Elevated intra-access pressure (IAP) is a marker for stenosis. As an occlusion develops, it restricts the flow of blood, which increases the pressure at the tip of the needles. The venous needle has to push harder while the arterial pump has to pull more to maintain blood flow.
To derive the IAP, Vasc-Alert takes the venous pressure recorded in the treatment data and subtracts the back-pressures due to the bloodlines and needles. It also compensates for hematocrit and several other factors to calculate the pressure at the tip of the needle. This calculated IAP pressure is then divided by the MAP to normalize the result to changes in the patient’s blood pressure, (venous access pressure ratio or VAPR).
This ratio is compared to a threshold that corresponds to approximately 50% to 60% occlusion, which is the minimum occlusion required for an intervention. If pressures are above the threshold for three consecutive treatments, the system automatically issues an alert to staff indicating that the patient may be at risk of an access complication (red lines in example). Every week, new reports are provided to clinical staff because access issues can develop quickly.
Increasing pressure equals increasing stenosis
This graph depicts an increasing trend in VAPR over the past 6-months. The higher the pressures the higher the risk for thrombosis. When the patient was referred and an angioplasty was performed (red arrows), the pressures were decreased.
The first angioplasty was 95% occluded.
The second was 75%.
New AV Fistula that was Lost
As a new fistula matures, VAPR pressures should decrease as the access expands. In this example, the pressures are increasing indicating growing risk. Unfortunately, this patient was not referred in time and had to revert to a catheter as noted by the top yellow bar.
New AV Fistula that is Doing Well
Here is an example of a new fistula that is maturing well as indicated by the drop in pressures.