In Vitro Evaluation of a Biliary Stent with an Anti-Duodenobiliary Reflux Valve Using Ox Bile Perfused At Physiological Bile Flow Rates

Abstract

In Vitro Evaluation of a Biliary Stent with an Anti-Duodenobiliary Reflux Valve Using Ox Bile Perfused At Physiological Bile Flow Rates Kulwinder S. Dua, B. Medda, I. Lang Background: A recent prospective randomized study on patients with biliary strictures showed that a plastic biliary stent with a windsock anti-duodenobiliary reflux valve (AR Stent) remained patent for a longer time compared to a standard stent(S Stent) (Dua, Gut 2005). In an earlier study, this AR Stent was evaluated in vitro using water perfused at 22-44 ml/min. Aim: The aim of the present study was to evaluate the AR Stent using bile instead of water perfused around physiological bile flow rates (0.5 to 1.5 ml per minute; Boyer J Clin Invest 1974; Hofmann Gastroenterology 1978). Method: A 10F, 7cm Tannenbaum stent was modified by attaching a 4 cm windsock valve at its duodenal end. Ox bile (Crescent Chemicals) at 37 C was perfused through the stent using a minimally compliant perfusion system with a pump (SP 100i Syringe Pump System, U.S.A.) where the flow rate was controlled electronically. Stents were placed horizontally at the level of the pressure transducer with the valve drooping downwards. At perfusion rates of 0.5 ml, 1 ml, and 2.5 ml per minute, basal and peak resistance pressures to antegrade flow were digitally recorded using the WinDaq Waveform Browser (Dataq Instruments U.S.A.). Anti-reflux ability of the stent was determined by placing the valve end of the stent into a glass chamber and recording the rise in pressure on reverse perfusion into the chamber. Antegrade and retrograde flow resistance pressures were compared with a standard Tannenbaum stent of same diameter and length. Results: Mean basal (perfusion pump off) and peak (perfusion pump on) pressure resistance offered by the AR and S stents to antegrade flow of bile are shown in table. Secondary to siphon effect of the valve, the AR stent generated negative pressures compared to the S stent. On reverse perfusion, the pressure within the glass chamber rose to the maximum allowed 320 mmHg with the AR stent. No such rise in pressure was noted with the S stent. Conclusions: Anti-reflux valve attached to a biliary stent does not offer increased resistance to the flow of bile but on the contrary may help antegrade flow by generating negative pressure by siphon effect. The valve is effective in preventing retrograde flow.