Ureteral catheters and stents are fundamental to the practice of Urology. These devices allow one to bypass and drain an obstructed ureter, determine urine output from a particular renal unit, and inject contrast to study the upper urinary tract. With the advent of newer methods to manage upper urinary tract stones (ESWL and ureteroscopy), the indications and use of ureteral catheters have and will continue to further increase.
The ideal ureteral catheter should allow one to measure urine output from a particular renal unit, drain even tenaciously purulent material, allow injection of contrast for imaging and finally remain indwelling and self contained if longterm ureteral stenting or drainage is required.
The presently available devices consist of external or internal ureteral catheters. Both types are usually passed through the ureteral meatus via a cystoscope, though they can be placed openly through different sites in the urinary tract.
Externalized ureteral catheters drain the upper urinary tract and pass through the bladder, exiting the urethra and draining into an external collecting device. They allow drainage through ports and a central lumen and can be irrigated as needed to drain tenacious and obstructing material. By draining externally, the output from the involved renal unit can be carefully monitored. Contrast can be injected as needed to evaluate the upper tract.
Unfortunately, these devices are not self contained and must be secured to an indwelling urethral catheter or they will migrate and be extruded by ureteral peristalsis. They therefore are not suitable for longterm outpatient care.
With this objective in mind, internalized ureteral catheters were developed. The most commonly used type is a plastic catheter with a curl at both the proximal and distal ends; i.e. Double J catheter. The curls are straightened over a central stiffening wire in order to pass the stent, but are reformed when the stiffening wire is removed. The proximal curl prevents distal migration and thereby keeps the device in the renal pelvis. The distal curl is positioned in the bladder to allow completely internalized drainage. No urethral catheter is needed to secure this type of stent, making it ideal for outpatient management.
U.S. Pat. No. 4,713,049 to Carter; 4,307,723 to Finney and 4,610,657 to Densaw all show this general approach while U.S. Pat 4,531,933 shows a variation of this concept by using helixes to replace hooks.
The devices shown by these patents, however, have disadvantages. The urine output from the involved renal unit can not be recorded as only total urethral urine output can be recorded and this would include both kidneys. Also, since the distal end of the catheter is internalized, it is not possible to irrigate the tube should it become obstructed. Under these circumstances the obstructed catheter could be more detrimental than beneficial as it would occlude an already narrowed ureteral lumen. Since the ureteral catheter can become obstructed without any external indication, the situation can become dramatically acute before it is realized that the internalized stent is no longer serving its purpose. Lastly, as the stent is not externalized, contrast cannot be injected if needed to image the upper tract.
A modification of the usual Double J catheter is available at present that allows injection of contrast via a small lumen--in the stiffening wire. This lumen however, is too small to allow reliable and accurate monitoring of urine output or drainage and irrigation of tenacious debris from the involved kidney.