INTRODUCTION AND OBJECTIVE: Encrustation of indwelling ureteral stents can lead to ureteral obstruction, infection, and difficulty in stent removal. Improvements in materials and coatings have decreased this problem. In addition, stent geometry has been modified to further optimize flow dynamics and resistance. We tested flow and encrustation in a novel non-tubular ureteral stent in vitro with and without bacteria present.
METHODS: Novel 7 French Open-8 nontubular ureteral stents (Figure 1), including uncoated, hydrophilic, and hydrophilic-antimicrobial versions, were compared to standard 7 French tubular stents, including uncoated and hydrophilic stents (Boston Scientific Polaris, Bard Optima). In this in vitro model, peristaltic flow of 0.7 ml/min of urine analogue at body temperature was transferred from “kidney” to “bladder” tanks, through 10 French artificial ureter tubes containing the various stents. Stents were circumferentially compressed near the simulated ureterovesical junction. At variable time intervals, flow measurements were taken for the stents in each group. Stents were tested in triplicate. After 9 days, Proteus Mirabilis and Escherichia Coli bacteria were released into the system to facilitate encrustation. Encrustation was measured by the reduction in flow for each group.
RESULTS: In the absence of bacteria, flow rates were fastest in the hydrophilic tubular and antimicrobial Open 8 non-tubular stents. Two days following bacterial incubation, flow rates remained fastest for the hydrophilic tubular and antimicrobial non-tubular stents at 22-24 ml/min per stent. The uncoated non-tubular stent had a flow rate of 17ml/min, while the uncoated tube had a rate of 11 ml/min.
CONCLUSIONS: Of the two uncoated stents, the Open-8 non-tubular stent supported significantly improved urine flow versus the standard uncoated tubular stent. Although flow rates were initially similar, coatings play a substantial role in maintaining patency, especially as bacteria was added. It is probable that the antimicrobial and geometric properties of the hydrophilic-antimicrobial Open 8 stent provided an advantage in maintaining patency over the hydrophilic tubular stent in the presence of bacteria. The hydrophilic-antimicrobial nontubular Open-8 ureteral stent may provide another alternative for patients requiring long-term ureteral stenting and at high risk for stent encrustation and infection.
FIGURE 1. Cross Section of Open-8 stent