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Hydrocephalus FAQ
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We have created this section on hydrocephalus frequently asked questions (FAQ) to help answer some commonly asked questions regarding CNS (central nervous system) shunts. Over time, we will add more responses and hopefully address many of the shunt issues and questions today. For the most COMPLETE hydrocephalus information, see our main section on hydrocephalus (linked below). Visit: Main Section on Hydrocephalus Information and Advocacy Visit: Special 2008 Hydrocephalus Study: Shunt Selection Model Q: What's are the difference between the three available programmable shunts? The primary differences between the
available programmable shunts
are in the number of available
settings. The Codman Medos valve can be more finely tuned,
as it has 10mm H2O increments to
select from ranging 30 to 200, for a
total of 18 settings. The Medtronic Strata only
has 5 settings,
where it's lowest setting of
0.5 is equivalent to about 50 mmH2O
or so
on the Codman.
In comparing the Medtronic to the Codman, the
cut-off opening pressure on the low end can be a problem for some patients requiring
a very low setting. The Sophysa programmable
comes in four different models ranging from 10 to 140 mm H2O, 30 to 200 mm H20,
50 to 300 mm H2O, and 80 to 400 mm H2O. Each has eight pressure selections to
choose from. The SM8 model, with 30 to 200 mm H20, is their standard model. Both come
with different types of anti-siphon devices integrated within the valve. The
Medos uses the Siphon Guard, whereas the Strata uses the SCD. However, the
Strata is not available w/o SCD, whereas the Medos comes with or without its
siphon guard system. It seems the majority of adults today require siphon
control, perhaps a bit fewer in NPH, and it can cause problems for some.
Codman's siphon guard is pretty simple and stable, though is reported to
experience more obstructions due to its fine flow path. The Medtronic SCD system
is very much dependent on the vertical location on the head where the valve is
placed, and is recommended to be placed at “zero point,” or near the level
of the top of the ear (middle of ventricles). Near the top of the head, the SCD
does not flow as much when sitting or standing, and place it too low on the head
and it won't retard overdrainage much at all. The nsg can “partly” offset
the SCD’s upright flow control by raising or lowering the Strata setting. But
at the top or bottom of the pressure selections, it's possible you will NEVER be
able to get the right setting. The Codman Siphon Guard is unaffected by these
issues, and it can pretty much work well on any patient. Still, both ADD
additional flow resistance, and cause an effective higher opening pressure in
these shunts. As both are
programmable, their settings CAN be accidentally changed by magnetic fields
around the home. The only way to know which setting these two programmable
shunts are set to is with a by skull x-ray. Of interest, the setting on the
newer Sophysa Polaris programmable shunt can be read via the programming meter
in the nsgs office. The Polaris also has a LOCKING mechanism, and is the least
affected by magnetic fields. But it has does NOT come with any siphon control
system. Nsgs often will attach an SCD or Shunt Assistant (Mfr Meithke) in line
to control overdrainage when upright. There are
many mixed reports on how prevalent it is for programmable shunts to
accidentally loose their setting from magnetic fields around the home and such.
You can ask your nsg as to his/her experiences and views. Patient forums are
filled with stories telling that this is happening quite often. My own
experiences and study of the issue suggests it is happening more than is being
reported, primarily because the only way to document when Medtronic and Codman
programmable shunt looses its setting is via a skull x-ray. And the use of the
x-ray procedure is more INTENDED for confirming the shunt’s setting after
being programmed, rather than DOCUMENTING if and when its setting might have
been changed. My Codman
Medos shunt had to be replaced after only 9 months as it was found to be
frequently loosing its setting, and towards the end nearly 2-3 times a week. I
was revised to the Orbis Sigma shunt (mfr Integra) that is not programmable, but
termed "auto adjusting." I am more pleased with this OSV-2 and I don't
have to fuss with the settings issue. Overall, I
favor the Codman Medos over the Medtronic Strata. If the Strata were more
carefully chosen and specifically placed on a user’s head, it could perhaps be
more reliable than the Medos with Siphon Guard. The Siphon Guard has been
reported to be linked to shunt obstructions from debris as it has a very fine
flow pathway. If you're active and around a lot of electronic
equipment, gaming, and household devices, I’d recommend the OSV-2 Orbis Sigma
valve. If your hydrocephalus and CSF outflow requirements require a shunt valve
with more CSF outflow than the OSV-2, I'd recommend the
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