A significant number of arteriovenous fistulae (28 to 53%) never mature to support dialysis. Often, renal physicians and surgeons wait for up to 6 months and even longer hoping that the arteriovenous fistula (AVF) will eventually grow to support dialysis before declaring that the AVF has failed. In the interim, if dialysis is needed, then a tunneled catheter is inserted, exposing the patient to the morbidity and mortality associated with the use of this device. In general, a blood flow of 500

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... /min and a diameter of at least 4 mm are needed for an AVF to be adequate to support dialysis therapy. In most successful fistulae, these parameters are met within 4 to 6 wk. Most important, commonly encountered problems (stenosis and accessory veins) that result in early AVF failure can be diagnosed easily with skillful physical examination. Recent studies have indicated that a great majority of fistulae that have failed to mature adequately can be salvaged by percutaneous interventions and become available for dialysis. Early intervention regarding identification and salvage of a nonmaturing AVF is critical for several reasons. First, an AVF is the best available type of access regarding complications, costs, morbidity, and mortality. Second, this approach minimizes catheter use and its associated complications. Finally, access stenosis is a progressive process and eventually culminates in complete occlusion, leading to access thrombosis. In this context, the opportunity to salvage the AVF that fails early may be lost. This report reviews the process of AVF maturation and suggests a strategy for when and how to intervene to identify and salvage AVF with early failure. Why do some fistulae mature whereas others do not? To answer this question, one needs to understand the changes that occur at a hemodynamic, anatomic, molecular, and functional level after the creation of an arteriovenous anastomosis (12,20 -43). The single most important determinant of all of the above and consequently of AVF maturation, however, is likely to be the response of both the feeding artery and the draining vein to the increase in shear stress that occurs after the creation of an arteriovenous anastomosis (12,20,24 -26,35). Shear stress is defined mathematically by the formula 4Q/ r 3 , where is blood viscosity, Q is blood flow, and r is vessel radius (24). At a conceptual level, the shear stress rate is an indicator of the difference in velocity between the center of the Published online ahead of print. Publication date available at www.cjasn.org.