Improving Dialysis Access Management

Improving Dialysis Access Management By Neenoo Khosla and Shubhada N. Ahya Renal replacement therapy requires either placement of a functional hemodialysis vascular access or peritoneal dialysis catheter. Early provision of a dialysis access Improves patient care with reduction In morbidity and reduces the economic burden Incurred as a result of delayed access placement. Vascular access dysfunctions (thrombosis and Infection) pose the greatest burden on the end-stage renal disease population. This article reviews the current literature on the planning of dialysis access, with particular emphasis on Issues pertaining to vascular access. Current concepts to maximize access patency and efficiently manage vascular access complications are highlighted. Copyright 2002, Elsevier Science (USA). All rights reserved.

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HE POPULATION OF patients with endstage renal disease (ESRD) increases yearly in the United States. Efficient initiation of renal replacement therapy requires preemptive placement of a hemodialysis vascular access or peritoneal dialysis catheter. Although the placement of the latter is less complicated. vascular access for hemodialysis poses several problems. Hemodialysis is the primary mode of renal replacement therapy in the United States with the most recent United States Renal Data System reporting the prevalence of hemodialysis patients at 62%.' Unfortunately, access-related complications account for 16% to 25% of hospital admissions in hemodialysis patients with a cost of over $1 billion annualIy.2.3 In the face of this problem, the Dialysis Outcomes Quality Initiative (DOQI) guidelines recommend arteriovenous fistula (A VF) be the vascular access of choice. 4 Unfortunately, it is estimated that only one third of hemodialysis patients have an AVF.!I Furthennore, in many facilities there is no routine procedure for the prospective diagnosis and treatment of access stenosis. Treatment of access thrombosis is frequently delayed with resulting hospitalizations and unnecessary catheter placement. In a global sense, the current system seems suboptimal. This review highlights recent developments in (1) hemodialysis access planning with emphasis on creation of an autogenous AVF, (2) the role of access surveillance in maintaining access patency, and (3) current strategies to improve management of accessrelated complications.

ing general principles in mind: (I) Patients should be educated preemptively to preserve superficial veins of the ann and central veins of the thorax by avoiding venipuncture and central vein cannulations. (2) An autogenous vein should be used when possible. (3) The placement of an AVF should occur before the onset of renal replacement therapy because this maximizes access patency and patient survival. 6 (4) Preoperative imaging should be used in selected cases to maximize primary patency. (5) The initial construction of an AVF should preferentially be in the distal arms to preserve more proximal sites for future accesses Early nephrology referral is not the current standard of practice. Up to 30% of dialysis patients are referred in the final month before needing hemodialysis. 9 In terms of vascular access, this is particularly problematic because the likelihood of a patent vascular access on dialysis initiation is inversely related to the number of previous consultations with a nephrologist. 8 Furthermore, use of a central catheter and premature puncture of an access system is associated with a high likelihood of access failure. 6 · 10 An AVF requires 2 to 3 months for maturation and maximal blood flows through an A VF are reached over time. The formation of vascular access therefore should occur at least by the time the serum creatinine level reaches 4 mgldL or before the creatinine clearance is below 25 mUmin. 4 A native AVF is the optimal initial vascular access with placement of a radiocephalic AVF

VASCULAR ACCESS PLANNING

From the Division of Nephrology/Hypertension. Feinberg School of Medicine, Northwestern University, Chicago, IL Address reprint requests to NutwO Khosla, MD. Division of Nephrology/Hypertension. 710 North Fiarbanks. Olson 4·500. Chicago. IL 60611. Copyright 2002, Elsevier Scienu (USA). All rights reserved. 0270·929510212206·0009$35.0010

The primary goal when placing a vascular access is to create an access with a long functional survival that also allows delivery of an adequate hemodialysis dose. An accurate initial assessment and management plan is required with the follow-

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Table 1. Evaluation Before Access Placement Patient History

PhysicaJ Examination

Previous central venous catheter Dominant arm History of pacemaker History of severe congestive heart failure History of diabetes mellitus History of anticoagulant therapy or coagulation disorder Presence of comorbidity condition that limits life expectancy (ie, malignancy) Previous access history Presence of artificial valve Previous neck or arm surgery

Characteristics of peripheral arterial pulsation Results of Allen test Bilateral upper-extremity blood pressure Evaluation of arm edema and size Examination of collateral vein Evidence of previous central or peripheral catheterization Toumiquet venous palpation Evidence of heart failure

preferred before a brachiobasilic AVF. If it is not possible to establish either of these, an arteriovenous graft (AVG) or a transposed brachiobasilic vein fistula can be placed. Numerous studies have established that an AVF provides the lowest complication rate and the longest functional survival."- 17 An AVF, however, does have a higher incidence of primary failure, ranging from 10% to 30%, as compared with an AVG.9 Primary failures are more likely to occur in the elderly, women, diabetic patients, patients with peripheral vascular disease, and patients with premature access puncture.9.18.19 Patients with such comorbid conditions may therefore require preoperative evaluation to increase the likelihood of a functional AVF. Nonetheless, if primary failures are excluded, the 5- and 10-year patencies for radiocephalic fistulas are reported to be 53% and 45% respectively.9.20 The brachiobasilic AVF has similar patency rates of 50% to 70% and 34% to 53% at 3 and 5 years, respectiveJy.16.21,22 In contrast, the cumulative patency for an AVG grafts at 1, 2, and 4 years is 67%, 50%. and 43%.\3 Similarly, fistulas have lower infectious complications with rates of 0% to 6%23 for the wrist and 8% to 10% for the elbow.24 Infection rates are higher for arteriovenous grafts (8%-19%).11.15 To determine the appropriate type of access, the vascular access surgeon usually preforms the initial preoperative investigation. Table I outlines historic and physical examination features of importance. Access placement is preferentially in the nondominant arm. A current or previous subclavian vein catheter or pacemaker is a particularly important historic feature that influences long-term access patency. Both are associated with central

vein stenosis and thrombosis in 10% to 50% of patients. 25-28 An access must not be placed on the same side as an existing subclavian vein catheter or trans venous pacer unless there are no other options available. Also. preoperative imaging of a subclavian vessel is advisable if there is a history of a previous pacemaker or catheter. The surgeon inspects the suitability of the superficial veins and the strength of the peripheral pulses. The presence of arm edema, differential arm size. and/or presence of collateral veins indicates a possible venous obstruction that may limit access placement or require preemptive correction. Preoperative imaging of the venous system is required jf the surgeon cannot assess a palpable vein or if there is a suspicion of venous obstruction. Additionally. imaging is recommended to outline the anatomy before placement of a transposed brachiobasilic AVF. Venography is currently the gold standard for preoperative imaging, providing useful information of peripheral and central vessels. Venography, however. fails to accurately characterize arterial and vein diameter measurements. Additionally. exposure to contrast agents may not be desirable in patients with significant residual renal function. Doppler ultrasound may be advantageous in such patients. 29 Preoperative ultrasound mapping accurately identifies the suitability of both the arterial and venous system and. more specificalJy, can evaluate if the cephalic vein and radial artery diameter is smaller than 1.5 to 2.0 cm.30 Such preoperative data can predict the failure of a forearm fistula. leading to creation of a primary access in the upper arm. One study prospectively assessed ultrasound vascular mapping for hemodialysis access placement and found that pre-

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operative evaluation resulted in an increase in A VF placement rate from 32% to 58%.31 Ultrasound, however, is less useful than venography in evaluating central anatomy and the interpretation of ultrasound readings is highly operator dependent. 32 Another potential noninvasive alternative to conventional venography that has been prospectively evaluated in planning access placement is magnetic resonance venography. 33 Although earlier studies indicated a lower sensitivity and specificity in detecting central thromboses, magnetic resonance venography is as useful as conventional venography. Finally, digital subtraction venography with gadolinium chelates may be an effective and safe alternative in patients with residual renal function but, again, it is less sensitive in providing data of central vessels than conventional venography.34 In summary, unless there is a suspicion of central stenosis or thrombosis, it is appropriate to use alternative imaging to venography in patients in whom it is desirable to preserve residual renal function. The choice of the alternative imaging technique depends on the experience at an individual center.

VASCULAR ACCESS MATURATION Once an A VF or A VG is established, care must be taken to maintain primary patency. Although there is little definitive data in the literature on this topic, certain measures have been recommended. A primary A VF is mature and suitable for use when the vein's diameter is sufficient to allow successful cannulation, but not sooner than I month (and preferably 3-4 mo after construction). Several measures to enhance maturation of an A VF include: (l) fistula hand-arm exercise (ie, squeezing a rubber ball with or without a lightly applied tourniquet) to increase blood flow and speed maturation; (2) selective surgical obliteration of major venous side branches to speed maturation of a slowly maturing AVF; and (3) when a new A VF is infiltrated (ie, presence of hematoma with associated induration and edema), it should be rested until swelling is resolved. A VGs should not routinely be used until 14 days after placement. Cannulation of a new A VG should not routinely be attempted, even 14 days or longer after placement. until swelling has gone down enough to allow palpation of the course of the entire graft. Ideally, 3 to 6 weeks should be allowed before cannulation of a new graft.

SURVEILLANCE Surveillance techniques that can identify A VF/ A VG impending dysfunction are critical to uninterrupted maintenance of adequate hemodialysis. In addition, it leads to lower morbidity, particularly if thrombosis is avoided because this may be further complicated by catheter placement, risk for sepsis, and hospitalization. To date, techniques available include: (J) physical examination, (2) access recirculation. (3) venous line pressure measurement, (4) access blood flow, (5) color duplex ultrasonography. and (6) contrast fistulography. Physical examination is the least expensive technique. Certain findings such as ipsilateral arm swelling suggest central venous stenosis. Prolonged bleeding after hemodialysis treatment may suggest venous stenosis warranting further evaluation. Palpation and auscultation of thrill over arterial venous segments of the access often reflect a flow of greater than 450 mUmin. whereas a pulsatile access lacking thrill reflects a lower flow rate and is often not usable for treatment without invasive evaluation followed by intervention. Positive examinations are frequently found when thrombosis has already occurred. Access recirculation occurs when dialyzed blood returning to the patient re-enters the arterial needle; this should not occur if the blood flow rate is greater than that through the dialyzer circuit. Recirculation can be detected if there is significant stenosis resulting in low blood flows. This is calculated by using the formula: (Us - Ua/Us - Uv)

x

100

Us is defined as systemic urea nitrogen, Ua as arterial blood line urea nitrogen, Uv as venous blood line urea nitrogen. Access recirculation is present when Ua is lower than Us from re-entry of dialyzed blood. This technique results in values prone to overestimation from arteriovenous disequilibrium as well as venovenous disequilibrium despite the relative ease with which this may be conducted routinely. Access recirculation measurement is no longer generally used because it is not reliably predictive of access failure and because of a lack of consensus on critical values warranting further investigation.36•37 Venous line pressure measurements (Vp) were thought to reflect possible access failure because pressures increase with intra-access stenoses. Vp

510

measurement accuracy should be perfonned systematically and consistently by using a large-bore venous needle, ensuring the absence of air and clots, and zeroing the transducer for the height difference in the system. Dynamic measurements of Vp should be perfonned with the blood flow through the dialyzer circuit of 200 to 250 mUmin for several minutes; if levels measured several times through the course of the treatment remain consistently elevated (defined by percent decline), further access evaluation is necessary. However, studies have concluded conflicting results regarding its accuracy for predicting access failure on angiography.36.38 Static Vp measurements have also been reported to be beneficial in the detection of venous stenoses. A stop-cock transducer system may be inserted between the venous needle and blood line. Fistulography should be performed if the ratio of static Vp to systemic systolic blood pressure is greater than or equal to 0.4. 39 Preliminary data has suggested that this technique and critical value has resulted in a marked reduction in access failure from thrombosis requiring replacement. 3S Access blood flow is generally considered to be the most accurate means of determining stenosis and thrombosis. Ultrasound dilution technique to measure blood flow was first described in 1995; it can be performed during hemodialysis with relative ease and are considered to be the most predictive of access dysfunction.40 Ultrafiltration is stopped, the blood pump is reduced to 300 mU min, and blood lines are reversed. A bolus of 0.9% saline is bolused through the venous port. An ultrasound flow sensor attached to the arterial line tubing measures flow via saline dilution of blood and measurement of the velocity of the ultrasound wave. Several studies have suggested that average (of 3) flow measurements by using a critical value of 600 to 700 mUmin or a drop in blood flow of 25% or more suggests stenoses warranting further investigation via fistulography.40.41 Recently, a technique using optical transcutaneous hematocrit sensor which does not require blood line reversal has been described to measure blood flow. A preliminary study suggested when done consistently in a small group of patients there was a high degree of correlation between blood flow obtained using the transcutaneous hematocrit sensor and the ultrasound dilution technique. However, further studies need to be done to determine

KHOSLA AND AHYA

this technique's accuracy in measurement in the setting of obesity, collateral blood flow, as well as its utility in assessing stenosis and thrombosis for routine surveillance.41a Doppler ultrasonography performed off hemodialysis can also determine blood flow. Measurements may be taken at multiple different locations. Pulsed-wave Doppler insonation of flow intra-access centerstrearn is made at 60° with a time average of the velocity waveform of 5 to 10 cardiac cycles. 42 Color duplex ultrasonography can also determine accurate flow measurements, however, disadvantages cited include the inability to perform the procedure at the patient's side during hemodialysis treatment, expense, and operator dependency leading to variability in measurement readings. High-frequency transducer probes give images from which velocity waveforms allow determination of blood flow intra-access. Multiple studies have confirmed its strong correlation with contrast fistulography.4.42.43 Other information that may be obtained from this particular mode of flow determination is the presence of abscess, hematomas, intraluminal thrombi, and aneurysms. Contrast fistulography is the most accurate means of determining access flow complications and affords the possibility of immediate treatment via percutaneous transluminal angioplasty. This technique also allows for detection of stenoses causing flow complications in locations beyond the venous limb of the access; fistulography can detect lesions located centrally as well as proximally outside of the access. According to DOQI "guidelines. venous stenoses associated with greater than 50% luminal narrowing on fistulography should be treated with angioplasty or surgical revision. 4 Success of percutaneous trans luminal angioplasty is determined by improvement in cross-sectional diameter of the vessel at the site of stenosis; a technically successful outcome is defined as a residual stenosis of 30% or less. Hemodynamic success is defined by an improvement in Vp or blood flow by using the techniques just described, whereas clinical success is defined by the ability to use the access for at least one HD treatment after intervention. 4 Though there may not be a unanimous consensus on the mode of surveillance. it is generally agreed that surveillance is necessary to prolong access surviVal.

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COMPLICATIONS

The major complications of vascular accesses include thrombosis, poor flow secondary to venous stenosis, and less commonly arterial stenosis, infection, and vascular steal syndrome. Although access surveillance techniques are intended to predict and pre-emptively prevent thrombosis, current techniques are not highly sensitive. Venous neointimal hyperplasia accounts for the overwhelming majority of pathology in access failure. Macrophage activity, specific cytokines such as plateletderived growth factor, and angiogenesis within the neointima and adventitia are likely to contribute to the pathogenesis of venous neointimal hyperplasia. 44 Interventions that are aimed toward these mediators may prevent thrombosis. At present, there are not clearly effective pharmacologic therapies to prevent either neointimal hyperplasia or thrombosis. A recent, small, randomized, controlled trial evaluated the use of fish oil in preventing thrombosis in newly constructed arteriovenous grafts. 45 Omega 3 fatty acids contained in fish oil are known to inhibit cyclooxygenase and therefore may also inhibit intimal hyperplasia. In this study, 24 patients were randomized to receive 4,000 mg of fish oil or 4,000 mg of control oil. Patients were followed-up within 2 weeks of graft placement and monitored for 12 months or until a thrombotic event. One-year primary patency rates were 14.9% for the control group and 75.6% for the fish oiltreated group. This study, though impressive, is small and warrants further investigation. The role of antithrombotic agents, such as warfarin, aspirin, and dipyridamole, in thrombosis prevention is largely unclear. Warfarin may be useful for recurrent thrombosis without an anatomic stenosis. 46 A trial comparing aspirin and dipyridamole found the latter to be helpful in preventing thrombosis in new grafts but not helpful in patients with previous thrombosis. 47 Hence, without effective preventive therapy, thrombosis remains the primary cause of up to 80% of access failures. Management considerations of thrombosis, infection, and steal are individually considered here. Thrombosis

The type of access and the site of thrombosis influence the success of access salvage. In over 85% of cases the underlying cause of thrombosis is a stenosis. 2•4.11 Stenosis accompanied by thrombosis is more difficult to treat than stenosis detected

by prospective monitoring. There are no randomized trials comparing surgical intervention with percutaneous treatment of clotted accesses. Surgical or percutaneous thrombectomy, however, are considered to have similar initial declotting success rates and the decision between either generally rests in the technology available at an individual center. AVF thrombosis is more difficult to treat than AVa thrombosis but can be successfully treated if intervention is prompt (with greater longterm patency rates). The initial success rate of percutaneous dec lotting of a thrombosed AVF is over 90%.48.S2 Although primary patency rates at 1 year are lower (50%-60%), I-year secondary patency rates are excellent at 80%. Of note, results of percutaneous declotting of forearm fistulas are superior to results of upper-arm fistulas. Primary patency rates at I year for the latter are reportedly as low as 27%.49.50 Also. results are markedly dependent on the length of the lesion, with lesions greater than 2.0 em 5 times more likely to have loss of patency as compared with lesions less than 2.0 cm.SO Although the initial success of declotting a thrombosed graft is greater (95%-99%), long-term patency rates are markedly inferior to that of declotted fistulae. Six-month and I-year patency rates are 32% and 8%, respectively.s2'ss Time to reintervention on a thrombosed Ava is short with a median interval of 6.39 months as compared with a forearm A VF (18 mo) and upper-arm A VF (8.57 mo).50 Access surveillance of declotted grafts therefore must be more frequent as compared with declotted fistulas. These data again highlight the need for aggressive attempts to place an AVF as the primary means for vascular access in hemodialysis patients. Infection

Infection is also a complication of arteriovenous access though it is higher in patients with tunneled catheters. The most common organisms causing bacteremia are Staphylococcus aureus and S. epidermidis. One should have heightened suspicion for an infected access in patients with recent interventional or surgical manipulation, perifistula hematomas, or pseudoaneurysms; the access should be palpated for warmth. erythema, and tenderness. In the setting of negative cultures. one approach is to empirically treat for 3 weeks with antibiotics. A thrombosed AVG may serve as a nidus for infec-

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tion; one particular study performed indium scans in a series of patients with thrombosed AVOs and fever and found an infected clot in each case when surgically removed..56 To date, DOQI guidelines recommend for infected AVFs completion of a 6-week course antibiotics and incision and debridement as necessary. Infection of AVOs requires directed antibiotic therapy as well as surgical consultation for resection or complete removal (absolute indication if AVO placed with 1 mo of infection). If fever and/or bacteremia persist after appropriate debridement or removal further, investigation with echocardiogram or spinal imaging is warranted to determine the presence of endocarditis or osteomyelitis..57.~8 Vascular Steal

The syndrome of vascular steal occurs when arterial flow is shunted back to the heart resulting in distal limb ischemia. This phenomenon occurs most frequently with lower limb AVOs but also, to a lesser extent, with brachial artery fistulas. Patients with diabetes and/or those with abnormal arterial supply caused by prior vascular access, vascular anomalies, and/or atherosclerotic disease are at greatest risk for ischemia. Limb ischemia secondary to an arteriovenous access can develop at any time from a few hours to months after construction. Symptoms of steal vary from sensations of numbness, tingling, and coldness to acute nerve ischemia. The latter requires immediate ligation of the access. In other circumstances an angiogram can be performed to identify proximal lesions amenable to angioplasty. In many patients the symptoms are mild and abate with time. Often wearing a glove, particularly during hemodialysis. may alleviate symptoms. If symptoms persist or progress, however, banding or, in refractory cases, ligation of the fistula may be required. CONCLUSION

Multiple studies have shown that native AVF placement improves access patency and longevity. Patients who have been determined to be near ESRD by the nephrologist should be referred to the access surgeon for fistula placement in a timely manner. These goals are certainly achievable, as several countries in Europe such as France, Germany, Italy, Spain, and the United Kingdom have shown. A recent comparison of these countries with the United States by using data from the

Dialysis Outcomes and Practice Patterns Study included the examination of patterns of vascular access use, with the use of AVF in new hemodialysis patients in these European countries ranging from 47% to 83% compared with 15% in the United States. The study cited differences in population characteristics such as race, diabetes status, peripheral vascular disease status, and angina history that may contribute to the differences in AVF placement. Further, 69% of patients initiated on hemodialysis were seen by a nephrologist for more than 1 year in Europe compared with 44% in the United States (P < .0(01).59 These important comparisons certainly suggest that early referral to a nephrologist is critical for optimization of pre-ESRD care. Interestingly, significant differences persisted with the placement of more temporary accesses in the United States than in Europe. whereas both had similar percentages of patients under the care of a nephrologist for greater than 30 days, suggesting that type of access placement should become more of a priority in the US nephrology practice than it currently is and that access surgeons (and trainees) should be experienced in the placement of a permanent access that will mature and function at the time of hemodialysis initiation. Finally, a preESRD program in which the patient is educated on the importance of a functional permanent access at the time of hemodialysis initiation may increase placement. Once the access has been placed and hemodialysis initiation is declared, serial monitoring of the access should be an important part of the care provided by the hemodialysis unit. This can only be achieved by communication between the nephrologist and team at the dialysis unit, the interventional radiologist, and the access surgeon. Continued interest and research in areas such as optimal access monitoring mode as well as prevention of common complications such as thrombosis and stenosis can only lead to better care for the hemodialysis patient and, hopefully, an improvement in health care cost. REFERENCES 1. United States Renal Data System: USRDS 2001 Annual Data Report. 1be National Institutes of Diabetes and Digestive and Kidney Diseases. Bethesda. MD. 2001 2. Feldman HI. Kobrin S. Wasserstein A: Hemodialysis vascular access morbidity. J Am Soc Nephrol 7:523-535. 1996 3. Feldman HI. Held PJ. Hutchinson JT. et aI: Hemodialysis vascular access morbidity in the United States. Kidney Int 43:1091-1096. 1993

ACCESS 4. NKF-KIDOQI Clinical Practice Guidelines for Vascular Access: Update 2000. Am J Kidney Dis 37:S137-SI8I, 2001 (suppl I) 5. Pisoni RL. Young EW, Dykstra OM. et a1: Vascular access use in Europe and the United States: results from the DOPPS. Kidney lnt 61:305-316,2002 6. Lameire N, Van Biesen W: The pattern of referral of patients with end-stage renal disease to the nephrologist-a European survey. Nephrol Dial Transplant 14:16-23, 1999 (suppl6) 7. Arora P. Obrador GT. Ruthazer R. et al: Prevalence, predictors and consequences of late nephrology referral at a tertiary care center. J Am Soc Nephrol 10:1281-1286, 1999 8. Stehman-Breen CO, Sherrard OJ, Gillen 0, et al: Determinants of type and timing of initial permanent hemodialysis vascular access. Kidney Int 57:639-645, 2000 9. Rodriguez JA, Armadans L. Ferrer E. et al: The function of permanent vascular access. Nephrol Dial Transplant 15:402408. 2000 10. Friedman AL, Walwonh C, Meehan C, et al: First hemodialysis access selection varies with patient acuity. Adv Ren Replace Ther 7:54-S 10, 2000 II. Palder, SB, Kirkman RL. Whittemore AD, et a1: Vascular access for hemodialysis: Patency rates and results of revision. Ann Surg 202:235-239. 1985 12. Harland RC: Placement of permanent vascular access devices: Surgical considerations. Adv Ren Replace Ther 1:99106. 1994 13. Munda R, First MR, Alexander JW, et al: Polytetrafluoroethylene graft survival in hemodialysis. JAMA 249:219,1983 14. Kinnaert P. Vereerstraeten p, Toussaint C, et al: Nine years' experience with internal arteriovenous fistulas for haemodialysis: A study of some factors influencing the results. Br J Surg 64:242, 1977 15. Kherlakian GM. Roedersheimer LR, Arbaugh JJ. et al: Comparison of autogenous fistula versus expanded polytetrafluoroethylene graft fistula for angioaccess in hemodialysis. Am J Surg 152:238. 1986 16. Dunlop MG, Mackinlay JY. Ienkins AM: Vascular &Cce~s: Experience with the brachiocephalic fistula. Ann R Coli Surg Engl 68:203. 1986 17. Ryan II. Dennis MI: Radiocephalic fistula in vascular access. Br I Surg 77:1321. 1990 18. Miller PE, Tolwani A, Luscy CP, et a1: Predictors of adequacy of arteriovenous fistulas in hemodialysis patients. Kidney Int 56:275. 1999 19. Silva MB Ir, Hobson RW 2nd, Pappas PI, et a1: A strategy for increasing use of autogenous hemodialysis access procedures: Impact of preoperative noninvasive evaluation. I Vasc Surg 27:302, 1998 20. Bonalumi U. Civalleri 0, Rovida S, et al: Nine years' experience with end-to-end arteriovenous fistula at the 'anatomical snuffbox' for maintenance haemodialysis. Br J Surg 69: 486, 1982 21. Livingston CK, Potts JR: Upper arm arteriovenous fistulas as a reliable access alternative for patients requiring chronic hemodialysis. Am Surg M :1038-1042, 1999 22. Cole O. Rigg K: The use of brachial arteriovenous fi stulas for hemodialysis. Clin Nephrol 49:203, 1998 23. Reilly DT. Wood RFM, BeIl PRF: Prospective study of

513 dialysis fistulas : Patient problems and their treatment. Br I Surg 69:549-553. 1982 24. Bender MH. Bruyninckx CM. GerJag PG: The brachiocephalic elbow fistula: A useful alternative angioaccess for permanent hemodialysis. J Vasc Surg 20:808-813, 1994 25. Korzets A, Chagnac A, Ori Y. et al: Subclavian vein stenosis, permanent cardiac pacemakers and the haemodialysed patient. Nephron 58: 103-105, 1991 26. Chuang CL, Tarng DC, Yang WC. et al: An occult cause of arteriovenous access failure: Central vein stenosis from permanent pacemaker wire. Report of three ca.~es and review of literature. Am J Nephrol 21 :406-409. 2001 27. Schwab SJ, Quarles LD. Middleton JP, et al : Hemodialysis-associated subclavian vein stenosis. Hemodialysis-associated subclavian vein stenosis. Kidney Int 33:1156-1159, 1988 28. Hernandez D, Diaz F, Ruffino M, et al: Subclavian vascular access stenosi~ in dialysis patients: Natural history and risk factors. I Am Soc Nephrol 9:1507-1510. 1998 29. Silva MB. Hobson RW, Pappas PJ: A strategy for increasing use of autogenous hemodialysis access procedures: Impact of preoperative noninvasive evaluation. J Vasc Surg 27:307-308, 1998 30. Brimble KS, Rabbat CG, Schiff D: The clinical utility of Doppler ultrasound prior to arteriovenous fistula creation. Semin Dial 14:314-317.2001 31. Robbin ML, Gallichio MH. Deierhoi MH, et al: US vascular mapping before hemodialysis access placement. Radiology 217:83-88, 2000 32. Gooding GA, Woodruff A: Color Doppler imaging in the subclavian-axillary region and upper extremity. Clin Imaging 18:165-172, 1994 33. Menegazzo D, Laissy IP, Durrbach A. et al: Hemodialysis access fistula creation: Preoperative assessment with MR venography and comparison with conventional venography. Radiology 209:723-728, 1998 34. Geoffroy 0, Tassart M, Le Blanche AF. et al: Upper extremity digital subtraction venography with gadoterate meglumine before fistula creation for hemodialysis. Kidney Int 59: 1491-1497. 2001 35. Besarab A, Lubkowski T, Frinak S, et al: Detection of access strictures and outlet stenoses in vascular accesses. Which test is best? ASAIO J 43:M543-M547. 1997 36. Sullivan KL. Besarab A, Bonn J, et al: Hemodynamics of failing dialysis grafts. Radiology 186:867-872, 1993 37. Besarab A. Lubkowski T, Frinak S, et al: Detecting vascular access dysfunction. ASAIO J 43:MS39-M543, 1997 38. BOllman Pl. Boereboom FT, Smits HF. et al: Pressure or flow recordings for the surveillance of hemodialysis grafts. Kidney Int 52:1084-1088, 1997 39. May RE, Himmelfarb J, Yenicesu M, et al: Predictive measures of vascular access thrombosis: A prospective study. Kidney Int 52: 1656-1662, 1997 40. Krivitski NM: Novel method to measure access flow during hemodialysis by ultrasound velocity dilution technique. ASAIO I 41:M741-M74S, 1995 41. Yarar D, Cheung AK. Sakiewicz P, et al: Ultrafiltration method for measuring vascular access How rates during hemodialysis. Kidney Int 56: 1129-1135. 1999 41a. Steuer RR. Miller DR. Zhang S. et al: Noninvasive transcutaneous determination of access blood flow rate. Kidney Int 60:284-291, 2001

514 42. Finlay DE. Longley 00, Foshager MC, et al: Duplex and color Doppler sonography of hemodialysis arteriovenous fistulas and grafts. Radiographics 13:983, 1993 43. Weitzel WF. Rubin 1M. Swanz RD. et al: Variable flow Doppler for hemodialysis access evaluation: Theory and clinical feasibility. ASAIO J 46:65-69, 2000 44. Roy-Chaudhury p, Kelly BS, Miller MA, et al: Venous neointimal hyperplasia in polytetrafluorethylene dialysis grafts. Kidney Int 59:2325-2334. 2001 45. Schmitz po, Mccloud LK. Reikes ST, et al: Prophylaxis of hemodialyzed graft thrombosis with fish oil: Double blind. randomized prospective trial. J Am Soc Nephrol 13: 184-190, 2002 46. Schwab SJ. Harrington IT. Singh A, et al: Vascular access for hemodialysis. Kidney Int 55:2078-2090. 1999 47. Sreedhara R, Himmelfarb 1, Hakim R, et al: Anti-platelet therapy in graft thrombosis: Results of a prospective. randomized. double-blind study. Kidney Int 45:1477-1483. 1994 48. Rodrigues LT. Pengaloan J. Blanchard D. et aI: Treatment of stenosis and thrombosis in hemodialysis fistulas and grafts by interventional radiology. Nephrol Dial Transplant 15:2029-2036,2000 49. Turmel RL, Pengloan J, Blanchard D. et al: Treatment of failed native arteriovenous fistulae for hemodialysis by interventional radiology. Kidney Int 57:1124-1140. 2000 SO. Clark TW, Hirsh DA, LeBlanc 1: Outcome and prognostic factors of restenosis after percutaneous treatment of native hemodialysis fistulas. J Vase Interv Radiol 13:51-59.2002 51. Rocek M. Peregrin IH. Slaviokova M: Mechanical

KHOSLA AND AHYA thrombolysis of thrombosed hemodialysis native fistulas with use of the Arrow-Trerotola percutaneous thrombolytic device: Our preliminary experience. J Vasc lnterv Radiol 11: 11531158,2000 52. Rodrigues LT, Pengaloan 1, Bourquelot P: Interventional radiology in hemodialysis fistulae and grafts: A multidisciplinary approach. Cardio Intervent Radiol 25:3-16.2002 53. Lilly RZ, Carlton D. Barker J, et aI: Predictors of arteriovenous graft patency after radiologic intervention in hemodialysis patients. Am 1 Kidney Dis 37:945-953. 2001 54. Zaleski GX. Funaki B. Rosenblum I, et aI: Metallic stents in synthetic arteriovenous hemodialysis grafts. AJR Am J Roentgenol 176,2001 55. Middlebrook MR, Amygdalos MA. Pentecost MJ. et al: Thrombosed hemodialysis grafts: Percutaneous mechanical balloon declotting versus thrombolysis. Radiology 196:73-77, 1995 56. Ayus IC, Sheikh-Hamad D. Silent infection in clotted hemodialysis access grafts. J Am Soc Nephrol 9:1314. 1998 57. Tordoir JH. Hennan 1M, Kwan TS. et aI: Long-tenn follow-up of the polytetraftuoroethylene (PTFE) prosthesis as an arteriovenous fistula for haemodialysis. Eur J Vase Surg 2:3, 1988 58. Albers FJ: Clinical considerations in hemodialysis access infection. Adv Ren Replace Ther 3:208. 1996 59. Pisoni RL. Young EW. Dykstra DM, et al: Vascular access use in Europe and the United States: Results from the DOPPS. Kidney Int 61:305-316.2002