Impact of Colloidal Fluid on Stent Failure Under Extrinsic Ureteral Obstruction: An In Vitro Experimental Study.

Background and Purpose: Drainage of an obstructed kidney due to extrinsic ureteral obstruction (EUO) is imperative. Ureteral stents, commonly employed to facilitate drainage, often fail under EUO; this is usually attributed to external pressure over the ureter that occludes the stent lumen. We showed previously that external pressure and deformation of the ureter, alone, cannot explain frequent stent failure and speculated that colloids present in urine may play a critical synergetic role. In this study, we evaluate the role of colloidal fluid in ureteral obstruction under extrinsic compression. Materials and Methods: An in vitro ureter-stent model was employed using a latex tube to simulate a flexible ureter connecting simulated glass kidney and bladder units. The ureter was placed in deformed configuration of 40° with external pressure of 2000 g exerted over the deformed region of the stented ureter, representing extrinsic pressure. Four different ureteral stents were tested-4.8F, 6F, 7F, and 8F. Colloidal solution based on chicken albumin was injected through the simulated kidney into the stented ureter. Four replicates were performed for each stent diameter and straight stented ureters with no external pressure were used as controls. Stent failure was defined as kidney unit pressure over 10 cmH2O or complete obstruction of fluid flow; time to stent failure was measured. Results: Average failure time in 4.8F and 6F stents was 44 and 66 hours, respectively. The 7F ureteral stent failed in two replicates, after an average time of 75 hours, and continued to drain in the other two replicates. The 8F and control stents showed no change in kidney unit pressure in any of the replicates. Conclusions: Large-diameter stents are more effective in ureteral drainage under EUO in the presence of colloidal material in the fluid. Colloidal fluid may have a role in stent failure under EUO.

Urine flow analysis using double J stents of various sizes in in vitro ureter models.

A double J stent (DJS) is used to alleviate the congestion of urine in the upper urinary tract when there is ureteral stenosis, which causes the interruption of normal urine flow and results in renal failure. The purpose of placing DJSs is to ensure sufficient urine flow in the ureter, but the DJS acts as a foreign body in the urinary system and sometimes acts as an obstacle in achieving sufficient urine flow. Here, to evaluate the performance of various sizes of DJSs, 5Fr (1.666 mm) to 8Fr (2.666 mm), in the ureter, silicon ureter models without stenosis, and a circulation setup were constructed. The total flow rates (TFRs) in the stented ureters were evaluated with an in vitro experiment. The TFRs in the 5Fr DJS were larger than those in the other sizes of DJS. As the size of DJS increased, the TFR decreased. Computational fluid dynamics was also applied to validate the experimental results. It was shown that the experimental results agreed well with the numerical results.

A Prospective Randomized Comparison of a Covered Metallic Ureteral Stent and a Double-J Stent for Malignant Ureteral Obstruction.

Objective: To compare the safety and efficacy between a covered metallic ureteral stent (CMS) and a double-J ureteral stent (DJS) for the treatment of a malignant ureteral obstruction (MUO). Materials and Methods: Nineteen patients (seven men and 12 women; mean age, 53.4 years) were randomly assigned to the CMS (n = 10) or DJS (n = 9) group. The following were compared between the two groups: technical success, i.e., successful stent placement into desired locations; stent malfunction; stent patency, i.e., no obstruction and no additional intervention; complications; and patient survival. Results: The technical success rate was 100% in all 10 and 12 ureteral units in the CMS and DJS groups, respectively. During the mean follow-up period of 253.9 days (range, 63-655 days), stent malfunction was observed in 40.0% (4/10) and 66.7% (8/12) in the CMS and DJS groups, respectively. In the per-ureteral analysis, the median patency time was 239.0 days and 80.0 days in the CMS and DJS groups, respectively. The CMS group yielded higher patency rates compared with the DJS group at three months (90% vs. 35%) and at six months (57% vs. 21%). The overall patency rates were significantly higher in the CMS group (p = 0.041). Complications included the migration of two metallic stents in one patient in the CMS group, which were removed in a retrograde manner. The two patient groups did not differ significantly regarding their overall survival rates (p = 0.286). Conclusion: Covered metallic ureteral stent may be effective for MUO.

A Prospective Randomized Comparison of a Covered Metallic Ureteral Stent and a Double-J Stent for Malignant Ureteral Obstruction

OBJECTIVE: To compare the safety and efficacy between a covered metallic ureteral stent (CMS) and a double-J ureteral stent (DJS) for the treatment of a malignant ureteral obstruction (MUO). MATERIALS AND METHODS: Nineteen patients (seven men and 12 women; mean age, 53.4 years) were randomly assigned to the CMS (n = 10) or DJS (n = 9) group. The following were compared between the two groups: technical success, i.e., successful stent placement into desired locations; stent malfunction; stent patency, i.e., no obstruction and no additional intervention; complications; and patient survival. RESULTS: The technical success rate was 100% in all 10 and 12 ureteral units in the CMS and DJS groups, respectively. During the mean follow-up period of 253.9 days (range, 63–655 days), stent malfunction was observed in 40.0% (4/10) and 66.7% (8/12) in the CMS and DJS groups, respectively. In the per-ureteral analysis, the median patency time was 239.0 days and 80.0 days in the CMS and DJS groups, respectively. The CMS group yielded higher patency rates compared with the DJS group at three months (90% vs. 35%) and at six months (57% vs. 21%). The overall patency rates were significantly higher in the CMS group (p = 0.041). Complications included the migration of two metallic stents in one patient in the CMS group, which were removed in a retrograde manner. The two patient groups did not differ significantly regarding their overall survival rates (p = 0.286). CONCLUSION: Covered metallic ureteral stent may be effective for MUO.