Ureteral Stent: Concept
An antimicrobial ureteral stent, which inhibits encrustation and bacterial colonization while maintaining patient comfort.
- Ureteral stent: resists migration, resists fragmentation, is kink resistant and radiopaque.
- Bacterial colonization: antimicrobial activity for up to two weeks.
- Patient Comfort: stent has a low coefficient of fiiction (value) for ease of insertion and will soften on implant at body temperature to maintain patient comfort.
Ureteral stents are used in urological surgery to maintain patency of the ureter to allow urine drainage from the renal pelvis to the bladder. These devices can be placed by a number of different endourological techniques. They are typically inserted through a cystoscope and may also be inserted intraoperatively. Indwelling ureteral stents help to reduce complications and morbidity subsequent to urological and surgical procedures. Frequently, ureteral stents are used to facilitate drainage in conjunction with Extracorporeal Shock Wave Lithotripsy (ESWL) and after endoscopic procedures. They are also used to internally support anastomoses and prevent urine leakage after surgery. Ureteral stenting may almost eliminate the urological complications of renal transplantation.
The advent of ESWL and the more recent barrage of endourological techniques have increased the indications for ureteral stents (Candela and Bellman 1997). Indications for use include:
- Treatment of ureteral or kidney stones
- Ureteral trauma or stricture
- Genitourinary reconstructive surgery
- Hydronephrosis during pregnancy
- Obstruction due to malignancy
- Retroperitoneal fibrosis
The need for ureteral stents range from a few days to several months. For patients with serious urological problems, ureteral stent maintenance may become a life-long necessity. Unfortunately, there are many problems associated with using ureteral stents.
Ureteric stenting difficulties
Trigonal irritation Haematuria Fever Infection Tissue inflammation Encrustation Biofilm formation
Kinking Ureteric rupture Ureteric perforation Stent misplacement Stent migration Stent misfit Stent forgotten Tissue hyperplasia
Today, elastomeric materials, such as silicones, polyurethanes and hydrogel-coated polyolefins are used, with no clear winner, which can withstand the urinary environment (Tunney et al., 1996). Although silicone has better long-term stability than other stent materials, its extreme flexibility makes it difficult to pass over guidewires and through narrow or tortuous ureters. Polyethylene is stiffer and easier to use for patients with strictures; however, it has been known to become brittle with time leading to breakage and is no longer commercially available. Polyurethane has properties that fall in between polyethylene and silicone; however, stent fracture also has been an issue with polyurethanes. Attempts have been made to develop polymers with a combination of the best of all properties. The key players are C-Flex (Concept Polymer Technologies), Silitek and Percuflex (Boston Scientific) (Roemer, 2000). C-Flex is proprietary silicone oil and mineral oil interpenetrated into a styrenelolefin block copolymer with the hope of reduced encrustation. Silitek (Medical Engineering Corporation) is another silicone-based copolymer. Percuflex is a proprietary olefinic block copolymer (Denstedt et al., 1998). Metallic stents have been used recently to treat extrinsic ureteric obstructions (Reinberg et al., 1994; Pauer et al., 1992). The effect of synthetic polymers on the urothelium of the urinary tract seems to be dependent on the bulk chemical composition of the polymer, the chemical composition of its surface, coatings on the device surface, smoothness of the surface and coefficient of friction (Denstedt et al., 1998). Typically, most ureteral stents are made of relatively smooth catheters. Koleski et al., (2000) tested a longitudinally grooved ureteral stent made by Circon in the pig ureter. The results indicated that the grooved stent led to better drainage than a conventional stent. Their