***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: OBJECTIVE The construction of an autogenous radial-cephalic direct wrist arteriovenous fistula ( RCAVF ) is the primary and best option for vascular access for hemodialysis . However , 10%-24 % of RCAVFs thrombose directly after operation or do not function adequately due to failure of maturation . In case of poor arterial and /or poor venous vessels for anastomosis , the outcome of RCAVFs may be worse and an alternative vascular access is probably indicated . A prosthetic graft implant may be a second best option . Therefore , a r and omized multicenter study comparing RCAVF with prosthetic ( polytetrafluoroethylene [ PTFE ] ) graft implantation in patients with poor vessels was performed . METHODS A total of 383 consecutive new patients needing primary vascular access were screened for enrollment in a prospect i ve r and omized study . According to defined vessel criteria from the preoperative duplex scanning , 140 patients were allocated to primary placement of an RCAVF and 61 patients to primary prosthetic graft implantation . The remaining 182 patients were r and omized to receive either an RCAVF ( n = 92 ) or prosthetic graft implant ( n = 90 ) . Patency rate was defined as the percentage of AVFs that functioned well after implantation . RESULTS Primary and assisted primary 1-year patencies were 33 % + /- 5.3 % vs 44 % + /- 6.2 % ( P = .03 ) and 48 % + /- 5.5 % vs 63 % + /- 5.9 % ( P = .035 ) for the RCAVF and prosthetic AVF , respectively . Secondary patencies were 52 % + /- 5.5 % vs 79 % + /- 5.1 % ( P = .0001 ) for the RCAVF and prosthetic AVF , respectively . Patients with RCAVFs developed a total of 102 ( 1.19/patient-year [ py ] ) vs 122 ( 1.45/py ; P = .739 ) complications in the prosthetic AVFs . A total of 43 ( 0.50/py ) interventions in the RCAVF group and 79 ( 0.94/py ) in the prosthetic graft group were needed for access salvage ( P = .077 ) . CONCLUSIONS Although there were more interventions needed for access salvage in the patients with prosthetic graft implants , we may conclude that patients with poor forearm vessels do benefit from implantation of a prosthetic graft for vascular access OBJECTIVE To compare the patency of autologous and graft-bridging ( prosthetic )  arteriovenous ( AV ) fistulas in patients 70 years of age or more . DESIGN Non-r and omised comparative study . SETTING University hospital , Greece . PATIENTS 114 patients aged 70 years or more ( mean 78 ) who required 135 consecutive angioaccess procedures during the 8-year period January 1990-December 1997 . INTERVENTIONS 68 autologous and 67 prosthetic procedures , 64 of the prosthetic procedures being proximal brachioaxillary AV arm grafts . MAIN OUTCOME MEASURES Primary and secondary cumulative patency rates and cumulative survival . RESULTS Life table analysis showed that the 3-year secondary patency ( medium term patency ) was significantly superior in the prosthetic group ( 58 % compared with 44 % , p = 0.04 ) . Cumulative survival at 3-years was 21 % . CONCLUSIONS A proximal brachioaxillary prosthetic AV graft is a good alternative as initial primary access in elderly patients who are not suitable for an autologous proximal AV fistula . At this age long term patency and conservation of proximal access sites are of minimum importance because of their limited life expectancy BACKGROUND Vascular access is a necessity for patients with end-stage renal disease who need chronic intermittent hemodialysis . According to Kidney Disease Outcomes Quality Initiative ( KDOQI ) guidelines , radial-cephalic ( RC ) and brachial-cephalic ( BC ) arteriovenous fistulas ( AVF ) are the first and second choice for vascular access , respectively . If these options are not possible , an autogenous brachial-basilic fistula in the upper arm ( BBAVF ) or a prosthetic brachial-antecubital forearm loop ( PTFE loop ) may be considered . Until now , it was not clear which access type was preferable . We have performed a r and omized study comparing BBAVF and prosthetic implantation in patients without the possibility for RCAVF or BCAVF . METHODS Patients with failed primary / secondary access or inadequate arterial and /or venous vessels were r and omized for either BBAVF or PTFE loop creation . The numbers of complications and interventions were recorded . Kaplan-Meier method was used to calculate primary , assisted- primary and secondary patency rates . The patency rates were compared with the log-rank test . Complication and intervention rates were compared with the Mann-Whitney test . RESULTS A total of 105 patients were r and omized for a BBAVF or PTFE loop ( 52 vs 53 , respectively ) . Primary and assisted- primary 1-year patency rates were significantly higher in the BBAVF group : 46 % + /- 7.4 % vs 22 % + /- 6.1 % ( P = .005 ) and 87 % + /- 5.0 % vs 71 % + /- 6.7 % ( P = .045 ) for the BBAVF and PTFE group , respectively . Secondary patencies were comparable for both groups ; 89 % + /- 4.6 % vs 85 % + /- 5.2 % for the BBAVF and PTFE group , respectively . The incidence rate of complications was 1.6 per patient-year in the BBAVF group vs 2.7 per patient-year in the PTFE group . Patients in the BBAVF group needed a total of 1.7 interventions per patient-year vs 2.7 per patient-year for the PTFE group . CONCLUSION These data show a significantly better primary and assisted- primary patency in the BBAVF group compared with the PTFE group . Furthermore , in the BBAVF group , fewer interventions were needed . Therefore , we conclude that BBAVF is the preferred choice for vascular access if RCAVF or BCAVF creation is impossible , or when these types of access have already failed The increased incidence of vascular access thrombosis ( VAT ) associated with recombinant human erythropoietin ( r-HuEPO ) therapy is multifactorial and controversial . Sixty-three hemodialysis patients who received > or = 12 weeks of r-HuEPO therapy  were prospect ively followed for the incidence of VAT . Those who experienced VAT ( Group 1 ) were compared with those who did not ( Group 2 ) . The patients initially received r-HuEPO 50 U/kg intravenously three times a week . The dose was adjusted for a target hematocrit ( t-Hct ) of 30 - 33 % . Twenty-five of the 63 patients ( 40 % ) experienced VAT ( Group 1 ) . These patients were older ( mean , 54.0 + /- 14.0 years versus 47.3 + /- 15.0 years , p = 0.08 ) . There was no difference between Groups 1 and 2 with respect to the baseline Hct level ( 21.5 + /- 2.9 % versus 21.4 + /- 4.3 % ) , the number of patients who achieved t-Hct ( 20 versus 28 ) , and the mean time to reach t-Hct ( 18.6 + /- 15.1 weeks versus 16.9 + /- 16.2 weeks ) . However , 20 of 25 Group 1 patients ( 80 % ) were diabetic compared with only 18 of 38 Group 2 patients ( 47 % , p = 0.0169 , by Fisher 's exact test ) . In addition , the types of vascular access differed markedly between the two groups : arteriovenous ( AV ) grafts/AV fistulae/Permcaths , Group 1 : 21/3/1 versus Group 2 : 15/21/2 , p = 0.0018 . It was concluded that the occurrence of VAT in r-HuEPO treated patients was not related to the patient 's hematologic response to the drug , but rather , it depended upon the integrity of the patient 's vasculature and the type of vascular access used The native arteriovenous fistula ( AVF ) is the preferred vascular access because of its longevity and its lower rates of infection and intervention . Recent studies suggest that the AVF may offer a survival advantage . Because these data were derived from observational studies , they are prone to potential bias . The use of propensity scores offers an additional method to reduce bias result ing from nonr and omized treatment assignment . Adult ( age 18 yr or more ) patients who commenced hemodialysis in Australia and New Zeal and on April 1 , 1999 , until March 31 , 2002 , were studied by using the Australian and New Zeal and Dialysis and Transplant Association ( ANZ DATA ) Registry . Cox regression was used to determine the effect of access type on total mortality . Propensity scores were calculated and used both as a controlling variable in the multivariable model and to construct matched cohorts . The catheter analysis was stratified by dialysis duration at entry to ANZ DATA to satisfy the proportional-hazard assumption . There were 612 deaths in 3749 patients ( median follow-up , 1.07 yr ) . After adjustment for confounding factors and propensity scores , catheter use was predictive of mortality . Patients with arteriovenous grafts ( AVG ) also had a significantly increased risk of death . Effect estimates were also consistent in the smaller propensity score-matched cohorts . Both AVG and catheter use in incident hemodialysis patients are associated with significant excess of total mortality . Reducing catheter use and increasing the proportion of patients commencing hemodialysis with a mature AVF remain important clinical objectives BACKGROUND H and ischemia result ing from arterial steal is a serious complication in patients undergoing hemodialysis access , but specific risk factors for steal remain in dispute . The purpose of this study was to determine whether plethysmographically derived finger pressures ( FPs ) or digital-brachial indices ( DBIs ) are predictive of symptomatic arterial steal . METHODS We prospect ively studied 72 patients ( 37 men , 35 women ; mean age , 57 + /- 10 years ) who were undergoing brachial artery-based hemodialysis access .  All patients had complete pre- and postoperative  h and examinations and FP determinations . Surgeons were blinded to preoperative FP results . RESULTS Prosthetic graft was used in 60 patients ( 6-mm polytetrafluoroethylene [ PTFE ] in 50 , tapered PTFE in 10 ) , and brachial-based arteriovenous fistulas were created in 12 . Fourteen ( 19 % ) patients developed arterial steal symptoms . The mean preoperative FP was significantly lower in steal patients than in those without steal ( 131 + /- 27 vs 151 + /- 31 mm Hg , P < .03 ) . Nine ( 64 % ) of the patients with steal had DBIs < 1.0 , compared to 18 ( 31 % ) of the patients without steal ( P = .02 ) . However , there was no absolute FP or DBI threshold below which steal was inevitable . The occurrence of steal was attributed to proximal arterial stenoses in seven , to distal arterial disease in five , and was unknown in two . When comparing the 14 patients who developed steal to the 58 who did not , we noted that a higher proportion of steal patients had coronary artery disease ( 57 % vs 17 % , P = .005 ) . Steal was more likely to develop in patients with arteriovenous fistulas than in patients with prosthetic grafts ( 43 % vs 14 % , P = .009 ) . There were no significant differences in demographic factors , atherosclerotic risks ( diabetes , smoking , hypertension , dyslipidemia ) , prevalence of peripheral vascular disease , cerebrovascular disease , shunt location , tapered vs straight graft , or number of prior grafts placed . CONCLUSIONS These data indicate that preoperative FPs are lower in patients who develop steal syndrome  after hemodialysis access . Patients with preoperative DBIs < 1.0 are more likely to develop steal , but there is no DBI threshold below which steal is inevitable . Steal is more likely in patients undergoing brachial-based arteriovenous fistulas than in those receiving prosthetic grafts OBJECTIVES To compare patency and complication rates of  polytetrafluoroethylene ( PTFE ) grafts  and denatured homologous vein ( DHV ) grafts for long-term haemodialysis . DESIGN A prospect i ve r and omised multicentre trial . MATERIAL S One hundred and thirty-one patients were enrolled between September 1994 and April 1997 . Sixty-three DHV grafts and 68 PTFE grafts were implanted in 60 meals and 71 females . Complications and interventions were monitored . Patency rates , complication rates , and intervention rates of PTFE and DHV were compared . 
    Output:
    
Low- quality evidence from inconsistent studies with limited protection against bias shows that autogenous access for chronic hemodialysis is superior to prosthetic access