An algorithm based upon prognostic factors to guide patient selection when managing ureteric stones with Shock Wave Lithotripsy.
BAUS ePoster online library. Hemmant J. Jun 25, 2019; 259479; P11-5
Mr. Joshua Hemmant
Mr. Joshua Hemmant
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Shockwave lithotripsy (SWL) is considered to be an effective non-invasive treatment option for ureteric stones. The aim of this study was to create an algorithm based upon significant prognostic factors to guide patient selection for SWL.

Patients and Methods
We identified 150 patients attending for SWL for ureteric stones between October 2010 and February 2016. Data was collected retrospectively from electronic case notes and radiological images. All patients were treated with an on-site Storz Modulith SLX-F2 lithotripter. An algorithm was created using 'R'.


133 patients were treated and 66% of those were deemed radiologically stone free with SWL. Four factors were found to be independently statistically significant with regards to stone free status; age (p=0.003), Hounsfield units (p=0.002), prior nephrostomy insertion (p=0.022) and prior stent insertion (p=0.002). Our resulting algorithm is:
Probability of Success = 1 / (1 + Exp (-x))
x= 6.601-(0.043*Age) - (0.004*[Hounsfield Units]) - (1.694*[Has Neph]) - (2.761*[Has Stent])


Our SWL success would likely increase with improved patient selection. Age appears to be a novel significant factor in stone passage. This is an interesting observation worthy of further study given ageing populations in the developed world. It may be explained by difficult patient positioning or anatomical and physiological changes, as found in cadaveric and animal studies. The algorithm will require further validation in order to confirm our findings, however based upon our perfect predicted success model versus actual algorithm success, the results have proven very encouraging.
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