should be evaluated . Additionally , early detection methods should be considered to reduce the potential morbidity associated with untreated DVT in this high-risk population Objective To study the incidence of stress-ulcer related bleeding in ICU patients receiving prolonged ( > 2 days ) mechanical ventilation without any stress ulceration prophylaxis . Design A prospect i ve cohort study in 183 patients . Interventions All patients received clinical treatment including maintenance of adequate tissue perfusion ( with low dose inotropes and vasodilators ) , infection prevention ( by selective decontamination of the digestive tract ) throughout ICU stay and suppression of generalized inflammatory reaction ( by steroids ) . Setting Medical/surgical ICU of a major teaching hospital in Amsterdam ( Onze Lieve Vrouwe Gasthuis ) . Measurements and results 167 patients were evaluated during 2182 treatment days in the ICU and during 1753 days on mechanical ventilation without stress ulceration prophylaxis . The mean total risk score for stress ulcetation related bleeding was 38 ( Tryba score ) . Stress ulceration realted bleeding developed in 1 patient ( 0.6 % ) . Conclusions The incidence of SURB was less then 1 % in this cohort of ICU patients receiving longterm mechanical ventilation  with a high risk for SURB ( mean total risk score 38 ) . All patients received agressive shock resuscitation , infection prevention with selective decontamination of the digestive tract ( SDD ) and suppression of inflammatory response with steroids . Further studies are needed to evaluate the contribution of each of these elements of the integral approach In a multicentre , r and omized , double-blind controlled trial comparing the low-molecular-weight heparin enoxaparin ( 40 mg ) with a st and ard unfractionated heparin ( Ca-heparin , 3 x 5,000 U ) in deep-vein thrombosis prophylaxis in a high-risk group of 959 hospitalized medical patients , enoxaparin was at least as efficacious as st and ard heparin , with fewer adverse events In a prospect i ve , controlled , r and omized study of a prophylaxis for stress bleeding , 100 high-risk patients in an intensive care unit received , on a daily basis , 1 g of sucralfate every four hours , an antacid every two hours , or 2 g of cimetidine intravenously . All patients also received 50 mg of pirenzepine by intravenous infusion each day . Gastric pH was determined every eight hours . Bleeding was defined as macroscopically visible bleeding . The intragastric pH was less than 4 significantly more often in patients treated with sucralfate than in patients treated with the other agents , but stress bleeding occurred only in patients treated with cimetidine ( n = 2 ) or antacids ( n = 2 ) . In the latter two treatment groups , the probability of bleeding correlated with the incidence of pH values below 4 . No side effects of sucralfate therapy  were observed . The results indicate that prophylactic treatment of stress bleeding with pirenzepine and sucralfate is at least as effective as combined treatment with pirenzepine and cimetidine or antacids 166 patients aged 40 - 80 years were included in a controlled , r and omized , double-blind study to determine the efficacy and safety of a single daily injection of a low molecular weight ( LMW ) heparin for prevention of  deep-vein thrombosis  compared to low dose conventional heparin . Patients received 1 x 1.500 aPTT units of a LMW heparin fraction ( plus 2 x placebo injection ) or 3 x 5.000 IU of an unfractionated heparin . During 10 days of treatment , patients underwent repeated clinical investigation , serial impedance plethysmography , and Doppler sonography for detection of thrombosis of the lower limbs . Combined application of these methods revealed evidence of thrombosis in 4.5 % of patients on unfractionated heparin and 3.6 % of patients on LMW heparin .  Subcutaneous hematomas were significantly smaller in diameter upon treatment with LMW heparin ( p less than 0.001 ) . Antithrombin III levels were significantly higher at the end of the observation period in the LMW heparin group ( p less than 0.005 ) . Thrombocyte count , transaminases , creatinine , and haemoglobin did not change in either group . The results indicate that LMW heparin administered by a single s.c . dose daily may be as effective as low dose heparin in prevention of deep venous thrombosis in medical in patients OBJECTIVES To determine the rate of lower extremity deep vein thrombosis after the use of femoral catheters in intensive care unit ( ICU ) comatose or se date d adults . Results were then compared with results of patients undergoing superior vena cava catheterization .  DESIGN Prospect i ve , r and omized , controlled , unblinded study . SETTING A mixed medical/surgical ICU in a university hospital . PATIENTS Sixty-one comatose or se date d patients admitted to the ICU who underwent central venous catheterization .  INTERVENTIONS Patients were monitored for signs of thrombotic complications . On catheter removal , a lower-extremity bilateral phlebographic examination  was performed in each patient . MEASUREMENTS AND MAIN RESULTS After r and omization , 31 patients underwent femoral vein catheterization and 30 patients underwent superior vena cava catheterization , either by axillary ( 21 patients ) or internal jugular vein ( 10 patients ) cannulation .  Single lumen polyurethane catheters were inserted for a mean duration of 7.1 + /- 4.6 ( SD ) days in the femoral vein group and 9.9 + /- 5.5 days in the superior vena cava group ( p = NS ) . No patient had clinical signs of leg venous thrombosis or pulmonary embolism during the study period . In each patient , lower extremity bilateral phlebography was performed at the time of catheter removal . Leg phlebographies were normal in 18 ( 60 % ) patients in the femoral vein group and 26 ( 84 % ) patients in the superior vena cava group . Fibrin sleeves which developed around the femoral catheters were seen in seven ( 23.3 % ) patients in the femoral vein group and in no patients in the superior vena cava cannulation group . Three patients had femoral vein thrombosis , two ( 6.6 % ) patients in the femoral vein group ( two nonobstructive thromboses , adherent to the common femoral vein wall ) and one ( 3.0 % ) patient in the superior vena cava group ( nonobstructive thrombosis which developed in the superficial femoral vein ) ( p = NS ) . Lower deep extremities thrombosis developed in five ( 16.7 % ) patients in the femoral vein group and in five ( 16 % ) patients in the superior vena cava group ( p = NS ) . CONCLUSIONS Femoral vein catheterization with a polyurethane catheter is associated with a lower rate of extremity deep vein thrombosis which is similar to the rate observed after superior vena cannulation in comatose or se date d patients .  Femoral vein thrombosis was observed at a rate of 6.6 % after femoral vein cannulation and a rate of 3 % after superior v 
    Output:
    
Histamine-2 receptor antagonists are more effective than sucralfate in decreasing bleeding risk and transfusion requirements .
Proton pump inhibitors have not been assessed in a direct comparison with histamine-2 receptor antagonists but do demonstrate equivalency and ability to increase gastric