(Attachment: catheter-vessel charts / calucations)
This has been discussed lately and continuing to develop in practice. I am attaching a PDF that explains the math for both methods:
- Area (occupancy)
- Linear (vein-catheter ratio)
To first define terms:
Area - two dimensional ‘surface’ of a given plane. Usually measures in a unit squared. Our application will be the plane (cross section) of a vein or catheter assumed to be round. Thus, the area of a circle formula would be applicable.
Area of a Circle - A = πr2
Diameter - straight line segment that passes through the center of the circle and whose endpoints lie on the circle.
Vein-Catheter Occupancy (area method) – Area of a catheter that occupies the total area of a given vessel. The portion the vein occupied by the catheter. The answer is a percentage when multiplied by 100.
Vein-Catheter Ratio (linear method) – A comparison of two diameters (lines) of the device and the vessel. The diameter of the catheter is divided by the diameter of the vessel. The answer may be represented as a percentage when multiplied by 100.
Some important concepts to note:
The math calculations are different among methods because you are evaluating different attributes of the vessel and catheter scenarios. BUT, the clinical application will yield the exact same decision making.
Guidelines developed from one method or the other will not differ in the end use of products… The research end point has to ultimately be catheter occupancy as related to vessel free space. Clinical study results will yield what is eventually assembled and will help determine where to draw the line in the same. It doesn’t matter how you draw that line. It can be with a comparison of diameters or a measure of actual occupancy. Each method would mathematically deduct its own percentage (guideline)… that is drawing the same line in the sand.
Currently if you use the linear (diameter) (vein-catheter ratio) method, the guideline has been deducted as 45% by INS correct?
If you were to apply the Area (occupancy) method to match this guideline, it would be 20%.
See attached PDF to view charts and calculations.
So, you can see one method is no better than the other… its just two different ways to measure the same thing. Of course, they will have different numerical representations but again, are drawing the same line in the sand.