Polyethylene stent blockage: a porcine model

Background: Endoscopic insertion of biliary stents is a useful treatment fo r obstructive jaundice resulting from unresectable tumors of the pancreas a nd biliary tree. The main drawback is the recurrence of jaundice due to clo gging. The aim of this study was to establish an experimental model of poly ethylene stent clogging in large white pigs. Methods: A straight polyethylene stent of 5F (group I), 7F (group II) or 10 F size (group III) was inserted in the common bile duct. Animals were kille d at 2 months, or earlier if physical signs suggesting stent clogging occur red. Chemicophysical analysis of stent deposition combined stereomicroscopy and identification of the contents by means of Fourrier transform infrared spectroscopy. Bacteriologic analyses included identification of aerobic an d anaerobic bacteria and measurement of beta-glucuronidase, lecithinase and lipase activities. Results: Physical signs suggesting stent obstruction or death occurred in 8 of 8 animals in group I, 11 of 12 in group II, and 2 of 8 in group III (p < 0.001). The proportion of mucoprotein in the stent contents tended to fal l with increasing stent diameter (mean 82%, 58% and 47% for 5F, IF and 10F, respectively), whereas wheat starch and calcium bilirubinate content incre ased with increasing stent diameter (9% and 4%, 18% and 10%, and 29% and 23 % for 5F, 7 F and 10F, respectively), although none of these differences we re statistically significant. A variety of bacteria were cultured from the stent deposits, including anaerobic strains. Clostridium species were assoc iated with the highest enzyme activities. Conclusions: In this model the major component of early stent deposits was mucoprotein, and numerous aerobic and anaerobic bacteria were isolated. For mation of calcium bilirubinate was a late phenomenon and poorly related to bacterial enzymatic activities.