Clogging of biliary endoprostheses: a new perspective.

Endoscopic palliation with biliary endoprostheses is now an established treatment for benign and malignant strictures of the biliary tree. These endoprostheses, however, tend to clog with time. We investigated this problem by undertaking in vitro studies on stents of different designs made of different polymer materials. The stent that performed best was then tested in an in vivo trial. There was a direct relation in vitro between the frictional coefficient of a polymer and the amount of encrusted material. Catheters perfused in bacterially contaminated bile, irrespective of material and design, accrued significantly more sludge than catheters perfused with sterilised bile. The presence of side holes significantly increased the amount of sludge in the stents, but eliminated any differences between the various materials. We therefore investigated the effect of omitting side holes in a clinical trial which consisted of two groups of 20 patients each. The group treated with conventional stents accrued significantly more sludge in the stents than the group treated with experimental stents without side holes (p less than 0.05). The absence of side holes did not cause incomplete drainage or increase morbidity. Side holes are detrimental to stent patency, which is adversely affected by other factors including bacteria and proteins.

A placebo-controlled study on the efficacy of aspirin and doxycycline in preventing clogging of biliary endoprostheses.

Sixty patients in whom a biliary endoprosthesis was inserted were randomized to receive: (1) placebo, (2) aspirin, or (3) doxycycline, to study the effect on the process of sludge formation. After 2 months all endoprostheses were changed, and the amount and composition of the sludge in the patent stents was analyzed. Half of the patients dropped out. The major component (56%) of the sludge of all groups was protein. No insoluble residue was present. Major deposits of sludge were found at irregularities in the stent wall (side flaps). Both doxycycline and aspirin reduced the dry weight of the sludge. Doxycycline significantly reduced the amount of protein, but scanning electron microscopy still showed abundant bacterial growth. Aspirin reduced the content of all sludge components including protein, suggesting that it decreases "stickiness" of bile. Surprisingly, doxycycline significantly decreased the death rate in the 2 months of the study. We present further evidence for a primary role of protein deposition in the early stages of stent occlusion. This process can be partly inhibited by doxycycline and probably also by aspirin, which could lead to a significant increase in stent patency.