Presented by: Yong Jie Jeremy Tay MBBS, MRCS
Singapore General Hospital

Introduction

Ureteral stents are widely used in our clinical practice to maintain a patent conduit between the kidney and bladder, which can be occluded due to urinary stones, urinary tract malignancies, extrinsic compression or strictures of the ureters. Physiologically, urine flow in an unidirectional way from the kidneys to the bladder via naturally occurring ureteral peristalsis and the occlusion of one way valve at the vesicoureteral junction. However, the presence of a ureteral stent inadvertently allows for urinary reflux by allowing a bidirectional flow and inactivating the physiological valve, especially in a high pressured bladder. This presents an inconvenient problem of reflux pyelonephritis which can be further compounded by a loss of renal function. 

 

The use of stents with anti-reflux properties have been postulated to reduce the incidence of pyelonephritis by reducing urinary reflux. Existing anti-reflux stents with its inherent design flaws have precluded its adoption in our clinical practice. Current solutions mainly address the intraluminal urinary reflux and neglects the prevention of extraluminal reflux. 

 

We aim to design an anti-reflux device which can be deployed onto ureteral stents, allowing unidirectional urinary drainage by reducing retrograde urinary flow in both a  intraluminal and extraluminal manner. The optimal skirting material type, length and angle is to achieve this objective is not known. Therefore, our bench study seeks to explore the optimal conditions for the purpose of designing this novel anti-reflux device. 

Materials

We 3D printed a 1:1 human urinary tract model with two pressure sensors placed in the ureter and bladder. A hand-applied bladder pressure was generated manually to stimulate bladder contractions and thus reflux pressure. The differential pressures between the bladder and ureter was measured. A combination of different angles (60°, 80°, 100°, 110°, 120° and 130°) and lengths of skirting (0.5, 1, 1.5 and 2cm) was evaluated.

Results

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Our study showed that the optimal skirting angle and length are 80° and 2cm respectively. Our anti-reflux device skirting design can effectively reduce pressure transmission from bladder to ureter in an ex vivo model. 

Conclusion

The study has provided evidence that the optimal skirting angle and length are 80° and 2cm respectively and that it can reduce pressure transmission from bladder to ureter in an ex vivo model. We aim to next experiment our prototype device in an in-vivo environment on a porcine model to further validate our results. 

Funding

NA

Lead Authors

Ya Dong Lu, MD, MRCS, FRCS
Singapore General Hospital

Kheng Sit Jay Lim, MBBS, MRCS, FRCS
Singapore General Hospital

Lay Guat Ng, MBBS, MRCS, FRCS
Singapore General Hospital