title: Ureteric access with flexible ureteroscopes: effect of the size of the ureteroscope.
abstract: OBJECTIVE
  To determine the optimum size of a flexible ureteroscope (FU) to minimize the need for ureteric dilatation.
  
  
  METHODS
  FUs from several different manufacturers and with different shaft diameters were used for ureteroscopy in adults. An initial attempt was made to pass one of the larger diameter FUs; if this was unsuccessful, the smaller 7.5 F FU was used. The results were reviewed retrospectively.
  
  
  RESULTS
  Flexible ureteroscopy was used in 115 consecutive patients at two different institutions. The ability to pass the FUs with no formal dilatation was directly related to the FU diameter. The rate of failing to pass with no formal dilatation was 37% for the 9.0 F, 8.5% for the 8.6 F, 5% for the 8.4 F and 0.9% for the 7.4 F ureteroscope.
  
  
  CONCLUSIONS
  Although other factors influence the overall effectiveness of the FU, the ability to pass FUs is directly related to their outer diameter. When only the ease of introduction is considered, the ideal ureteroscope outer diameter is 7.4 F.
authors.affiliation: Division of Urology and Renal Transplantation, Oregon Health Sciences University, Portland, OR 97201-3098, USA.
authors.forename: R Guy
authors.initials: RG
authors.lastname: Hudson
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Conlin
authors.forename: Demetrius H
authors.initials: DH
authors.lastname: Bagley
mesh_terms: D000328:Adult; D004106:Dilatation / Q000379:methods; D004867:Equipment Design; D005260:Female; D006801:Humans; D008297:Male; D012189:Retrospective Studies; D014514:Ureteral Calculi / Q000175:diagnosis*; D020709:Ureteroscopes