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whichallowforthemaximumnumberoflumenswhilemaintainingaminimumouterdiameter.

Carbothaneisapolyurethane/polycarbonatecopolymerthataffordsstrengthforlongevityandsoftnessfor exibilityandpatientcomfort.Withslightlygreaterstrengththanpoly-urethane,itcanaffordtohavethinnerwalls.Unlikepolyure-thane,copolymersarealsoresistanttoiodine,peroxide,andalcohols.Inthefuture,themajorityofchroniccathetersareexpectedtobeconstructedfromcopolymermaterials.34

Invitroandinvivocomparisonsbetweensiliconeandpolyurethaneascathetermaterialsremaininconclusive.An-imalmodelsappeartoattributeanincreasedinfectionriskandthromogenicitytosiliconecathetersoverpolyurethanecatheters.36,37Itmightbethatsiliconecathetershavearoughertopographyandaremorepronetoconstructionfail-uresbecauseofthemoredif cultmanufacturingprocess.38However,inastudycomparingsiliconeandpolyurethaneCVCsinsertedatthecubitalfossa,neithermaterialwasfoundtobesuperiorinthrombogenecity,plateletadhesion,orcath-eterocclusionrate.39Inastudyofurethralcathetersurfaceproperties,thereisevensomeevidencethatsilicone-basedmaterialsexhibitagreatereaseofremovalthanpolyurethane-basedmaterials,duetogreatersurfacelubricity.40Ionimplan-tationofsiliconerubberhasbeeninstrumentalinimprovingsilicone’shydrophilicityandlendingitresistancetobiomaterialdeposits.Additionally,polyurethanereactsstronglytoalcohol,andtheonlyantibioticointmentthatcansafelybeusedattheexitsiteisNeosporin(P zer,NewLondon,Connecticut).Sili-cone,ontheotherhand,iscompatiblewithmostointments.Althoughcathetermaterialsareselectedtobebiocompat-ibleandhemocompatible,complicationsduetothrombosisandinfectionarestillinevitable.Todate,centralaccessforhemodialysisisstillinferiortoperipheralaccessviaarterio-venous stulaorgraft.

CatheterCoatings

Theuseofantithrombogenicandantimicrobialsurfacetech-nologiesonthecathetersisonewayofreducingthelikeli-hoodofcomplicationsduetothrombosisormicrobialcolo-nization.Inacutecatheterscoatedwithantibiotics,silver,orheparin,thenumberofinfectionscanbereducedsubstan-tially.Heparin-coatedcatheters,inparticular,mayconfertheadditionalbene tofcosteffectiveness.41

Heparin-coatedcatheterspresentawaytodecreaseinfectionratewithouttherisksofsystemicantibioticexposureorbacterialresistance.Heparinexhibitsanticoagulantactivityviainterac-tionwiththeplasmaproteinantithrombinaswellassomeelec-trostaticrepulsionofchargedplatelets.Therefore,itcanreducebacterialtrappingwithin brinclotsandsheaths.15Hydropho-bicandelectrostaticinteractionsalsodecreasedirectbacterialadhesionontocatheterpolymer.Heparinimmobilizedonaplasticsurfacehasbeenreportedtodiminish bronectindepo-sitionandtodecreasebacterialadherenceinvitro.15,42

Severalstudieshavedemonstratedthesafetyandef cacyofusingheparin-bondedcathetersinvivo.Inblinded,pro-spectivestudiesofcriticallyillchildrenrequiringfemoralorcentralvenouscatheterization,twogroupsofresearchershavefoundthatheparin-bondedcathetersareassociatedwithsigni cantlyfewerthromboticcomplicationsandare-ducedincidenceofinfection.43,44Themajorprospectiveclin-

M.G.TalandN.Ni

icalstudyofheparin-bondedcentralvenouscathetersisa1996studybyAppelgrenandcoworkers.15Invitro,coagu-lase-negativeStaphylococciadheredlesstoheparinizedcath-etersthantocontrolcatheters.Theclinicalstudy,whilesmall(32patients),showedthatheparinizedcathetersareassoci-atedwithasigni cantdecreaseincatheter-associatedbacte-remia(26versus0%,P 0.047)andbacterialcolonization(74versus31%,P 0.03).

CovidienofferstheTalPalindromeEmeraldhemodialysiscatheter,whichincorporatesanonelutingheparincoatingtechnologydevelopedbyBioInteractionsLtd.Throughinvitroandinvivotesting,thiscoatinghasbeenshowntoreduceplateletadhesionandthrombusaccumulationonthecathetersurface.Thecoatingdesignadoptsamultifacetedapproachtohemocompatability,bycontainingfunctionalgroupsthathavedemonstratedperformanceinhydrophilic-ity,minimizingplateletadhesion,nonthrombogenicity,andantithrombogenicity.45

SpireBiomedicalInc.offersaheparin-coatedhemodialysiscatheter,marketedastheDecathlonGold,whichincludestheCarmedaBioActiveSurface(CBAS)coating.TheCBAScoatingtechnologyhasalsobeenshowntoreduceplateletadhesionandthrombusaccumulationonthecathetersurfacethroughinvitroandinvivotesting.Inaddressingoneofthekeyproblemsrelatedtosystemicanticoagulationwithhepa-rin,theCBAS“endpoint”attachmentmethodprovidesasta-bleheparin–biomaterialbondthatallowsforlocallyex-pressedheparinactivityatthecathetersurface.46

Theuseofothercoatingmaterialssuchassilverandanti-bioticshasalsobeenpromising.Whileresultshavebeensigni cantforacuteuse,studiesofchronichemodialysiscathetershaveyieldedinconclusiveresults.Forsilver-coatedcatheters,Trerotolaandcoworkers47showednostatisticallysigni cantdifferenceininfectionratebetweenthe47pa-tientsinthetreatmentgroupversusthe44patientsinthecontrolgroup.Twoofthesilver-coatedcatheterswerealsoprematurelyremovedduetosilverallergy.47However,datafromamorerecentlarge-scaleprospectivestudyrevealthatsilvercoatingcanhaveanantimicrobialbene t:inlong-termcoatedcatheters,bacterialcolonizationwasobservedon11%ofcathetertipsversus44%foruncoatedcatheters.48Thekeydif cultywithcoatingchronichemodialysiscathetersisthatthebondedsubstancecandisappearovertime,renderingthemineffectiveoverlongperiods.49

CovidienalsoofferstheTalPalindromeRuby,whichin-corporatesanantimicrobialsilverionsleevebondedbetweenthehubandthecuff.Thissleevedeliverssilverionstothesurfaceofthecathetertoreducemicrobialcolonizationonthecathetersurfacewithinthetunneltrack.InvitrotestingwithclinicalisolatesofStaphylococcusaureus,Coagulase-neg-ativeStaphylococcus,Candidaalbicans,andEscherichiacolihasshowna99.2-99.999%(2.1-5.5log10)reductioninmicro-bialcolonization.45

Covidienisalsoofferingachronicdialysiscatheterthatprovidesbothantithrombogenicandantimicrobialtechnol-ogiesononecatheter,theTalPalindromeSapphire.Thecath-etercombinestheheparin-coatingtechnologywithananti-microbialsilverionsubcutaneoussleeve.50

TheBardHemosplitandHemostarcathetersincludetheBioBloccoating,whichisanelutingsilversulfadiazinetech-nologyintendedtoreducebacterialadhesiononthecatheter