Table 2: Randomized controlled trials of arteriovenous ﬁstula surveillance. Control group Treatment group Reduce thrombosis Prolong survival 68 40 30 36 69 63 32 43 ∗ Yes Yes Yes ∗ ∗ ∗ Yes 3 International Journal of Nephrology Name Polkinghorne et al.[15] Sands et l. [16] Tessitore et al. [17] Survey method Qa (<550 mL/min) and Clinical criteria versus Clinical criteria alone Qa (<800 mL/min), Static venous pressure and Doppler ultrasound versus Doppler ultrasound alone Qa (<850 mL/min), Qb, Ru, and Rhd Preemptive angioplasty/surgical revison No No Yes Yes Tessitore et al. [18] Qa (<750 mL/min), Qb, and Ru ∗ Data/values not reported or unavailable. Qa: vascular access ﬂow, Qb: blood ﬂow, Ru: urea-based access recirculation, and Rhd: ultrasound dilution recirculation. were also higher in the functional subgroup compared to the failing one (P = 0.033). This study showed that early intervention on stenotic AVFs leads to increased longevity. If intervention is delayed until Qa ﬂow is too low, then the AVF was not as salvageable with intervention. When, then, is the appropriate time to intervene? Should prophylactic correction of subclinical stenosis become uni- versal when a low Qa is detected? The two trials that eval- uated preemptive treatment of subclinical stenosis showed decreased thrombosis rates [17, 18]. In both trials, the majority of patients were sent to angiography, because their Qa was <850 mL/min or 750 mL/min, further validating the importance of using a surveillance program. The current guidelines recommend correction only in poorly functioning AVFs that are causing clinical compromise [6]. These trials show that preemptive treatment of stenosis detected by surveillance, prior to clinical consequences, is beneﬁcial and in one trial [18], preemptive treatment was better when the Qa > 350 mL/min. Once the Qa became lower than this threshold, the access was past the point of repair. One of the major limitations of universally recom- mending preemptive intervention is that there is a paucity of information on long-term survival, as only one study evaluated this [18]. Even in that study, over a quarter of the treatment group underwent surgical revision as opposed to PTA [19] that may have contributed to these AVFs surviving longer. In fact, one study [16] revealed an increased restenosis rate after PTA. The key question of whether detection of stenosis and early intervention increases the longevity of AVFs is unfortu- nately still not answered. Even though thrombosis rates have been lower in all studies, if there is no correlation to longer AVF survival, the beneﬁcial eﬀect may be inconsequential. If there is no beneﬁt of access survival with surveillance, increased studies and interventions only consume more resources and add to cost. The method of repair (PTA or surgical) is also relevant. Although the available information suggests a beneﬁt with surveillance, there needs to be larger, powered randomized trials on the long-term survival of AVF to conclusively settle the issue of the use of surveillance leading to longer AVF survival. 3. Conclusion Observational studies have shown mixed results for the use of Qa surveillance in preventing AVF thrombosis. Randomized controlled trials, though, have shown that Qa surveillance is beneﬁcial in revealing subclinical stenosis. Preemptive angioplasty and surgical revision have shown to decrease thrombosis rates. Larger, randomized controlled trials need to be done to show whether preemptive treatment equates to improved long-term AVF survival. References [1] US Renal Data System: USRDS Annual Data Report, The National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Disease, Bethesda, Md, USA, 2010. [2] M. Allon and M. L. Robbin, “Increasing arteriovenous ﬁstulas in hemodialysis patients: problems and solutions,” Kidney International, vol. 62, no. 4, pp. 1109–1124, 2002. [3] W. L. Whittier, “Should arteriovenous access ﬂow undergo regular surveillance?” Seminars in Dialysis, vol. 24, no. 4, pp. 389–390, 2011. [4] W. L. Whittier, “Surveillance of hemodialysis vascular access,” Seminars in Interventional Radiology, vol. 26, no. 2, pp. 130– 138, 2009. [5] W. L. Whittier, H. A. Mansy, D. R. Rutz, A. M. Lewis, and R. H. Sandler, “Comparison of hemodialysis access ﬂow measurements using ﬂow dilution and in-line dialysance,” ASAIO Journal, vol. 55, no. 4, pp. 369–372, 2009. [6] National Kidney Foundation K/DOQI, “Clinical Practice Guideline and Clinical Practice Recommendations for vascu- lar access 2006,” American Journal of Kidney Disease, vol. 48, supplement 1, pp. S176–S273, 2006. [7] M. Allon, “Do we really need periodic monitoring of vascular access for hemodialysis,” Nephrology Self-Assessment Program, vol. 6, pp. 111–116, 2007. [8] E. Wijnen, N. Planken, X. Keuter et al., “Impact of a quality improvement programme based on vascular access ﬂow monitoring on costs, access occlusion and access failure,” Nephrology Dialysis Transplantation, vol. 21, no. 12, pp. 3514– 3519, 2006. [9] H. Shahin, G. Reddy, M. Sharafuddin, D. Katz, B. S. Franzwa, and B. S. Dixon, “Monthly access ﬂow monitoring with increased prophylactic angioplasty did not improve ﬁstula