Hemodialysis vascular access: Entering a new era

Hemodialysis vascular access: Entering a new era

Of Nephrology and Nephrologists Spotlighting new and provocative developments in world nephrology and featuring nephrologists who occupy leadership ro...

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Of Nephrology and Nephrologists Spotlighting new and provocative developments in world nephrology and featuring nephrologists who occupy leadership roles

Manuel Martı´nez-Maldonado, MD Editor-at-Large

Hemodialysis Vascular Access: Entering a New Era Steve J. Schwab, MD

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EPETITIVE ACCESS to the central circulation is essential to the practice of maintenance hemodialysis.1-3 The first form of hemodialysis vascular access—trocars inserted in both the artery and the vein—were replaced by Belding Scribner’s invention of Teflon (DuPont, Wilmington, DE) catheters that were linked on the surface to form an external arteriovenous (AV) fistula. The Scribner’s shunt shortcomings, such as short use-life, and high infection and thrombosis rates, led to its replacement by the internal AV fistula. The first of these connected the radial artery with the cephalic vein at the wrist (Cimino fistula) and had the advantages of long use-life, low thrombosis rate, and very low infection rate. Its principal deficiencies were that not all patients had adequate arteries and veins to support it, and to obtain sufficient diameter and flow characteristics to make it useful took a long maturation time (Fig 1). These deficiencies led to synthetic, internal AV fistulas (AV grafts) initially composed of natural and synthetic products, polytetrafluoroethylene being the preferred synthetic material. Temporary hemodialysis catheters for immediate access to the circulation were developed in the early 1960s, and evolved to a near standard design: the coaxial, doublelumen polyurethane catheter. In the late 1980s, silastic and silicone elastomer was substituted for polyurethane, and this softer material allowed the use of a larger catheter with its tip placed in the right atrium to facilitate much faster blood flow. A bonded cuff and tunnel were developed to position the catheter to aid patient acceptance and minimize infectious complications.4 COMPLICATIONS

Complications of vascular access are a major cause of morbidity for hemodialysis patients. In xxxviii

its latest report, the United States Renal Data System (USRDS) estimates that the cost of access mortality approaches $8,000/patient at risk/ year. Conservative estimates suggest that this figure represent 17% of total spending for hemodialysis patients. Feldman and others have reported that access-related morbidity accounts for almost 25% of all hospital stays for end-stage renal disease (ESRD) patients and contributes to as much as 50% of other hospitalization costs.5 Managed care organizations planning for a capitated payment environment estimate that a quarter of the cost of end-stage renal disease effort is spent maintaining hemodialysis vascular access. This area remained largely unstudied before the mid-1980s. There were few articles devoted to vascular access, few clinical trials, no mention of hemodialysis vascular access at the national meetings of the major nephrology societies, and no abstract submission category existed for this important area. In the late-1980s, a series of prospective studies focused on the issues of thrombosis and infection, and of new access formation rates in the United States dialysis population.1-4 At the same time, the new cuffedtunneled catheter came under serious scrutiny for its role as long-term vascular access.6 Prospective studies revealed AV access survival rates of less than 2 years with thrombosis rates exceeding 1.2 episodes/patient at risk/year. Also identified were catheter infection rates that approached or exceeded one major episode of bacteremia per 6 months.6 Duke University, Washington University, the University of California San Diego, Indiana University, Ohio State University, and the Austin Clinic, to name a few, began to evaluate aggressively the problems leading to hemodialysis vascular access failure. The National Kidney Foun-

American Journal of Kidney Diseases, Vol 34, No 3 (September), 1999: pp xxxviii-xl

HEMODIALYSIS VASCULAR ACCESS

Steve J. Schwab, MD, FACP Professor and Vice Chairman Department of Medicine Co-Chief, Division of Nephrology Chief, Section of Hospital Medicine Duke University Medical Center Durham, NC

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OST nephrologists agree that caring for patients on hemodialysis therapy is most difficult. The patients are prone to multiple complications, particularly the atherosclerosis that makes access to the circulation, the sine qua non of hemodialysis, difficult and fraught with danger. The nephrology community should be thankful that caring for the lifeline has become one of Steve Schwab’s major interests. An Alpha Omega Alpha honor society graduate of the University of Missouri School of Medicine, Schwab received his internal medicine training in the University of Kansas Hospital and Clinics and his nephrologic education at Washington University School of Medicine and Barnes Hospital in St. Louis, Missouri. His initial interest in phosphate

dation’s Dialysis Outcome Quality Initiative (DOQI) on hemodialysis vascular access6 further established hemodialysis vascular access as one of the four areas where major problems in ESRD patient care existed, and where codified practice guidelines could improve patient care. More than 2,000 manuscripts were reviewed and over 220 led to the creation of the guidelines and to the development of several consensus statements. 1. Native AV fistulas that mature sufficiently have a better rate of staying patent and a lower morbidity rate compared with AV

Fig 1. Depiction of a native AV fistula. Reprinted with permission.7

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transport transmuted into the more global art of ESRD patient care. In 1987 he published his first article on the detection and care of stenoses in vascular access grafts, the subject he discusses in the accompanying article. Since then, careful analyses of the problem have continued to emerge from Schwab’s pen. He has also added significantly to our knowledge of the effects of contrast media on renal and cardiac function and to the diagnosis of renal vascular disease. Over 100 publications have contributed to his promotion to professor of medicine at Duke University. His administrative acumen and people skills have led to his appointment as co-chief of the nephrology division and vice-chair of the department of medicine. Schwab serves on numerous editorial boards, including the American Journal of Kidney Diseases, and is chief editor of the Yearbook of Nephrology and Hypertension. He has served the National Kidney Foundation with distinction, particularly in the Dialysis Outcome Quality Initiative, and he sits on the American Board of Internal Medicine’s nephrology board. Working with Steve is a delight: he is affable, precise, helpful, and considerate. In another vein, he and his wife Carol love hiking; he also plays golf, during which he assures us he doesn’t hike. —Manuel Martı´nez-Maldonado, MD

grafts. Thus, the National Kidney Foundation issued a series of guidelines designed to increase the prevalence of native AV fistulas in the North American population. Problems with the formation of native AV fistulas include late referral of patients to nephrologists, and an aging diabetic population with vascular disease and thus limited AV fistula access sites. Nevertheless, after reviewing the available data the workgroup felt that it was possible in the United States to achieve a 50% working prevalence of AV fistulas.1-4 2. Both fistula and graft AV access fail predominantly because of thrombosis, mediated in ⬎90% of the occurrences by outflow venous stenoses. In AV grafts, ⬎50% occur at or within 5 cm to 6 cm of the vein graft anastomosis. Other sites for this stenosis are areas of venous valves, vein bifurcation, and areas of previous central venous

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cannulation. Endothelial, neointimal, and fibromuscular hyperplasia are common causes of this venous stenosis. Prospective studies showed that use of early monitoring techniques to detect stenosis combined with aggressive therapeutic interventions, including percutaneous transluminal angioplasty and surgical revision, significantly extended the patency of both AV grafts and native AV fistulas.1-4 3. Silicone-cuffed catheters, although an outstanding bridge device, were inferior to AV access in terms of long-term patency and, therefore, these catheters were discouraged as permanent vascular access.4 We have entered a new era of scientific and clinical evaluation of vascular access. The National Institutes of Health is proposing requests for applications for both investigation of the basic biological causes of intimal and fibromuscular hyperplasia, and for clinical trials to determine effective ways to deal with creation and repair of AV access. Industry is developing new AV graft materials and designs. The American Society of Nephrology, the National Kidney

STEVE J. SCHWAB

Foundation, and the Renal Physicians Association have identified hemodialysis vascular access as a major investigative effort and cause of clinical concern. Once largely ignored vascular access has emerged as a leading issue for major investigative efforts to improve the care of patients with end-stage renal disease. REFERENCES 1. Fan PY, Schwab SJ: Vascular access: Concepts for the 1990s. J Am Soc Nephrol 3:1-11, 1992 2. Windus DW: Permanent vascular access: A nephrologists view. Am J Kidney Dis 21:457-471, 1993 3. Schwab SJ: Hemodialysis vascular access. Forum. Kidney Int 55:2078-2090, 1999 4. Schwab SJ, Beathard G: The hemodialysis catheter conundrum: Hate living with them, Can’t live without them. Kidney Int 56:1-17, 1999 5. U.S. Renal Data System: U.S. Renal Data System 1997 Annual Report, Chapter 4:45-67, Chapter 10, pp 143161, 1997 6. National Kidney Foundation DOQI Clinical Practice Guidelines for Hemodialysis Vascular Access. Work group: Schwab SJ, Besarab A, Beathard G, Bouwer D, Etheredge E, Hartigan M, Levine M, McCann R, Sherman R, Trerotola S. Am J Kidney Dis 30:S137-S240 (suppl 3), 1997 7. Schwabs: Principles and Practice of Nephrology. St. Louis, Mosby, 1991, p 769