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

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. 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. 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. 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.