since the introduction of large - bore catheters for acute hemodialysis more than 50 years ago [ 1 , 2 ] , many problems with handling , materials , and contamination of these catheters have arisen . catheterization of the femoral vessels produces more complications than the catheterization of the superior vena cava ( svc ) . cannulation of the svc versus the subclavian vein is difficult to implement and involves a higher complication rate [ 2 , 3 ] . using the infraclavicular catheterization technique , it is often difficult to push the large - bore catheter under the clavicle . because of the anatomical position of the subclavian vein , perforation is more likely with a rigid , large - bore catheter , apart from the danger of causing a pneumothorax or a hemothorax [ 39 ] . despite technical innovations in hemodialysis ( hd ) and apheresis , the problems of providing temporary or permanent vascular access appear to have found no satisfactory solution . therefore , many investigators have inserted large - bore catheters in the superior vena cava rather than in the internal jugular or the subclavian veins [ 39 ] . dialysis catheters are used for vascular access in 65% of incident hemodialysis patients , and in 25% of the prevalent hd populations . complication rates due to infections for venous catheters are reported to be between 34 and 40% and more [ 11 , 12 ] . infections present a particular problem because they can appear at any time , even years after an implantation , and may affect all materials . treatment with systemic antibiotics alone without removal of the catheter fails to definitively eradicate the infection in most patients . catheter - related bacteremia can be managed by either catheter removal with delayed placement of a new catheter or exchange of the infected catheter with a new catheter over a guide - wire and additional systemic antibiotic therapy . the source of catheter - related bacteremia is in most patients a bacterial biofilm , which forms in the catheter lumen . this biofilm , mostly consisting of staphylococcus aureus , can not be destroyed or eliminated by a systemic antibiotic therapy because of antimicrobial resistance . in 1981 , locci et al . demonstrated that bacterial could most of the time colonize artificial , rough surfaces . the combination of tough surfaces and protein deposits should be an ideal situation for the colonization of bacteria . the bacteria could produce and become covered with a slime layer , in which case antibiotic drugs have no influence on the bacteria . the bacteria under the slime layer use the organic substances of the catheter material for their metabolism . the toxins of the bacteria can penetrate the slime layer and enter the patient blood provoking a catheter infection . biofilm is a microbial - derived sessile community characterized by cells that are irreversibly attached to a substratum or to interface to each other , embedded in a matrix of extracellular polymeric substances that have produced . such a biofilm can be the origin of fibrin sheath formations leading to catheter dysfunction due to blood flow reducing and to blood disturbances . the therapy must be to remove the catheter immediately or exchange it over a guide - wire with a new catheter and additional systemic antibiotic therapy . the interaction of blood with a synthetic surface causes coagulation and activation of the complement system . this can lead to the adsorption of various proteins and the formation of a layer of protein on the synthetic surface . thrombocytes , other cells , and bacteria adhere to this layer of protein so that thrombi may form , which can lead to blood flow disturbances and catheter dysfunction . because of these problems , surface modification processes that can reduce the rate of infection or thrombogenicity , without adversely affecting basic catheter design and functionality , are of special interest . the large - bore catheter has been frequently modified over recent years , and all models available are of similar construction with single , double , or triple lumen [ 1825 ] . to influence catheter - related bacteremia , different new developments are available today , like coating of the catheter surface with antibiotic - heparin , cuffs on the outer surface , catheter for tunnelling , installation of an antibiotic - anticoagulant lock into the catheter lumen after the hd , and so forth , [ 13 , 26 , 27 ] . the authors introduced in 1979 the transcutaneous insertion of large - bore catheters through the internal jugular vein , and in 1992 they used for the first time available catheters which were coated on the outer surface with silver . in a retrospective study from 1992 to 2007 , all catheters with surface treatment of silver versus untreated catheters were investigated after removal using a scanning electron microscope . also , bacterial colonization and thrombus accumulation and the cuffs of the catheters after fixation were also investigated . in a preliminary study from 2001 , the authors found a decline of the infection rate with the surface - treated catheter . to examine these results in a 15-year study most of the available single- , double- or triple - lumen catheters have some deficiencies depending on the material . no problem is experienced with polyurethane catheters after the incorporation of contrast media ; however , the latter material may affect catheter durability when using teflon . this problem was overcome by making a thicker catheter wall , but this caused endothelial irritation and early thrombus formation . catheters providing radio contrast are not absolutely necessary , however , because their position can be controlled more simply and gently with an intra - atrial electrocardiogram lead ( ia ecg ) . the three most important criteria of any catheter material are a good tolerance , a low thrombogenicity , and a low infection rate [ 30 , 31 ] . rarely do the material properties perfectly match every requirement in a given application and biomaterials are no exception . for instance , although a candidate orthopedic material may have ideal mechanical properties , it may elicit a deleterious biological response , or a candidate biosensor with good electrical characteristics may corrode readily in the presence of body fluids . therefore , it often becomes necessary to strike a compromise so that a material has acceptable properties in each pertinent area . for example , in a product such as a hemodialysis catheter , which demands both good flexibility and low surface friction , the best candidate may be a slippery , less flexible material rather than a more supple one with unacceptably high friction . a wide spectrum of biomaterial surface properties , including biological , mechanical , chemical , and other properties that directly influence biocompatibility and functionality , can be modified . surface engineering is generally considered when a  good  surface is not good enough , when devices would not function without it , or when product differentiation is desired . the importance of surface - engineered biomaterials has been recognized by major medical device companies , because surface modification processes can reduce the rate of infection , thrombogenicity , and other catheter - related complications without adversely affecting the basic design function of catheters .   although the field is still essentially in its infancy , the range of services currently offered by surface treatment vendors is varied and continually expanding . examples include conventional coating process such as depending and spraying , vacuum - deposition techniques ( e.g. , sputtering ) , and surface modification approaches such as diffusion ( nitriding , carburizing ) , laser and plasma processes , chemical plating , grafting or bonding , and bombardment with energetic particles ( as in plasma immersion or ion implantation ) . of the available techniques , those based on ionised particle bombardment have been particularly successful in biomaterial surface modification , primarily because they combine versatility and low - temperature processing with superior process control , reliability , and reproducibility . the ion - beam - based technology used for the treatment of catheters covered herein is ion - beam - assisted deposition ( ibad ; spi - argent , spire corporation , bedford , ma , usa ) [ 3335 ] . the affected layer in the typical films deposited by the ibad process is in the order of 1  m or less , so vacuum - compatible catheter materials may , therefore , be treated without adversely affecting bulk mechanical properties . this implies that only the outer surface of the catheters can be treated directly ; however , parts with complicated geometries may be manipulated for uniform coverage of all surfaces . silver has been indicated as a good prospect for an infection - resistant coating material for catheters . the problem previously preventing the use of silver on catheters has been the inability to deposit adherent films of silver on flexible polymeric substrates . the ibad process permits the formation of silver coatings at a relatively low temperature with extremely good adhesion that prevents delamination of the film during extended exposure to bodily fluids . the ibad silver - deposited film has a low coefficient of friction , is highly uniform , and has demonstrated excellent adhesion . the authors present the retrospective study from 1992 to 2007 ; the inclusion criteria were patients > 18 years of age who requires a large - bore catheters ( in-/outpatient ) , were free of bacteremia , and provided informed consent . the exclusion criteria were a pregnant or lactating female , a hypersensitivity of silver , and a bacteremia at the time of catheter insertion . an irb approval was in 1992 not necessary . in the study , a total of 159 patients ( age 66.5  13.2 years , females n = 94 ( 59% ) are involved ( table 1 ) ) . large - bore , single lumen catheters were inserted percutaneously in the internal jugular or subclavian veins . the percutaneously catheterisation was necessary in renal failure because of acute kidney injury ( aki ) for hemodialysis due to cardiovascular disease , postoperative aki , and so forth , and in end - stage renal disease ( esrd ) because of clotting fistula , septicemia , abscess and catheter thrombosis , and faults in the catheter material ( n = 138 ( 86.8% ) ) ( table 2 ) . further indications to catheterisation were access problems in patients with familial hypercholesterolemia ( n = 12 ( 7.5% ) ) , different indications for plasmapheresis ( n = 7 ( 4.4% ) ) , and in 2 patients with carcinoma ( n = 2 ( 1.3% ) ) . in 54 patients ( 34% ) , a catheter with a silver coating on the outer surface ( spi - argent , spire , bedford , ma , usa ) was inserted , and 105 patients ( 66% ) received untreated catheters . patients with untreated catheters were younger ( 62.2  16.2 versus 68.8  10.7 , p = 0.003 ) , but there were no differences between the groups regarding gender distribution , diagnosis , or extracorporeal detoxification methods . the catheters were placed by nephrologists after the seldinger technique and/or under fluoroscopic guidance . before percutaneous insertion , each patient skin was disinfected using a consistent method , and a sterile skin smear was taken for microbiologic examination , and then the catheter was inserted . before fixing the catheter with a suture , its position ( particularly the catheter tip ) should be checked with a normal radiological control and/or with an ia ecg . in long - term catheters , catheters were removed either when other vascular access routes became available or when serious infections developed , or if the catheter was not longer necessary . before catheter removal , a skin smear was taken . the catheters were then removed under sterile conditions , and the tip was examined bacteriologically . in the remainder , the catheter was rinsed in a physiological saline solution and fixed in a solution of phosphate buffer containing glutaraldehyde and formaldehyde for histological investigation . statistical analysis was performed using the statistical package for social sciences ( spss 13.0 ) . all continuous data are presented as mean  standard deviation ( sd ) or if the data showed no normal distribution , as median and range . dichotomous data were presented as a number ( n ) or in percent ( % ) . univariate , unadjusted analyses were performed with the independent samples t - test , chi - square test , fisher 's exact test for frequencies at or below 5 , and the wilcoxon 's rank sum test . pearson 's correlation coefficient was calculated and multivariate analysis was used to evaluate the presence of associated variables . the median in situ period untreated and silver - coated catheters were 138.9 ( range , 11,845 ) and 115.0 ( range , 41,348 ) days , respectively , ( p = 0.653 ) . calculating the in situ times after classification for different age groups , it will be overt , that in patients older than 45 years , in situ times were significantly longer ( p < 0.01 ) ( figure 1 ) . comparing the in situ times of untreated catheters after classification for in situ times , there was a tendency towards longer in situ times for the silver - coated catheters ( figure 2 ) . in the median untreated catheters were used for 51 ( range , 1625 ) treatments , silver - coated catheters for 39.0 ( range , 1670 , p = 0.849 ) treatment sessions . performing microbiologic examinations , of the untreated catheters tips , 55% cultured positive for bacteria . of the cultures in patients with surface - treated catheters , although untreated catheters showed a lower infection rate with staphylococcus aureus , in treated catheters the infection rate with staphylococcus epidermidis , pseudomonas , and others such as saprophytes were not significantly lower ( table 3 ) . performing multivariate analysis , there was a strong association between catheters ' in situ period ( r - square = 0.96 ) , the number of treatment sessions (  = 0.97 , p < 0.001 ) , and patients ' age (  = 0.095 , p = 0.002 ) . there was no association between the in situ time and silver - coated / untreated catheters , results of the bacteriological examination , and patients diagnosis or outcome . catheter malfunction or fibrin sheath formation as an outcome of both groups was not investigated . the decrease of the infection rate in surface - treated catheter in the preliminary study from 2001 can not be seen in this presented study from 1992 to 2007 . the untreated catheters showed a higher positive culture for bacteria of 55% versus 52% to surface - treated catheters , but without significance . catheter - related bacteremia and thrombosis are the most dangerous complications of large - bore catheter aside from accidental puncture of an artery . in addition to colonization , biocompatibility of a catheter material is an important contributing factor to a successful clinical outcome , particularly in catheters that remain in situ for several weeks or months . though improved since the use of centrally placed catheters , the incidence of catheter clotting was previously very high . infection rates range from 5 to 30% and the most bacteria found is the staphylococcus aureus . these rates do not depend on the route of vascular access [ 39 , 40 ] . catheter - related staphylococcus aureus bacteremia is one of the main causes of morbidity and a preventable cause of death in hemodialysis . patients on dialysis are at a high risk of staphylococcus aureus bacteremia , and they have a four times higher mortality from central venous catheter - related staphylococcus aureus bacteremia than other patients [ 14 , 41 , 42 ] . as such , new surgical techniques , catheter materials , and therapeutic drugs , and sterile handling during the treatments that influence performance and longevity of catheters are of great interest to the medical community [ 43 , 44 ] . these catheter - related complications are contributing factors to the increasing cost of medical care . they are responsible for patient readmissions and longer hospital stays as well as patients discomfort , morbidity , and occasional mortality . , the costs of the morbidity due to catheter infections will soon exceed $ 1 billion per year . therefore , he demanded to reduce vascular - access - related morbidity and that strategies must be developed not only to prevent and detect appropriately early synthetic vascular access dysfunction , but to better identify the patients in a whom radial arteriovenous fistula is a viable clinical option . table 4 shows representative health care cost savings for hemodialysis catheters , given specific infection rates and potential infection rate reductions achieved by treated catheters . the cost analysis was calculated using the literature and the available costs of different companies , which distribute these catheters . to reduce infection rates and thrombogenicity , coated catheters and cuffs the clinical results of our preliminary investigations showed a significantly reduced infection rate in treated versus untreated catheters , a reduction of more than 75% . with the silver surface treatment , a very smooth metallic surface was obtained , which was responsible for a lower thrombogenicity rate . silver ions are bactericidal , therefore , no bacteria growth is possible on the treated catheter surface . the positive association between the in situ time of the catheters and the patients ' age maybe because of an alteration of the immune system in elderly patients , especially in hemodialysis patients . but in our retrospective study of all silver - coated catheters no significant reduction in infection rate , improvement , or life expectancy of silver - coated versus untreated catheters , which were inserted during 19922007 , was observed . one reason can be that with the ibad technology , only the outer surface is coated with silver . the postulated penetration of silver ions from the outer to the inner surface can not be shown with these results . the only outer - surface - treated catheters with silver have no advantage in point of view of reducing infection rate and improvement of patients versus the untreated catheters . the handling of the catheters before , during , and after the extracorporeal treatments can not prevent the contamination with bacteria , especially the untreated inner side . based on these results , new materials must be developed , which should have better biocompatibility to reduce side effects so that they can be left in situ for a long time , because the part of dialysis in patients with vascular problems is increasing in the last decade , because the age of hd patients is permanently growing up . as the requirement for more and more artificial organs and/or organ replacements increases , especially in elderly patients , there will be a definite need for new materials with better biocompatibility and for suitable technologies to solve these infection , thrombosis , and medical problems to reduce the costs and get a better improvement of patients . this requirement shows perhaps the new developed catheter material , the microdomain - structured surface ( pur - sma - coated catheters , gambro , germany ) . microdomain surfaces are considered the most biocompatible because they mimic the structure of natural biological surfaces . microdomain structures are used to match the multiple requirements for improved catheter surfaces , that is reduced thrombogenicity and improved antimicrobial properties . an sma - modified polyurethane coating consists of hydrophobic and hydrophilic microdomains in range below 50  nm . up to 50 percent of the sma molecule is presented to the surface and creates microdomain structures surfaces . if the domains are below a critical dimension of approximately 100  nmm , theoretical considerations indicate that interaction with proteins , blood cells , or even bacteria will be unstable and therefore , not occur as frequently as on non - microdomain structured surfaces . the new pur - sma coating prevents contact of blood components with barium sulfate , possibly leading to leaching as particles or dissolving in the surrounding media . the advantage of the pur - sma surface treatment is the coating of the inner and the outer surface in contrast to the ion - beam - based surface treatment technologies in which can be treated only the outer surface of the catheters . the preliminary results with these pur - sma - coated catheters showed a good biocompatibility without any blood deposits and a low thrombogenicity and coagulation activity . more new materials must be developed , which should have better biocompatibility to reduce side effects so that they can be left in situ for a long time , because the part of dialysis in patients with vascular problems is increasing in the last decade . as the requirement for more and more artificial organs and/or organ replacements increases , there will be a definite need for new materials with better biocompatibility and for suitable technologies to solve these infection , thrombosis , and medical problems to reduce the costs and get a better improvement of patients . but it appears impossible to create a surface with an absolute  zero  adherence due to thermodynamical reasons and due to the fact that a modified material surface is in vivo rapidly covered by plasma and connective tissue proteins . therefore , other concepts of the prevention of implant - associated infections must involve the impregnation of the devices in the inner and outer surface with antibiotics , antimicrobial substances , and/or metals . another point is to understand the processes leading to the development of catheter - related bacteremia in order to offer effective preventative and therapeutic possibilities . in a retrospective study from 1992 to 2007 , outer - surface - treated catheters with silver versus untreated catheters in 159 patients , who needed a large - bore catheter , were investigated . the results of a preliminary study from 2001 , which showed 75% decline in the infection rate with the surface - treated catheters , can not be confirmed with the presented study . there was no association between the in situ time and silver - coated / uncoated catheters , results of the bacteriological examination , and patients diagnosis or outcome . one reason maybe that in the surface - treated catheters only the outer surface was coated with silver and another reason is the possibility of contamination by the handling during the extracorporeal treatments . therefore , new materials and surface treatment technologies are needed to save health care costs for hemoldiaysis catheters , to reduce infection rates and thrombus formations and help to improve the patients outcome .
background . 
 catheter - related infections , thrombosis , and stenosis are among the most frequent complications associated with catheters , which are inserted in vessels 
 . surface treatment processes of the outer surface , such as ion - beam - assisted deposition , can be used to mitigate such complications . 
 methods . 
 this retrospective study ( 19922007 ) evaluated silver - coated ( 54 patients ) and noncoated ( 105 patients ) implanted large - bore catheters used for extracorporeal detoxification . 
 the catheters were inserted into the internal jugular or subclavian veins . 
 after removal , the catheters were cultured for bacterial colonization using standard microbiologic assays . 
 they also were examined using scanning electron microscope . 
 results . 
 the silver coated catheters showed a tendency towards longer in situ time . 
 the microbiologic examinations of the catheter tips were in both catheter types high positive , but not significant . 
 conclusion . 
 the silver - coated catheters showed no significantly reduction in infection rate by evaluation of all collected data in this retrospective study . 
 there was no association between both catheters in significantly reducing savings in treatment costs and in reducing patient discomfort . 
 other new developed catheter materials such as the microdomain - structured inner and outer surface are considered more biocompatible because they mimic the structure of natural biological surface .