title: Intra-abdominal pressure: the neglected variable in selecting the ventriculoperitoneal shunt for treating hydrocephalus.
abstract: OBJECTIVE
  In the selection of a ventriculoperitoneal cerebrospinal fluid shunt, the intra-abdominal pressure (IAP) is traditionally neglected as a result of the idea that its value is close to 0 mmHg. Our aim was to explore the relationship between body mass index (BMI) and IAP with the goal of providing clinically relevant data that could help neurosurgeons to estimate IAP and select the appropriate shunt for patients with hydrocephalus and especially those with normal-pressure hydrocephalus syndrome.
  
  
  METHODS
  Sixty patients requiring the placement of a ventriculoperitoneal shunt were included in the study. We determined weight, BMI, and IAP. IAP was measured through an intraperitoneal catheter during the shunt surgery. To determine whether a linear relationship existed between quantitative variables, linear regression analysis was used.
  
  
  RESULTS
  BMI was 28.1 +/- 4.8 kg/m2. Eighteen patients (30%) had normal weight, 21 (35%) were moderately overweight, and 21 (35%) were obese. IAP was related to patient BMI. A significant positive linear correlation was identified between BMI and IAP (r = 0.52; P = 0.018) with a slope of 0.31 (P < 0.001) and an intercept of -5.5.
  
  
  CONCLUSIONS
  In our study, we determined that IAP had a strong positive linear relationship with BMI. This correlation was independent of sex. An IAP of 0 mmHg can, therefore, only be assumed for patients with a normal BMI who are recumbent. In obese or overweight patients, neurosurgeons should take IAP into account when selecting both the most adequate differential pressure valve to be implanted and in which distal cavity to place the distal catheter to avoid shunt underdrainage induced by high IAP.
authors.affiliation: Department of Neurosurgery, Neurotraumatology, Vall d'Hebron University Hospital, Autonomous University of Barcelona, Barcelona, Spain. sahuquillo@neurotrauma.net
authors.forename: Juan
authors.initials: J
authors.lastname: Sahuquillo
authors.forename: Fuat
authors.initials: F
authors.lastname: Arikan
authors.forename: Maria A
authors.initials: MA
authors.lastname: Poca
authors.forename: Montserrat
authors.initials: M
authors.lastname: Noguer
authors.forename: Francisco
authors.initials: F
authors.lastname: Martinez-Ricarte
mesh_terms: D000005:Abdomen / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D005260:Female; D006801:Humans; D006849:Hydrocephalus / Q000601:surgery*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D011312:Pressure; D014057:Tomography, X-Ray Computed; D017287:Ventriculoperitoneal Shunt / Q000379:methods*