Hemodialysis Vascular Access Dysfunction

IntroductionA successful functioning vascular access is the "lifeline" for a hemodialysis patient.Hemodialysis vascular access dysfunction is a major cause of morbidity and mortality in hemodialysis patients [1][2][3] .Improving vascular access outcomes remains an ongoing challenge for nephrologists, vascular access surgeons, and interventionists.In arteriovenous fistulas (AVF) and grafts (AVG), the most common cause of this vascular access dysfunction is venous stenosis as a result of neointimal hyperplasia within the peri-anastomotic region (AVF) or at the graft-vein anastomosis (AVG) 4,5 .There have been few effective treatments to-date for venous neointimal hyperplasia in part because of the poor understanding of the pathogenesis of venous neointimal hyperplasia.Central venous catheters (CVC) are prone to frequent thrombosis and infection and the treatment of catheter-related bacteremia (CRB) remains on ongoing debate [6][7][8] .Therefore, this review will: (1) describe the pathology and pathophysiology of hemodialysis access stenosis in AVFs and AVGs, (2) discuss the pathogenesis of CRB and catheter thrombosis (3) discuss current and future novel therapies for treating venous neointimal hyperplasia, (4) discuss current strategies to treat CRB and catheter thrombosis, and (5) suggest future research areas in the field of hemodialysis vascular access dysfunction. Types of hemodialysis accessSuccessful hemodialysis treatment requires access to the bloodstream to deliver a high enough blood flow to achieve an adequate dialysis dose.There are three primary types of hemodialysis vascular access to achieve this goal: (1) arteriovenous fistula, (2) arteriovenous graft, and (3) tunneled central venous catheter.Each type of access has unique advantages and individual problems. Arteriovenous fistulaAVFs are the preferred vascular access for hemodialysis patients, because once mature and functional, they require fewer interventions to maintain patency and develop fewer infections compared to AVGs 9-13 .However, AVFs have higher rates of nonmaturation and longer maturation times compared to AVGs, which may lead to prolonged periods of CVC dialysis 9,14,15 .Recent reports from the United States have shown that up to 60% of AVFs never mature adequately to be successfully cannulated for dialysis 16 compared to 20-25 years ago where the nonmaturation rates in AVFs was approximately 10% 12 . www.intechopen.comProgress in Hemodialysis -From Emergent Biotechnology to Clinical Practice 366 1.1.2Arteriovenous graft Arteriovenous grafts (made from polytetrafluoroethylene, a synthetic fluoropolymer of tetrafluoroethylene) are advantageous because of short maturation time and relative ease to cannulation compared to AVFs 12,[17][18][19] .Until recently, AVGs were the most common access used in hemodialysis patients in the Unites States 20 .However, the main disadvantages of AVGs are development of recurrent venous stenosis, requiring frequent interventions to maintain patency, and graft infection 19,[21][22][23][24] . Tunneled central venous catheterTunneled central venous catheters have the advantage of immediate use, multiple sites for insertion, and the ability to provide access for hemodialysis for a period of months, permitting time for AVF or AVG maturation, in patients who require immediate hemodialysis 19,[25][26][27][28] .However, the main disadvantages are the high risks of morbidity and mortality caused by infection 7,29-33 , catheter thrombosis 19,[34][35][36][37] , and central venous stenosis [37][38][39] . Epidemiology and clinical significance of hemodialysis vascular access dysfunction 2.1 Epidemiology of hemodialysis vascular accessDue to reduced AVF use and increased AVG (70% in 1993 40 ) and catheter use in the United States from the mid-1980's-1990's, the National Kidney Foundation in 1997, in an effort to improve vascular access outcomes, published the first Kidney Disease Outcome Quality Initiative (K/DOQI) clinical practice guidelines for vascular access to optimize the care of vascular access in hemodialysis patients using evidenced and opinion-based guidelines 41 .Since these initial clinical practice guidelines have been published, we have seen the creation of the Fistula First Breakthrough Initiative (FFBI) [42][43][44][45] and two more revised K/DOQI clinical practice guidelines and performance measures for vascular access 19,46 , which have clearly impacted and improved hemodialysis vascular access management.The most recent report from the 2009 United States Renal Data System (USRDS) has showed an AVF prevalence of 50% 47 , a marked improvement since 2004 (39% AVF prevalence), 2000 (30% AVF prevalence), and 1998 (26% AVF prevalence) 48 in the United States.In contrast, AVF prevalence in Europe and Japan, reported from the Dialysis Outcomes and Practice Patterns Study (DOPPS) has been historically much higher, ranging from 57-91% 20 .While the K/DOQI guidelines and FFBI have clearly played an instrumental role in meeting the initial target goal of 50% AVF prevalence (new goal 66% 19,42 ), the prevalence of CVC use continues to remain between 20-30% in the United States 42 .Furthermore, this trend of increased catheter use has also been observed in other countries, such as Spain, France, Belgium, Germany, and Italy 20 .This is likely due to an increase in the number of AVFs that have failed to mature for dialysis use in recent years 14,16 . Clinical significance and economic implications of hemodialysis vascular access dysfunctionWhen patients develop vascular access dysfunction, due to an immature AVF or thrombosed AVF or AVG, they are often consigned to CVC use for prolonged periods.Because dialysis with a catheter is associated with increased morbidity and mortality [49][50][51][52][53][54][55] , CVC use has significant clinical implications such as increased risk of bacteremia which has been reported to occur at a frequency ranging from 2.5 to 5.5 episodes per 1000-catheter www.intechopen.com