gms | German Medical Science

Objective: Since 1949 more than 300 hydrocephalus valves were designed, 220 were implanted in the course of time, and 170 are on the market. Unfortunately the nomenclature is a chaos of 1. inventor/company or 2. fantasy terms (e.g.“Diamond”), which contain no real information. Other terms contain minimal data either on 3. valve body (“burr hole”), 4. shunt assembly (“Unishunt”), 5. special age (“neonatal”), 6. implantation sites (“Lumbar”), 7. number of pressure ranges (Sophy SU3/8), 8. pressure-flow-curves (“Sigma”) or 9. technical details (“slit”). 10. Some use advertizing terms “programmable”, which suggests computer technology, but contain in reality simple adjustable springs only. 11. There are physically incorrect terms: E.g. the “flow-controlled” Orbis-Sigma is controlled by pressure, not by flow. 12. The basic hydraulic properties are not standardized: MEDIUM often overlap LOW/HIGH. It is not only a problem of words and terms: Clinical evaluations as well controlled studies contain often inconsistent subgroups, which disturb the significance or the reliability of studies.

Method: We analyzed the hydraulics and designs of all valves and propose a nomenclatur centered on hydraulics in vertical/horizontal position. We try to look on the probable future.

Results: The hydraulics require data on 1. the pressure curves (L-M-H or detailled curves) and 2. the variability. Conventional valves show prefixed curves (2.1), more recent designs are manually adjustable (2.2), show a pressure-dependent negative feedback-regulation (Orbis-Sigma, Diamond, SiphonGuard, 2.3) or are controlled by gravity, ergo the body position. The acting weight can be either the water column in the catheter distal of a collaps-switch (antisiphons 2.4), implemented balls (gravitational valves, 2.5) or electronic sensors. An increasing number of new designs combine two principles: adjustment + ASD (Strata), or gravitational (ProGAV). Subcriteria are details (ball, slit, adjustment, “brakes”), materials, body design and shunt assembly. Electronic “smart” shunts concepted since 3 decades failed due to luck of long-term-reliable ICP-sensors and unsolved energy problems.

Conclusions: More than 300 valves, of them 220 implanted and 170 on the market, let to an increasing confusion, handling errors and fail-classifications in studies. 2 hydraulic and 4 supplementary specifications allow an universal and transparent classification of all shunt systems. Electronic shunts need probably decades for realization.