title: An investigation into the clinical impacts of lowering shunt opening pressure in idiopathic normal pressure hydrocephalus: A case series.
abstract: BACKGROUND
  Idiopathic normal pressure hydrocephalus (iNPH) is a shunt- reversible syndrome of the elderly. Shunt management is aimed at achieving a balance between clinical improvement and the complications associated with overdrainage. Although clinical improvement occurs at low pressure, these benefits may be negated by the increase in complication rates observed at lower pressures. The addition of gravity-switch devices has been shown to reduce over drainage problems even at a low valve pressure setting. At our centre the Miethke proGAV is used and commonly lowered below 5 cmH2O to gain further clinical improvement.
  
  
  OBJECTIVE
  To determine whether lowering the opening pressure to below 5cmH2O using the proGAV valve in iNPH patients results in a) improved clinical features; and b) no significant increase in complication rates.
  
  
  METHODS
  A retrospective case series of iNPH patients was undertaken with 24 patients who had the proGAV shunt system inserted with an initial opening pressure of 5cmH2O. Exclusion criteria were secondary NPH, shunt system other than proGAV inserted, no valve adjustment to below 5cmH2O and inadequate follow-up. Outcome measures were clinical improvement (gait, cognition and urinary continence) and complications (subdural haematoma, low-pressure symptoms and valve damage).
  
  
  RESULTS
  Patients underwent a total of 29 adjustments to below 5cmH2O. The mean valve opening pressure after the first adjustment was 2.5cmH2O and the mean opening pressure after the second adjustment was 1cmH2O. Overall, outcome after adjustment included 26% no change, 48% improvement and 26% deterioration clinically. One patient (4%) suffered traumatic subdural haematoma that resolved with increasing valve pressure to 20cmH2O. There was no valve damage or low-pressure symptoms after adjustment.
  
  
  CONCLUSIONS
  This study found that lowering the opening pressure of the proGAV shunt system to below 5cmH2O results in clinical improvement and does not significantly increase the complication rate in iNPH patients.
authors.affiliation: a Victor Horsley Department of Neurosurgery , National Hospital for Neurology and Neurosurgery , Queen Square, London , UK.
authors.forename: David N
authors.initials: DN
authors.lastname: Malem
authors.affiliation: a Victor Horsley Department of Neurosurgery , National Hospital for Neurology and Neurosurgery , Queen Square, London , UK.
authors.forename: James D
authors.initials: JD
authors.lastname: Shand Smith
authors.affiliation: a Victor Horsley Department of Neurosurgery , National Hospital for Neurology and Neurosurgery , Queen Square, London , UK.
authors.forename: Ahmed K
authors.initials: AK
authors.lastname: Toma
authors.affiliation: a Victor Horsley Department of Neurosurgery , National Hospital for Neurology and Neurosurgery , Queen Square, London , UK.
authors.forename: Huma
authors.initials: H
authors.lastname: Sethi
authors.affiliation: a Victor Horsley Department of Neurosurgery , National Hospital for Neurology and Neurosurgery , Queen Square, London , UK.
authors.forename: Neil D
authors.initials: ND
authors.lastname: Kitchen
authors.affiliation: a Victor Horsley Department of Neurosurgery , National Hospital for Neurology and Neurosurgery , Queen Square, London , UK.
authors.forename: Laurence D
authors.initials: LD
authors.lastname: Watkins
keywords: normal pressure hydrocephalus; overdrainage symptoms; proGAV shunt; subdural haematoma; ventriculoperitoneal shunt