Function Of The Valve; Selecting The Appropriate Valve - miethke GAV Gebrauchsanweisung

| INSTRUCTIONS FOR USE
GB

FUNCTION OF THE VALVE

The operating principle of the GAV is illustrated
in fig. 3 and fig. 4.
Fig. 3 a shows the GAV in a horizontal position.
The ball-cone unit is closed and the drainage is
blocked. In fig. 3 b, the GAV is shown when it
is open. The increased IVP of the patient over-
comes the spring force, which otherwise would
keep the ball-cone unit closed. The closing ball
is pushed away from the cone seal and a gap
opens for fluid drainage. The gravitational unit is
always open in the horizontal position and does
not present any resistance to the drainage flow.
ball-cone unit
a)
b)
Fig. 3: GAV in horizontal position
a) closed b) open
As soon as the patient raises to a vertical po-
sition, the gravitational unit closes and the drai-
nage is interrupted (fig. 4 a). In this position, the
sum of the IVP and the hydrostatic pressure
surpasses the spring force of the ball-cone unit.
Therefore this valve is open now. But only when
the sum of the IVP and the hydrostatic pressure
exceeds the gravitational force on the tantalum
ball in the gravitational unit, the drainage path is
open again (fig. 4 b).
a) b)
Fig. 4: GAV in a vertical position
a) closed b) open
16
gravitational unit

SELECTING THE APPROPRIATE VALVE

The GAV operates in different modes depen-
ding on the physical position of the patient. It
features two different opening pressures, one
for the patient in a horizontal position and one
for a vertical position.
Percutaneous readjustments of the valve ope-
ning pressure become unnecessary through
this design, as a higher opening pressure in the
vertical position counteracts any unintentional
overdraining, while the lower opening pressure
required for when the patient is lying down rules
out any underdrainage.
Horizontal position:
For the horizontal position, two different ope-
ning pressure settings are available (5 and 10
cmH O). The pressure setting should be cho-
2
sen according to the clinical picture (normal-
pressure hydrocephalus, hypertonic hydroce-
phalus).
Vertical position:
The opening pressure for the vertical position
depends on the body length of the patient (hy-
drostatics). We recommend to select a pres-
sure setting guided by the height difference
between the third ventricle and the diaphragm.
(see recommendation of pressure settings at
www.miethke.com)
GAV