At the most recent American Society of Diagnostic and Interventional Nephrology (ASDIN) annual scientific meeting (23–25 February 2024, New Orleans, USA), Gerald Beathard (University of Texas Medical Branch, Galveston, USA) closed out the first session with a presentation titled Inflow enigma—Balloon or Bowtie?
“We diagnosed cases with what we refer to as outflow stenosis,” Beathard began, “however this is actually an imbalance between the inflow and outflow.” The total outflow capacity of an access, he states, is inadequate to handle the inflow volume. This relative inadequacy of the access outflow capacity in comparison to inflow blood volume results in “increased outflow resistance and a proportional increase in intraluminal pressure”.
The point at which this occurs, however, depends on two variables, according to Beathard. “These two variables are the inflow blood flow—or Qa—and the outflow luminal diameter,” Each of these can vary considerably, he stated. “There’s a reciprocal relationship between the percent reduction in outflow luminal diameter and Qa.” This means that, as Beathard framed it, a 15% reduction in luminal diameter with a Qa of 4,000 mL/min, can cause a development of a mega-fistula and hyper pulsatility, whereas if you only have a Qa of 800 mL/min, you may have to have a 60–70% reduction in outflow luminal diameter in order to generate the same clinical picture. The adverse effects of high access blood flow, he stated, can include eccentric ventricular hypertrophy, dilatation of heart chambers, and pulmonary hypertension. It can also cause “haemodialysis dialysis access related distal ischaemia (HAIDI), aneurysmal dilatation of the AV [arteriovenous] access, and also decrease dialysis clearance efficiency because of an increase incardiopulmonary recirculation.”
Continuing the presentation, Beathard moved on to examine studies that have explored this topic. “Most studies that have dealt with excessive flow and flow reduction have waited until the patient is having serious problems—such as heart failure—before he is treated.” He, however, feels that the basic principle of medicine is to treat things before the disease happens, taking a “prophylactic approach,” which he stated is “something that we should consider in these cases”.
With that in mind, Beathard stated that he thinks that it is “critically important” that access flow measurement be a part of the evaluation of all these cases, prior to planning treatment, and then, using this information, a bimodal approach be taken; angioplasty for cases with a low or normal Qa, and flow reduction as primary treatment for cases with an elevated Qa.
In order to better manage the issues that arise from high access blood flow, Beathard, along with colleagues from various centres, have developed an algorithm that will help to simplify the decision process of which modality to use when managing this issue in AV access. “We developed [this algorithm],” he stated, “so that if you take major flow, access flow that it is in the 800 and 1500 mL/min range, management should be individualised based upon individual patients, comorbidities and situation. If it’s 800 mL/min or less, then [use] angioplasty.” If that is successful, he adds, blood flow after angioplasty should be measured to see if flow reduction is needed as a secondary procedure. This algorithm, which he presented at the 2024 ASDIN annual scientific meeting, is pending publication in the Journal of Vascular Access.
