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NDT Advance Access originally published online on September 27, 2006
Nephrology Dialysis Transplantation 2006 21(12):3362-3363; doi:10.1093/ndt/gfl562
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© The Author [2006]. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Trials and trade-offs in haemodialysis vascular access monitoring

Talat Alp Ikizler1 and Jonathan Himmelfarb2

1Department of Medicine, Division of Nephrology, Vanderbilt University Medical Center, Nashville, TN and 2Department of Medicine, Division of Nephrology, Maine Medical Center, Portland, ME, USA

Correspondence and offprint requests to: T. Alp Ikizler, MD, Vanderbilt University Medical Center, 1161 21st Ave. South & Garland, Division of Nephrology, S-3223 MCN, Nashville, TN 37232-2372, USA. Email: alp.ikizler{at}vanderbilt.edu

Keywords: angioplasty; haemodialysis vascular access; monitoring; thrombosis

There are currently more than 300 000 patients receiving haemodialysis in the US and similar numbers are estimated in Europe. Despite the recognition that vascular access is the ‘Achilles heel’ of the dialysis procedure, haemodialysis vascular access failure and related complications continue to be one of the most difficult obstacles in the optimal care of dialysis patients. In the US, haemodialysis vascular access procedures and complications account for more than 20% of hospitalizations of haemodialysis patients and result in more than $1 billion per year of government paid expenditures [1]. Additional, often unrecognized costs stem from missed treatments, the placement and use of dialysis catheters and the significant inconvenience and anxiety endured by the patients.

There have been several initiatives to improve vascular access survival, including publication of several clinical practice guidelines (such as the Kidney Disease Outcome Quality Initiative, or KDOQI) and the Fistula First initiative, spawned by the Centers for Medicare and Medicaid Services in the US [2]. Among other recommendations such as timely and increased placement of AVF, these practice guidelines also suggest periodic monitoring of vascular access for early recognition of impending failure. Despite the fact that this recommendation is opinion based, there has been a general trend towards implementing a vascular access blood flow (VABF)-based monitoring program in many dialysis programs. The clinical utility of such an approach has been challenged by the reported results from several underpowered randomized clinical trials that have not demonstrated clinical benefit with VABF monitoring approaches [3]. Not surprisingly, there is an ongoing controversy regarding the beneficial effects of VABF monitoring, both in terms of overall access survival and associated costs.

What is the optimal monitoring method for assessment of haemodialysis access function? The KDOQI guidelines recommend several monitoring techniques including recirculation measurement, dynamic and static venous pressure monitoring and vascular access blood flow measurements [2]. Several of these methods, such as recirculation and dynamic venous pressure monitoring, are of largely historical importance and are not recommended any more for clinical practice due to low sensitivity or specificity. Static venous pressure monitoring is rarely utilized, primarily due to its cumbersome methodology and other questions about efficacy. Use of Doppler has not achieved widespread utilization, primarily due to cost and operator dependency. Currently, the most commonly utilized monitoring technique is the use of vascular access blood flow measurements by ultrasound dilution technique. Nonetheless, only a few studies have directly compared VABF to other techniques to determine positive and negative predictive value. In these limited studies, VABF appears to be superior to other techniques, substantiating its common use [4].

Does VABF monitoring improve access survival? The landmark studies by Schwab et al. and the subsequent studies by multiple other investigators clearly indicate that access monitoring can decrease thrombosis rates, both in grafts and fistulae, albeit with a more apparent beneficial effect in the former [5–7]. Accordingly, the common use of VABF is more efficient in programmes with higher prevalence of arteriovenous grafts, as commonly observed in the US. It has been speculated that the improvement in primary assisted access patency rates (i.e. time to first clotting event with or without endovascular or surgical intervention) would also improve the secondary access failure rates, namely the time to complete access failure. Despite these general expectations, several well-designed, randomized clinical trials have failed to prove this hypothesis, albeit with relatively small sample size [3,8]. These conflicting observations regarding primary vs secondary access patency with the use of VABF is further corroborated by a study by Wijnen et al. [9] published in this issue of NDT. Specifically, the authors investigated the number and costs of vascular access interventions in two separate time periods (1996–98 and 2001–03), which differ by the use of VABF monitoring during the latter period. They demonstrated a significant reduction in the number of surgical thrombectomy procedures during the VABF monitoring period, indicating a decreased frequency of thrombosis. In addition, the rate of angiograms with restorative angioplasty was higher during VABF monitoring, showing the increased accuracy in detecting significant stenosis in accesses. Consistent with other recently published data, the rate of complete access failure was not significantly different during these observation periods. Thus, for Wijnen and colleagues [9], VABF monitoring led to a trade-off of angioplasty for thrombectomy without long-term effects on access survival.

Is there a cost-benefit from the trade-off provided by vascular access blood flow monitoring? This depends on the relative cost and frequency of each requisite procedure in the healthcare system under study. In the study by Wijnen and colleagues [9], access-related costs tended to be lower during VABF monitoring, albeit the significance was apparent only for grafts and not fistulae. This is not unexpected as functional grafts are more likely to stenose and require more interventions than functional fistulae [10]. They also noted that the significant increase in angioplasty-related expenses were offset by decreased hospitalization days that were required in the event of thrombosis-related surgical procedures. Clearly, these data cannot be universally generalized to other patient populations and healthcare systems where thrombectomy is performed mostly at the out-patient setting and where associated costs have significantly decreased over the last several years. Overall, the data from this study are consistent with a previous report by McCarley et al. [5] showing significant cost savings with VABF monitoring, along with a significant improvement in catheter placement and missed outpatient treatments. Regrettably, Wijnen and colleagues did not report any data on rates of permanent and temporary catheter placement or data on the number of out-patient treatments missed.



   Prevention of vascular access failure: what is the next step?
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 Prevention of vascular access...
Acknowledgements
 References
 
While a trade-off of more angioplasties for fewer surgical thrombectomies may be cost-effective and beneficial to patient care even in the absence of an improvement in secondary access patency, clearly much more benefit could be derived if better treatments for access stenosis were developed. For the vast majority of stenotic dialysis access grafts and in a large number of stenotic arteriovenous fistulae, the pathobiological culprit is a process of venous intimal hyperplasia [11]. Unfortunately, angioplasty, by causing further injury to the vascular wall, may actually accelerate this disease process [12]. Currently, there are a number of pharmacological, as well as cellular and molecular engineering, approaches being investigated for retarding or regressing the development of venous intimal hyperplasia [13–15]. Should novel clinical therapies with utility in the treatment of intimal hyperplasia become clinically available, then the cost–benefit ratio for haemodialysis access monitoring will probably increase dramatically and current trade-off dilemmas will become historical.



   Acknowledgements
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 Prevention of vascular access...
 Acknowledgements
References
 
This work is partly supported by National Institute of Health Grant # 2 U01 DK058996.

Conflict of interest statement. None declared.

(See related article by Wijnen et al. Impact of a quality improvement programme based on vascular access flow monitoring on costs, access occlusion and access failure. Nephrol Dial Transplant 2006; 21: 3514–3519.)



   References
Top
 Prevention of vascular access...
 Acknowledgements
 References
 

  1. Allon M and Robbin ML. (2002) Increasing arteriovenous fistulas in hemodialysis patients: problems and solutions. Kidney Int 62:1109–1124.[CrossRef][ISI][Medline]
  2. 2001 NKF-DOQI clinical practice guidelines for vascular access: update. Am J Kidney Dis (2000) 37:S137–S181.
  3. Moist LM, Churchill DN, House AA, et al. (2003) Regular monitoring of access flow compared with monitoring of venous pressure fails to improve graft survival. J Am Soc Nephrol 14:2645–2653.[Abstract/Free Full Text]
  4. May RE, Himmelfarb J, Yenicesu M, et al. (1997) Predictive measures of vascular access thrombosis: a prospective study. Kidney Int 52:1656–1662.[ISI][Medline]
  5. McCarley P, Wingard RL, Shyr Y, Hakim RM, Ikizler TA. (2001) Vascular access blood flow monitoring reduces access morbidity and costs. Kidney Int 60:1164–1172.[CrossRef][ISI][Medline]
  6. Sands JJ, Jabyac PA, Miranda CL, Kapsick BJ. (1999) Intervention based on monthly monitoring decreases hemodialysis access thrombosis. Asaio 45:147–150.[ISI][Medline]
  7. Schwab SJ, Oliver MJ, Suhocki P, McCann R. (2001) Hemodialysis arteriovenous access: detection of stenosis and response to treatment by vascular access blood flow. Kidney Int 59:358–362.[CrossRef][ISI][Medline]
  8. Dember LM, Holmberg EF, Kaufman JS. (2004) Randomized controlled trial of prophylactic repair of hemodialysis arteriovenous graft stenosis. Kidney Int 66:390–398.[CrossRef][ISI][Medline]
  9. Wijnen . (2006) Nephrol Dial Transplant.
  10. Hakim R and Himmelfarb J. (1998) Hemodialysis access failure: a call to action. Kidney Int 54:1029–1040.[CrossRef][ISI][Medline]
  11. Himmelfarb J. (1999) Pharmacologic prevention of vascular access stenosis. Curr Opin Nephrol Hypertens 8:569–572.[CrossRef][ISI][Medline]
  12. Chang CJ, Ko PJ, Hsu LA. (2004) Highly increased cell proliferation activity in restenotic hemodialysis vascular access after percutaneous transluminal angioplasty: implication in prevention of stenosis. Am J Kidney Dis 43:74–84.[CrossRef][ISI][Medline]
  13. Dixon BS, Beck GJ, Dember LM, et al. (2005) Design of the Dialysis Access Consortium (DAC) Aggrenox Prevention of Access Stenosis Trial. Clin Trials 2:400–412.[Abstract/Free Full Text]
  14. Dember LM, Kaufman JS, Beck GJ, et al. (2005) Design of the Dialysis Access Consortium (DAC) Clopidogrel Prevention of Early AV Fistula Thrombosis Trial. Clin Trials 2:413–422.[Abstract/Free Full Text]
  15. Vogel PM and Parise C. (2004) SMART stent for salvage of hemodialysis access grafts. J Vasc Interv Radiol 15:1051–1060.[ISI][Medline]
Received for publication: 22. 8.06
Accepted in revised form: 23. 8.06


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