title: [Thomas' shunt for hemodialysis: dysfunction and its percutaneous treatment].
abstract: OBJECTIVE
  To assess the usefulness of percutaneous treatment of abnormalities of the venous tree in extending the survival of external Thomas shunts (TS).
  
  
  METHODS
  Twelve cases of TS were included in a hemodialysis access fistula dysfunction monitoring program and were followed for up to 48 months. The abnormalities found were treated by percutaneous transluminal angioplasty (PTA) or thrombolysis and PTA. Survival curves and the Kaplan-Meier method were used to calculate the likelihood of primary patency (P1), secondary patency (P2), and overall patency (OP).
  
  
  RESULTS
  A total of 61 interventions were performed during the period of follow-up. On 12 occasions the fistula was thrombosed; in the rest, increased venous pressure to 150 mmHg or higher was detected during dialysis. Fistulography was performed after washing the thrombosed fistulas with urokinase, and revealed one or more of the following angiographic signs: 1) a short reduction of more than 50% in lumen caliber in the femoral vein adjacent to the anastomosis, present in 52% of the cases (fig. 1); 2) imaging a "jet" of contrast material at the site of entry of the shunt into the femoral vein (fig. 2), present in 22% of the cases; and 3) a filling defect or "flap" at the same site, owing to hyperplastic tissue or piece of thrombus adhering to the intima, present in 34% of the cases (figs. 3-5). This last-mentioned finding ordinarily gave rise to a "valve" effect, whereby injection into the venous branch was feasible but aspiration from the venous branch was difficult or impossible. PTA was carried out and attained anatomical and functional success in 100% of cases. PI was 58%, 33%, 8%, and 0% at 6, 12, 24, and 36 months, respectively; P2 was 100%, 75%, 58%, and 25%; respectively, at those same times. The comparison of the PI and P2 curves was statistically significant; p < 0.001 (table 1). OP was 83%, 66%, 50% and 41% at 12, 24, 36 and 48 months. The comparison of the PI surgical and OP curves was statistically significant; p < 0.01 (table II).
  
  
  CONCLUSIONS
  Percutaneous treatment of TS dysfunction was proved to be effective in maintaining long-term patency. This type of fistula affords an alternative to tunneled central venous catheters.
authors.affiliation: Servicio de Radiodiagnóstico, Hospital Clínico San Carlos, Madrid. jgallego@hcsc.insalud.es
authors.forename: J J
authors.initials: JJ
authors.lastname: Gallego
authors.forename: E
authors.initials: E
authors.lastname: Santos
authors.forename: J V
authors.initials: JV
authors.lastname: Méndez
authors.forename: F
authors.initials: F
authors.lastname: Coronel
authors.forename: J
authors.initials: J
authors.lastname: Torrente
authors.forename: A
authors.initials: A
authors.lastname: Holguín
authors.forename: R
authors.initials: R
authors.lastname: Moreno
mesh_terms: D000328:Adult; D000368:Aged; D001166:Arteriovenous Shunt, Surgical / Q000009:adverse effects*; D006801:Humans; D008875:Middle Aged; D006435:Renal Dialysis / Q000379:methods*; D013927:Thrombosis / Q000209:etiology* / Q000628:therapy*
vernacular_title: Shunt de Thomas para hemodiálisis: disfunción y su tratamiento percutáneo.