title: The enigma of underdrainage in shunting with hydrostatic valves and possible solutions.
abstract: OBJECTIVE
  Hydrostatic devices have considerable advantages compared to "conventional" differential-pressure-valves concerning overdrainage, but are thought to imply a tendency to underdrain or to clog. The aim of this study was to evaluate the ability of the hydrostatic gravitational Dual-Switch-Valve (DSV) to minimize overdrainage-related complications without increasing the danger of underdrainage.
  
  
  RESULTS
  In a series of 202 adult patients with different etiologies treated with a ventriculo-peritoneal shunt including the hydrostatic Dual-Switch-valve (DSV), 21 cases were suspected of suffering from underdrainage. Using a new algorithm we were able to differentiate obstruction in 6 patients from functional underdrainage in 15 cases, thus we saw an indication to reimplant a DSV with a lower opening pressure in the latter.
  
  
  CONCLUSIONS
  The reasons for functional underdrainage were multifold in our series, especially the intraperitoneal pressure is still a "black box". Despite the ability of the DSV to avoid clogging and to minimize overdrainage by its high-pressure-chamber, it remains difficult to determine the optimal opening pressure of the low-pressure-chamber of the DSV for ideal clinical improvement. Therefore a new hydrostatic gravitational "programmable" valve (proGAV), entitled on avoiding the disadvantages of other adjustable devices, has been developed and implanted in 16 patients with promising results.
authors.affiliation: Neurosurgical Department, Charité, Humboldt-University, Berlin, Germany. christian.sprung@charite.de
authors.forename: C
authors.initials: C
authors.lastname: Sprung
authors.forename: C
authors.initials: C
authors.lastname: Miethke
authors.forename: H-G
authors.initials: HG
authors.lastname: Schlosser
authors.forename: M
authors.initials: M
authors.lastname: Brock
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002557:Cerebrospinal Fluid Shunts / Q000295:instrumentation* / Q000379:methods; D019544:Equipment Failure Analysis; D005260:Female; D006801:Humans; D006849:Hydrocephalus / Q000175:diagnosis* / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011475:Prosthesis Failure; D017755:Prosthesis Fitting / Q000379:methods; D016896:Treatment Outcome