Preclinical Evaluation of a Newly Designed Ureteral Stent and Magnetic Retrieval Catheter for Minimally Invasive Stent Removal

Removal and repositioning of urinary tract implants by use of an endovascular snare system in dogs and cats (2013-2019)

OBJECTIVE

To report the fluoroscopic removal or repositioning of urinary tract implants in dogs and cats by use of an endovascular snare system (ESS) and to report procedural usefulness and complications in dogs and cats.

ANIMALS

3 cats and 14 dogs.

PROCEDURES

A medical records review was performed to identify dogs and cats that underwent removal or repositioning of urinary tract foreign bodies or implants by use of an ESS with fluoroscopic guidance at a veterinary teaching hospital from 2013 to 2019.

RESULTS

Dogs had a median weight of 25 kg (55 lb) with a range of 3.5 to 60.6 kg (7.7 to 133.3 lb), and cats had a median weight of 5 kg (11 lb) with a range of 4.2 to 5.4 kg (9.2 to 11.9 lb). By use of an ESS, 12 patients (2 cats and 10 dogs) underwent transurethral retrieval of retained vesicourethral implants or ureteral stents, 2 dogs underwent transurethral ureteral stent repositioning, 1 cat and 2 dogs underwent transnephric retrieval of ureteral stents, and 1 dog underwent cystoscopic-assisted transureteral ureteral stent retrieval. All procedures were successfully performed, and there were no associated procedural complications.

CONCLUSIONS AND CLINICAL RELEVANCE

Retained vesicourethral implants or ureteral stents were successfully retrieved by use of an ESS in dogs and cats transurethrally or with an open or percutaneous transnephric approach and fluoroscopic guidance. These techniques should be considered as an alternative or adjunct to more invasive methods for implant retrieval or manipulation.

Quantifying the forces needed for ureteral stent removal: Initial evaluation of magnetic stent removal devices on benchtop and porcine models

BACKGROUND

Indwelling ureteral stents are commonly used in pediatric surgeries for kidney stones and urinary tract obstruction, but often require instrumentation or anesthesia for removal. We evaluated the use of novel magnet devices to remove indwelling ureteral stents with a distally attached magnetic bead. Since the forces required for stent removal are unknown, we aimed to characterize and quantify the forces required for stent removal for future prototype testing.

METHODS

A custom 3-D urinary tract model was used for benchtop testing, and 6 female porcine subjects were used for in vivo testing after obtaining institutional approval. A modified porcine urethral model that patterned the human female urethral anatomy with approximately 4.5 cm urethral length was used. A HF-10 digital force gauge measured the force required to remove stents with varying properties (stent size, presence of curl, and size of distal magnetic bead). These force measurements were compared to the quantified magnetic forces generated by external magnets and catheter tip magnets. Furthermore, the magnetic retrieval devices were tested with various magnetic beads on both benchtop and porcine models.

RESULTS

The required force for removal of a 5 Fr x 14 cm double J stent was significantly higher in the benchtop model compared to the porcine model (4.7N v. 0.8N, p < 0.001). Forces of at least 1N were required from the external magnets to move the stent and bead across a 4-5 cm distance from the bladder neck to the urethral meatus. External magnets at a distance of 4-5 cm produced insufficient forces for removal, and thus they failed to remove the magnetic bead and stent from the bladder. The catheter-based retrieval device showed better success with a variety of different magnet pairs on the retrieval device and stent. Furthermore, the addition of saline to the bladder allowed for better retrieval rates of the smallest beads, even by the smallest magnetic tip catheters.

CONCLUSIONS

The forces required for ureteral stent removal are <1N in the porcine model, and improved benchtop models that emulate such parameters will facilitate future stent removal device testing. Given this threshold, external magnets did not generate sufficient force for stent removal at the required distance of 4-5 cm, whereas catheter tip magnetic retrieval overcomes the minimum distance limitation and showed successful retrieval. While these results are encouraging, further studies will define the optimal combination of catheter magnetic tip size and stent magnetic bead size.

Comparison of a magnetic retrieval device vs. flexible cystoscopy for removal of ureteral stents in renal transplant patients: A randomized controlled trial

INTRODUCTION

Placement of a ureteral stent at the time of renal transplantation can reduce complications when compared to non-stented anastomoses. Removal by flexible cystoscopy can be associated with discomfort, risk for infection, and high costs. New magnetic stents offer a means of bypassing cystoscopy by use of a magnetic retrieval device. Our objective was to compare clinical and cost-related outcomes of conventional and magnetic stents in patients undergoing deceased donor renal transplantation.

METHODS

Patients were randomized to receive either a conventional or a Black-Star^® magnetic stent. Clinical, procedural, and cost outcomes were assessed, and the Ureteral Stent Symptom Questionnaire (USSQ) was administered with the stent in situ and after stent removal. All variables were compared between groups.

RESULTS

Forty-one patients were randomized to conventional (n=19) or Black-Star (n=22) stent. The total time for stent removal under cystoscopy was significantly longer compared to Black-Star removal (6.67±2.47 and 4.80±2.21 minutes, respectively, p=0.019). No differences were found in the USSQ domains between groups. Rates of urinary tract infections and surgical complications between groups were similar. Stent removal was well-tolerated in both groups. Black-Star stent use resulted in a cost savings of $304.02 Canadian dollars (CAD) per case.

CONCLUSIONS

USSQ scores suggest that stent removal with the Black-Star magnetic stent is as equally well-tolerated as flexible cystoscopy by renal transplant patients. Black-Star stent removal was significantly faster than conventional stents. No differences in discomfort, infection rate, or complication rate were found. Use of the Black-Star stent resulted in an estimated annual savings of $27 360 CAD at our centre.

Ureteral stents in urolithiasis

Ever since the ureteral stent design was fitted with a curl on both sides to prevent it from migrating up or down the ureter some 40 years ago, its use has gained tremendous momentum, aiding in the rise and evolution of endourology and has confidently kept its place in modern time urology. Over the past four decades, several designs, coating and biomaterials have been developed, trying to reduce infection, encrustation and other stent related symptoms. As the ideal stent has not yet been discovered, different ways of helping patients with their complaints have been researched. This review will cover these aspects of stent use in urolithiasis.

Evaluation of pain perception associated with use of the magnetic-end ureteric double-J stent for short-term ureteric stenting

PURPOSE

To investigate the morbidity, complication rate, and pain perception during removal of a novel ureteric stent with a magnetic end using a-traumatic retrieval catheter.

METHODS

Between November 2013 and July 2015, 151 consecutive patients who underwent semirigid ureterorenoscopy (URS) for stone removal were prospectively enrolled. Stent removal was performed under local anesthesia using a special magnetic-end stent remover 1 week following URS. At follow-up, we obtained patients' medical history, urine culture result, renal ultrasonogram, and visual analog scale (VAS) score regarding stent irritation (VAS 1) and pain during removal (VAS 2).

RESULTS

Pain perception during stent removal was significantly less painful in patients with a magnet stent than in those with a regular stent (p < 0.001). Stent irritation was slightly higher in patients with an indwelling magnet stent than in those with a regular stent (p < 0.001). No significant differences in stent irritations were found in patients who had a magnetic stent for 4 weeks after laparoscopic pyeloplasty (p = 0.20). Patients with a magnetic stent experienced significantly less pain during removal with a median VAS 2 score of 2.5 and a mean VAS 2 score of 2.58 [standard deviation (SD) ± 0.90] than those without a magnetic stent a median VAS 2 of 6 and a mean VAS 2 of 5.88 (SD ± 1.43). The stent length correlated with stent irritation (p = 0.05), and it significantly correlated with pain during removal (p < 0.001).

CONCLUSION

The magnetic-end ureteric double-J stent is a safe option associated with less pain, particularly for male patients requiring short-term ureteric stenting.

Ultrasound-Guided Ureteral Stent Removal in Women

OBJECTIVES

The purpose of this study was to develop a fast, comfortable, and safe method of ureteral stent removal in women.

METHODS

From February 2014 to July 2015, a retrospective multicenter controlled study including 82 female outpatients was conducted. The control group was composed of 46 patients who underwent stent removal using a 22F cystoscope. The experimental group was composed of 36 patients who underwent stent removal under ultrasound guidance with a 15F spiral-ending device. Exclusion criteria were pelvic organ prolapse quantification stage II or higher and complicated stents (with migration or encrustation).

RESULTS

All studied patients had successful ureteral stent removal. No complications were seen in both groups. Differences between mean visual analog pain scale scores and stent removal durations were statistically significant in favor of the experimental group (P = .0077 and .0075, respectively).

CONCLUSIONS

The proposed method for ureteral stent removal in women under ultrasound guidance was shown to be faster and to have lower visual analog pain scale scores, in comparison with removal by a cystoscope, which makes it an attractive option for outpatient urologic praxis in uncomplicated cases, and because it is free of the risk of ionizing radiation and more comfortable, it can be used in pregnant patients.

Impact of ureteral stenting in ureteroscopy

PURPOSE OF REVIEW

We review new therapies and biomaterials designed to reduce ureteral stent symptoms in patients undergoing ureteroscopy.

RECENT FINDINGS

Pharmacologically, alpha blockers and antimuscarinics have been shown to have a synergistic effect and be more effective than either medication alone in reducing stent-related symptoms. Prestenting patients prior to ureterosocpy has been shown to be beneficial for patients with renal stones, offering a better stone-free rate and reduced complications, but not for ureteral stones. Stenting after use of a ureteral access sheath reduced complications and unscheduled emergency visits. Nonsteroidal anti-inflammatories have been shown to prevent pain after stent removal. Surveys showed that patients preferred to remove their own stents via dangle strings at home or undergo cystoscopic removal in the operating room with some type of anesthesia. New materials such as gel-based or biodegradable ureteral stents are being developed to deal with stent-related pain, encrustation, and infection. Antirefluxing stents eliminate vesicoureteric reflux in patients during voiding and may reduce symptoms of back and flank pain. Ureteral stents are involved in many procedures in urology and particularly kidney stone treatments.

SUMMARY

Advances in materials and medications will help improve the patient experience for those who receive a ureteral stent.