MIETHKE proSA Manuel Du Patient page 8

| PATIENT MANUAL
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The patient should avoid knocks or pressure on the
valve and catheters. The valve has been designed
to be resistant against magnetic fields.
PHYSICS BACKGROUND
The following chapter describes the pressure con-
ditions relevant for hydrocephalus drainage. The
ventricle pressure and the pressure in the abdo-
minal cavity are represented by water levels. In a
healthy human, the ventricular pressure (water level
in the ventricle container) is positive (slightly above
0) in the horizontal position and negative (slightly
below 0) in the upright (vertical) position (see fig. 4)
1 ventricle container
2 ventricles
0
1 2
Abb. 4a: Ventricle pressure in a healthy human in
horizontal position
0
1
Fig. 4b: Ventricle pressure in a healthy
human in vertical position
In hydrocephalus patients, the ventricular pressure
is always increased (water level in the ventricle con-
tainer far above 0) regardless of the body position.
The ventricles are expanded (see fig. 5).
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1 ventricle container
2 ventricles
0
1 2
Fig. 5a: Ventricle pressure in a hydrocephalus patient in
horizontal position
0
1
Fig. 5b: Ventricle pressure in a hydrocephalus patient in
vertical position
Now there is an urgent need to lower the intracra-
nial pressure und keep it within normal limits, regar-
dless of the body position. Finally, excessive cere-
brospinal fluid is drained into the abdominal cavity.
Fig. 6 shows the effects on the intracranial pres-
sure when a tube is implanted, although there has
been no valve integrated in the drainage system
yet. For simplicity, the abdominal pressure as well
as the ventricles can be regarded as open vessels,
which are now connected by a tube. As long as
the patient is lying down (head and abdomen at
the same height) and no valve is integrated in the
drainage system, both water levels are at the same
height, too: It is a system of communicating ves-
sels. In a simplified picture, the abdomen can be
regarded as an overflow vessel. Even if more fluid
is filled into the ventricle container, the water level in
it will remain at the same height, because the fluid
is instantly drained into the abdomen.
When the patient stands up, the ventricles are at a
significantly higher level than the abdomen. In this
case, the fluid is drained through the tube until both
water levels are at the same height. This means,
however, that the ventricle container is emptied
completely. Since the ventricles do not have rigid
walls, this drainage leads to a contraction of the
ventricles.
1 ventricle container
2 ventricle
3 drainage tube
4 abdominal cavity
5 abdominal container
0
a) 1 2 3 4 5
1
0
5
b)
Fig. 6: Ventricle drainage without a valve
a) horizontal, b) vertical
A conventional valve integrated into the drainage
system causes a rise of the water level in the ventri-
cle container, by exactly the opening pressure of
the valve. Now, the two containers "communicate"
only when the valve is open. When the patient
stands up, cerebrospinal fluid is drained off until
the height difference between the two containers
for the horizontal position is reached.
However, the opening pressure of the valve, which
was adjusted for the horizontal position, is consi-
derably lower than the pressure corresponding to
the height difference between the ventricles and
the abdomen. Hence, the ventricles will still be
drained empty, resulting in the above mentioned
problems (Fig. 7).
PATIENT MANUAL |
x
a)
x
b)
3
Fig. 7: Ventricle drainage with conventional valve
a) horizontal, b) vertical, x = opening pressure
4
The simplified diagram clearly demonstrates how
crucial it is that a valve is implanted whose ope-
ning pressure is considerably higher for standing
(and sitting) position (depending on the distance
between the brain and stomach) than for horizon-
tal position. If a simple or adjustable valve is no-
netheless implanted that only functions adequately
in horizontal position, the shunt system must be
equipped with a supplementary valve for standing
(and sitting) positions.
The proSA is such a supplementary valve. It func-
tions exclusively when the patient is standing (or
sitting) and, in combination with the differential
pressure valve, ensures that the intracranial pres-
sure will be exactly what the patient needs in every
body position. The problems and complications
caused by undesirably high levels of drainage are
thus avoided (Fig. 8).
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