miethke Shuntassistant 2.0 Patientenhandbuch Seite 22

SA 2.0 operating principle
A proper understanding of the operating principle of SHUNTASSISTANT 2.0
(SA 2.0) requires a brief look at the physical framework conditions that
such drainage involves: creating a link between these two systems - ventri-
cle and abdominal cavity - might allow the CSF to drain without control,
particularly when the patient stands upright, thus transporting too much of
the fluid from the ventricles to the abdominal cavity. This is called overdrai-
nage and must be prevented by all means. However, is it is entirely normal
for a mobile human being to change position frequently: to stand up, walk,
sit down or lie down. All this results in continuous physical changes in the
drainage system.
In order to achieve a controlled drainage of the cerebrospinal fluid, a valve
such as SA 2.0 is implanted together with the tube system. This combi-
nation of a tube system and a valve is known as a shunt system. Ideally, a
valve such as SA 2.0 ensures that CSF is only drained off when the pres-
sure inside the ventricles becomes too high. To that end, the valves have
pre-set or settable opening pressures, i.e. a valve opens once a predefined
intracranial pressure has been reached, thus preventing over- or underdrai-
nage. However, the optimum opening pressure in a lying position is not the
same as in an upright one. This is the consequence of the physical laws of
gravity (gravitation).
Physical background
Two interlinked fluid-filled vessels that are - as in a lying person - horizontal
to each other aim to balance each other. A conventional differential pres-
sure valve with a low opening pressure requires a second component with
a higher opening pressure in the upright position, as otherwise too much
cerebrospinal fluid can drain in an upright body position. This could lead to
excessive drainage and therefore to serious complications.
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// SA 2.0 PATIENT MANUAL