Quantifying the forces needed for ureteral stent removal: Initial evaluation of magnetic stent removal devices on benchtop and porcine models. Issue 5 (October 2020)

• Record Type: Journal Article
• Authors: Sheth, Kunj R.; White, Jeffrey T.; Puttmann, Kathleen; Waters, David; Soto, Matias; Bell, Martin; Aboufadel, Tasha; Heffernan, Michael J.; Richardson, Eric; Song, Sang Hoon; Koh, Chester J.
• Is Part Of: Journal of pediatric urology. Volume 16:Issue 5(2020)
• Page Start: 596.e1
• Page End: 596.e8
• Publication Date: 2020-10
• Subjects: Ureteral stent -- Pediatric -- Preclinical studies -- Magnetic force -- Animal models -- Porcine; UPJ Ureteropelvic Junction -- 3-D 3-Dimensional -- LRS Lactate Ringer's Solution -- Fr French; Pediatric urology -- Periodicals; Urologic Diseases -- Periodicals; Urogenital Diseases -- Periodicals; Urologic Surgical Procedures -- Periodicals; Child; Infant; Urologie pédiatrique -- Périodiques; Appareil urinaire -- Maladies -- Périodiques; Pédiatrie; Urologie; Pediatric urology; Périodique électronique (Descripteur de forme); Ressource Internet (Descripteur de forme); Electronic journals; Periodicals; Electronic journals; 618.926
• DOI: 10.1016/j.jpurol.2020.03.020
• Languages: English
• ISSNs: 1477-5131

Abstract

Summary: 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. Extended Summary Table Maximum forces required to remove ureteral stents with varying properties (stent size, presence of curl, size of distal magnetic bead) from the bladder in both benchtop and porcine models. For the benchtop model, the stents were placed solely in the bladder and then also in the ureter with just the distal coil in the bladder. In the porcine model they were all placed in the ureter. With the exception of the porcine model 4 Fr trials (n = 3, 5 for 4 Fr straight and 4 Fr JJ respectively), all conditions are based on n = 9 trials or greater. Entries marked with ∗∗∗ are significantly different from the values for the corresponding stent type in the benchtop bladder model to the p = 0.01 level using a two-tailed student's t-test Extended Summary Table BENCHTOP - Max Retrieval Force in N PORCINE - Max Retrieval Force in N Stent size + bead type Bladder Ureter Ureter 5 Fr JJ, stent unfurling only 0.79 ± 0.22 4 Fr Straight 0.17 ± 0.04 5 Fr Straight 0.29 ± 0.16 4.20 ± 0.62 ∗∗∗ 0.23 ± 0.06 4 Fr JJ 0.55 ± 0.08 5 Fr JJ 0.79 ± 0.23 4.73 ± 0.65 ∗∗∗ 0.82 ± 0.40 5 Fr JJ + 2 mm 0.85 ± 0.45 5 Fr JJ + 3.2 mm 0.99 ± 0.14 4.05 ± 0.59 ∗∗∗ 0.81 ± 0.38 5 Fr JJ + 4.8 mm 1.68 ± 0.16 3.92 ± 0.66 ∗∗∗