title: Outflow resistance of the Baerveldt glaucoma drainage implant and modifications for early postoperative intraocular pressure control.
abstract: OBJECTIVE
  To determine outflow resistance of the Baerveldt glaucoma implant using different tube configurations.
  
  
  METHODS
  Outflow resistance of 6 tube configurations (C1- C6) of Baerveldt implants was measured under conditions of constant pressure perfusion. Pressures ranged from 2 to 55 mm Hg. Venting slits were created using a 7-0 Vicryl, spatulated suture-needle. Seton tubes were occluded by threading a retrograde suture approximately 1.5 cm into the lumen.
  
  
  RESULTS
  At pressures between 2 and 55 mm Hg, mean outflow resistance of the normally configured seton (ie, open tube; C1) was 0.41 (+/- 0.6) mm Hg/microL/min. Resistance was unchanged (mean 0.41 (+/- 0.4) mm Hg/microL/min) by the addition of 4 venting slits (C2) to the seton tube. Occlusion of the open seton tube with a 3-0 Supramid suture (C3) significantly increased (P < 0.001) mean outflow resistance to 14.99 (+/- 0.6) mm Hg/microL/min. Occlusion of the tube with a 4-0 Supramid suture (C4) significantly increased (P < 0.001) mean outflow resistance to 1.09 (+/- 0.5) mm Hg/microL/min. In implants where tubes were occluded with a 3-0 Supramid suture, the addition of venting slits (C5) significantly decreased (P = 0.038) mean outflow resistance to 8.98 (+/- 0.4) mm Hg/microL/min. In tubes occluded with a 4-0 Supramid suture, the addition of venting slits (C6) decreased mean outflow resistance to 0.98 (+/- 0.6) mm Hg/microL/min.
  
  
  CONCLUSIONS
  Although these results cannot be directly correlated to the clinical setting, they do show that outflow resistance can be modified at the time of surgery by changing tube configuration of the Baerveldt glaucoma implant. Configuration C5 (3-0 Supramid with venting slits) closely approximates the outflow rate in the normal intraocular pressure range.
authors.affiliation: Hewitt Laboratory of the Ola B. Williams Glaucoma Center, Department of Ophthalmology, Medical University of South Carolina, Charleston, South Carolina, USA.
authors.forename: R Reid
authors.initials: RR
authors.lastname: Breckenridge
authors.forename: Luanna R
authors.initials: LR
authors.lastname: Bartholomew
authors.forename: Craig E
authors.initials: CE
authors.lastname: Crosson
authors.forename: Alexander R
authors.initials: AR
authors.lastname: Kent
mesh_terms: D004322:Drainage / Q000295:instrumentation*; D004867:Equipment Design; D005901:Glaucoma / Q000503:physiopathology* / Q000601:surgery*; D006801:Humans; D007429:Intraocular Pressure; D011184:Postoperative Period; D011312:Pressure; D019736:Prostheses and Implants; D012016:Reference Values; D012212:Rheology