title: Permeability of the silicone membrane in laparoscopic adjustable gastric bands has important clinical implications.
abstract: BACKGROUND
  The single most important attribute of the laparoscopic adjustable gastric band (LAGB) is its adjustability. Having the correct volume of fluid within the band is crucial for optimal performance. We observe a small reduction of the satiety-promoting effect with time. The characteristics and clinical relevance of volume change have not been adequately investigated.
  
  
  METHODS
  One observer measured the saline volume within the 10-cm Lap-Band in 118 consecutive patients who fulfilled the entry criteria. The same observer had performed and recorded the previous adjustment. Initial volume, final volume and time between observations provide the data for analysis. In addition, a range of adjustable gastric bands currently available were bench-tested to assess broad applicability of findings.
  
  
  RESULTS
  The difference between observations varied from 0.0 ml to -1.0 ml, median of -0.1 interquartile range (IQR) 0.0-0.2 ml. Two factors were associated with volume change: time in days between the observations (r = -0.55, P<0.001) and the initial volume within the band system (r = -0.50, P<0.001). These two independent factors accounted for a significant proportion of the variance observed (Cox and Snell R2 = 0.45, P<0.001). Replacement of any discrepancy appears to maintain effectiveness. All six bands showed similar saline loss when bench-tested.
  
  
  CONCLUSIONS
  Adjustable gastric bands are semipermeable, leading to a small reduction in saline volume with time. Patients should be informed of this effect, attend for regular follow-up visits and seek help if the band's effectiveness appears reduced. We recommend that the volume present should be checked and readjusted at least every 6 months.
authors.affiliation: Australian Centre for Obesity Research and Education, Monash Medical School, The Alfred Hospital, Melbourne, Australia. john.dixon@med.monash.edu.au
authors.forename: John B
authors.initials: JB
authors.lastname: Dixon
authors.forename: Paul E
authors.initials: PE
authors.lastname: O'Brien
mesh_terms: D019544:Equipment Failure Analysis; D015391:Gastroplasty / Q000295:instrumentation*; D006801:Humans; D010535:Laparoscopy; D016015:Logistic Models; D009765:Obesity / Q000601:surgery*; D010539:Permeability; D012828:Silicones
chemical_list: D012828:Silicones