The double-J ureteral stent: in vivo and in vitro flow studies

Although most ureters can now be stented, the rate of ureteral obstruction from extrinsic compression remains relatively high. To illuminate the mechanisms of obstruction in these patients we performed 20 in vivo pressure-flow investigations in 14 patients with indwelling ureteral Double-J stents. All patients had a percutaneous nephrostomy tube in place. Our investigations revealed proper drainage to the bladder in 17 of the 20 studies at an average renal pelvic pressure of 19.9 cm. water. Vesicorenal reflux was noted at an average bladder pressure of 20 cm. water in 17 studies. Three stents appeared to be obstructed. They showed no drainage to the bladder but also no reflux. To evaluate the in vivo results we then performed an in vitro study of pressure-flow characteristics under conditions simulating ureteral obstruction. At physiological flow rates different ureteral stents showed no major differences in pressure-flow characteristics. With compression and kinking, flow resistance in softer stents was notably greater than in hard stents. Therefore, we believe that in patients with suspected extrinsic compression of the ureter hard Double-J stents should be used. Vesicorenal reflux appears to be a reliable predictor of stent function.