Simulation of proximal catheter occlusion and design of a shunt tap aspiration system

Abstract

Purpose

Total and partial proximal catheter occlusions are well-known complications of ventriculoperitoneal shunts (VPS). When this occurs, surgeons often attempt to perform a shunt tap. However, the degree of obstruction in a proximal catheter that ultimately leads to shunt malfunction is unknown.

Methods

We developed a benchtop model to simulate proximal catheter occlusion with two hydrostatic reservoirs connected by a VPS catheter system. The Centurion compass device was used to measure pressure across the valve digitally. Wires of varying diameters (equalling different occlusion percentages) were inserted into the catheter’s proximal end to stimulate obstruction. A mock shunt tap aspiration was then performed by incorporating a pressure transducer.

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 with 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 84%. The shunt will not function at 84%. In order to determine the threshold for occlusion beyond which fluid cannot be withdrawn, we tested five levels of occlusion (0%, 33%, 63%, 84%, and 100%) at various aspiration pressures and determined that fluid can still be produced with 0–84% occlusion, but no fluid could be produced at 100% occlusion.

Conclusions

We developed a model of proximal shunt obstruction and found that cerebrospinal fluid (CSF) flow through a VPS is unaffected up to 33% occlusion, begins to become impaired at 45% occlusion, and is miniscule at 84% occlusion. Shunt aspiration was not possible at 84% occlusion. Pressure measured at the reservoir is accurate and correlates with intracranial pressure (ICP) up to approximately 60% proximal occlusion. With partial occlusion up to 70%, ventricular pressure will dictate shunt function.

Appendices

Appendix 1. Formulating an equation

The following equations demonstrate the mathematical logic and organization used to define the relationship between ventricle pressure, compass pressure, and occlusion:

$$ W=\left[{w}_0\ {w}_1\ {w}_2\ {w}_3\ {w}_4\ \right]={\left(\sum \limits_{i=1}^{36}\left[1\ {v}_i\ {v_i}^2\ {s}_i\ {s_i}^2\ \right]\left[1\ {v}_i\ {v_i}^2\ {s}_i\ {s_i}^2\ \right]\right)}^{-1}\sum \limits_{i=1}^n\left[1\ {v}_i\ {v_i}^2\ {s}_i\ {s}^2\ \right]{b}_i $$

(5)

$$ B\left(v,s\right)={w}_0+{w}_1v+{w}_2{v}^2{w}_3s+{w}_4{s}^2 $$

(6)

$$ J=\sum \limits_{i=1}^{36}{\left(B\left({v}_i,{s}_i\right)-{b}_i\right)}^2 $$

(7)

where v, s, and b are all 1 × 36 matrices consisting of ventricle pressures for v, extraction pressures for s, and percent occlusion for b. Below is the MATLAB code used to calculate the function and J with x=v, y=s, z=b, and f(x,y)=B(v,s).

MATLAB code for the function:

Where J was found to be 1.0775e+04

Appendix 2. Omega pressure sensor

The OMEGA pressure sensor is a gage pressure sensor for pressure applications below 1 psi. A 4-pin connector was installed on 4 pins and connected to a voltage supply as well as a digital multimeter. The digital multimeter displayed the output voltage of the pressure sensor which was manipulated into pressure values via the manufacturer curve to verify the theory of hydrostatic pressure. This verification was deemed necessary as the brain ventricle pressure represented by the height of water in the first column needed to be accurate and carefully monitored to verify the data collected in this study (“PC Mountable Wet/Wet Differential Pressure Sensor | Omega Engineering US,” n.d.).