Vasc‑Alert is often compared to flow-based technologies such as the Transonic device and Fresenius On-Line Flow as incorporated in the K machine. While all three methods are deemed acceptable by the latest K/DOQI report on access site maintenance, (http://www.kidney.org/professionals/KDOQI/guideline_upHD_PD_VA/index.htm), there are indications that Vasc‑Alert is both more sensitive to changes in the growth of stenosis than flow based technologies, and seems to identify issues earlier than flow based technologies:

An independent study, published at ASN in 2006, compared Vasc‑Alert and Transonic.
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This paper examines the sensitivity of both Vasc‑Alert and Transonic to detect a change in stenosis. It examines 529 interventions and compares the readings taken before to the readings taken after an intervention. The ability to detect change is a marker for the growth of stenosis. Since the fact that an intervention creates a big change in the occlusion of the stenosis (decreasing the blockage), by presumption, the device that is more sensitive here, will also be more sensitive to detecting the growth of stenosis.

The conclusion is that Vasc‑Alert is more sensitive to change in stenosis growth than Transonic. It also suggests that the performance of Transonic might be improved with more frequent measurements than once a month.

An analysis of Transonic and Vasc‑Alert compared Vasc‑Alert and Transonic results for the same patient population.

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This analysis was internally derived from data provided by a dialysis center, which used both the Vasc‑Alert and Transonic devices for a year. While this analysis does not have the same controls as a study, it does support the following conclusions:

• Vasc‑Alert identifies more patients with issues, (74% vs. 52%)
• Vasc‑Alert identifies patients with issues earlier, (74% vs. 18%)
• When Vasc‑Alert alerts earlier, it does so with a longer lead-time. (38 vs. 26 days)

A Physiological Basis for Testing More than Once a Month

One of the reasons that Vasc‑Alert may be more sensitive to changes in stenosis is that it tests the access with each session rather than once a month. A published paper by Dr. William Paulson suggests that there is a physical basis for the need for more frequent testing The paper looks at the relative diameters of the artery supplying the access and draining vein and their influence on the use of flow-based technology to detect stenosis.
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His findings:

• For patients with very low artery to vein diameter ratios, adequate flow is maintained while stenosis is growing until it reaches a critical point and then it drops very quickly, as shown in the graph. A greater than 70+% stenosis goes undetected because the reduction in access flow is not greater than 25%.
• This helps to explain why “monthly measurements often fail to warn of thrombosis”.
• The study concludes that flow measurements should be done “at least weekly” in order to catch stenosis that is progressing at a constant rate.

Most centers using flow-based technologies test the access once a month. Vasc‑Alert tests the access with every session.

Implication:
If a center compares Vasc‑Alert results to the tests derived using flow-based methods, it is likely that Vasc‑Alert will report potential issues for certain patients before the results from a flow based technology identify that a patient is at risk for clotting. If the center does not send patients for intervention because the flow-based technology does not indicate an issue, the impression that would be developed will be that Vasc‑Alert is generating a lot of false positives because the flow-based system says there is adequate blood flow.

Operational Considerations of Both Methods: