SHUNT SYSTEM

It is used to prevent the siphon effect that may occur when the peritoneal catheter changes from horizontal to vertical position during the drainage or shunting of the cerebrospinal fluid (CSF).

 

 

 

 

 

 

 

Figure 1. ProGAV mechanism

MIETHKE proGAV is a position dependent valve. The opening pressure of the valve changes automatically according to the patient's body position. When a proGAV is to be administered, a working pressure is determined for the patient's horizontal position and a different working pressure for the vertical position.

 

 

Horizontal position (at the time of hospitalization)

 

 

 

 

 

 

 

 

 

Figure-2. Gravitational unit

The adjustable unit valve part determines the operating pressure in the horizontal position of the body. In this position, the gravitational unit has no effect on the working pressure. Between 0 and 20 cmH2O (21 steps), the value suitable for the patient is determined and the working pressure of the valve is adjusted. When the patient is in a horizontal position, the gravitational unit is always on, there is no obstacle to the CSF flow (Figure 2). Therefore, the working pressure of the valve is predominantly determined by the adjustable unit. The functions of the adjustable unit are shown in Figures 3 and 4.

 

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 Figure-3. Adjustable unit - valve closed
 

 

 

 

Figure-4. Adjustable unit -valve open

In Figure 3, the ball in the conical section keeps the valve closed and there is no drainage. In Figure 4, the adjustable unit is open. The patient's intraventricular pressure (IVP) increased and this pressure overcame the force applied by the spring holding the valve in the closed position. The closing ball is slightly pushed out of the conical part and the gap in between allows drainage.

 

Vertical position (standing)

  As soon as the patient moves to a vertical position, the garavitational unit turns off. Therefore, proGAV operating pressure switches to high level and CSF drainage stops (Figure 5). Drainage resumes when the sum of intraventricular pressure and hydrostatic pressure exceeds the proGAV second stage working pressure (Figure 6). The proGAV working pressure in the vertical position is equal to the sum of the adjustable unit and the gravitational unit operating pressures.