105. Proximal Catheter Occlusion Simulation Study and Design of a Shunt Tap Aspiration System

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Authors: Elsa Olson; Julian Lin, MD; Jonathan Garst, MD; Hannah Abbott; Jack Blank; Aaron Shaffer; Zac Anderson (Peoria, IL)

Introduction:

Proximal catheter occlusion is a common cause of VP shunt malfunction and the concept of partial proximal obstruction is not new.  However, the degree of obstruction in a proximal catheter that ultimately leads to shunt malfunction is unknown.

Methods:

We developed a test bench to simulate proximal catheter occlusion with two hydrostatic reservoirs connected by a VP shunt catheter system.  The Centurion Compass device was used to measure pressure across the valve digitally. Wires of varying diameter (equaling different occlusion percentages) were inserted into the catheter’s proximal end to simulate obstruction.

Results:

As a general trend, pressure reading on the device decreases as occlusion increases. At higher levels of occlusion (> 45%), the blockage begins to significantly impede the flow through the catheter and the pressure drops at a faster rate compared to lower occlusion percentages. The pressure reading converges quickly to 0 with increasing blockage after about 70%. The Centurion Compass is able to detect large changes in pressure as evidenced by the major differences in pressure readings between no occlusion, 45%, and 83.94%. Even though the shunt will not function at 83.94% occlusion, it can be tapped at a higher negative aspiration pressure, 187-199 mmHg. In order to determine the threshold for occlusion beyond which fluid cannot be withdrawn, we tested five levels of occlusion (0%, 33%, 63%, 83.95%, and 100%) at various aspiration pressures and determined that fluid can still be produced with 0%-83.95% occlusion, but no fluid could be produced at 100% occlusion. 

Conclusion:

We developed a model of proximal shunt obstruction and found the shunt will work at 50% occlusion but unlikely at 80%. Pressure measured at reservoir is accurate and correlates with ventricular pressure up to 60% occlusion. With partial occlusion up to 70%, ventricular pressure will dictate shunt function.

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