Keskin SK et al., 2022: The New Lithotripsy Index predicts success of shock wave lithotripsy

Monday, 27 March 2023

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Keskin SK, Spencer M, Lovegrove C, Turney BW.
Urology Department, Oxford University Hospitals NHS Foundation Trust, Oxford, UK.
Department of Urology, Bahcesehir University Medical School, Istanbul, Turkey.
Radiology Department, Oxford University Hospitals NHS Foundation Trust, Oxford, UK.
Urology Department, Oxford University Hospitals NHS Foundation Trust, Oxford, UK.

Abstract

Aim: The aim of this study is to evaluate the factors affecting treatment success in patients who underwent Shock wave lithotripsy (SWL) and to investigate the effect of the Storz Medical Lithotripsy Index (SMLI) on treatment effectiveness.

Methods: Prospective data were collected on patients undergoing SWL treatment for kidney stones between January 2013 and May 2021. Stone location, number and size were determined with non-contrast CT (NCCT) for all patients. All patients underwent SWL with a Storz Modulith SLK lithotripsy machine without anaesthesia. The total amount of energy applied to the stone was calculated using the SMLI. All patients were evaluated for stone-free status by X-ray at least 2 weeks after treatment. The success of the procedure was defined as the patient being completely stone free or the detection of residual fragments < 4 mm that did not require further treatment.

Results: A total of 1230 patients with kidney stones were included in the study. The mean age of the patients was 42.33 ± 11.78 (18-75), and the mean BMI was 28.47 ± 8.78 (19.25-38.52). During SWL, 75.6% of patients demonstrated excellent pain tolerance (930/1230). A total of 116 patients could not tolerate the pain during SWL (9.4%). Treatment success was associated with fewer treatment sessions (2.34 ± 1.75 vs. 2.90 ± 2.04; p < 0.001), smaller stone size (7.52 ± 3.29 vs 8.60 ± 3.93; p < 0.001) and higher SMLI/stone size (25.11 ± 13.63 vs. 22.27 ± 14.50; p < 0.001). In the univariate and multivariate regression analysis, the factors affecting the success of the treatment were the number of sessions (OR 1.170), stone size (OR 1.142), number of shocks (OR 1.005), SMLI/stone size (OR 1.024) and pain tolerance (OR 0.692).

Conclusion: In the treatment of kidney stones with SWL, stone site, stone size, SMLI/stone size, and pain tolerance are the factors affecting success. SMLI per stone size is a statistically significant factor for predicting SWL success.
World J Urol. 2022 Dec;40(12):3049-3053. doi: 10.1007/s00345-022-04215-9. Epub 2022 Nov 15. PMID: 36380209

Comments 1

Othmar Wess on Monday, 27 March 2023 10:30

Keskin et al. look at parameters which can predict the success of lithotripsy procedures such as:

“Appropriate patient selection, improved SWL efficacy and
optimal disease management. In the current literature, there
are various reported factors that can affect stone clearance rates. Clinical parameters such as the patient's body mass index, stone location, skin-to-stone distance, stone
diameter or stone volume and Hounsfield unit values are
among the strong predictive parameters for treatment success”

SWL efficacy is amongst others a mandatory precondition for treatment success. If all the above listed requirements are sufficiently fulfilled, fragmentation efficiency is the crucial factor. Stone fragmentation depends on the interaction of shock waves with brittle stones. This is a complex physical process based on forces generated by reflection of shock waves (1) and the energy delivered by the shock waves.
The medical operator of a lithotripter machine controls the number of shocks and the energy per shock and can vary these parameters during the treatment to adapt to pain sensation and intended progress of fragmentation. Treatment protocols usually document number of shock waves and energy level used.

Storz Medical SWL devices records the total energy applied to the focal area with a diameter of 12 mm using the Storz Medical Lithotripsy Index (SMLI).
The SLMI counts the energy of each single shot and its current energy content at the selected energy level within a 12 mm circle at the focal point. At the end of treatment procedure, the SLMI indicates the total energy delivered to the focal area with diameter of 12mm.

This is the maximum energy exposed to stones with a diameter of 12 mm or more. Smaller stones are exposed to slightly less energy. A further reduction of effective energy hitting the stone occurs when the position of the stone is not exactly in the focal area e.g., due to respiratory dislocation.
The energy that paths the stone without affecting on the stone has only little effect on the surrounding tissue since strong forces capable to fragmentize are generated specifically on stones and not on soft tissue.
The SMLI is a measure of the total shock wave dose (energy) the stone is exposed to when located in the forcal area.
This parameter correlates positively with the treatment success as the authors confirmed by statistical analysis their treatment data of significant number of patients.
1. Wess, O.J., Mayer, J. Fragmentation of brittle material by shock wave lithotripsy. Momentum transfer and inertia: a novel view on fragmentation mechanisms. Urolithiasis 48, 137–149 (2020). https://doi.org/10.1007/s00240-018-1102-6

Othmar Wess

Keskin et al. look at parameters which can predict the success of lithotripsy procedures such as:

“Appropriate patient selection, improved SWL efficacy and
optimal disease management. In the current literature, there
are various reported factors that can affect stone clearance rates. Clinical parameters such as the patient's body mass index, stone location, skin-to-stone distance, stone
diameter or stone volume and Hounsfield unit values are
among the strong predictive parameters for treatment success”

SWL efficacy is amongst others a mandatory precondition for treatment success. If all the above listed requirements are sufficiently fulfilled, fragmentation efficiency is the crucial factor. Stone fragmentation depends on the interaction of shock waves with brittle stones. This is a complex physical process based on forces generated by reflection of shock waves (1) and the energy delivered by the shock waves.
The medical operator of a lithotripter machine controls the number of shocks and the energy per shock and can vary these parameters during the treatment to adapt to pain sensation and intended progress of fragmentation. Treatment protocols usually document number of shock waves and energy level used.

Storz Medical SWL devices records the total energy applied to the focal area with a diameter of 12 mm using the Storz Medical Lithotripsy Index (SMLI).
The SLMI counts the energy of each single shot and its current energy content at the selected energy level within a 12 mm circle at the focal point. At the end of treatment procedure, the SLMI indicates the total energy delivered to the focal area with diameter of 12mm.

This is the maximum energy exposed to stones with a diameter of 12 mm or more. Smaller stones are exposed to slightly less energy. A further reduction of effective energy hitting the stone occurs when the position of the stone is not exactly in the focal area e.g., due to respiratory dislocation. 
The energy that paths the stone without affecting on the stone has only little effect on the surrounding tissue since strong forces capable to fragmentize are generated specifically on stones and not on soft tissue.
The SMLI is a measure of the total shock wave dose (energy) the stone is exposed to when located in the forcal area.
This parameter correlates positively with the treatment success as the authors confirmed by statistical analysis their treatment data of significant number of patients.
1.	Wess, O.J., Mayer, J. Fragmentation of brittle material by shock wave lithotripsy. Momentum transfer and inertia: a novel view on fragmentation mechanisms. Urolithiasis 48, 137–149 (2020). https://doi.org/10.1007/s00240-018-1102-6

Othmar Wess

Keskin et al. look at parameters which can predict the success of lithotripsy procedures such as: “Appropriate patient selection, improved SWL efficacy and optimal disease management. In the current literature, there are various reported factors that can affect stone clearance rates. Clinical parameters such as the patient's body mass index, stone location, skin-to-stone distance, stone diameter or stone volume and Hounsfield unit values are among the strong predictive parameters for treatment success” SWL efficacy is amongst others a mandatory precondition for treatment success. If all the above listed requirements are sufficiently fulfilled, fragmentation efficiency is the crucial factor. Stone fragmentation depends on the interaction of shock waves with brittle stones. This is a complex physical process based on forces generated by reflection of shock waves (1) and the energy delivered by the shock waves. The medical operator of a lithotripter machine controls the number of shocks and the energy per shock and can vary these parameters during the treatment to adapt to pain sensation and intended progress of fragmentation. Treatment protocols usually document number of shock waves and energy level used. Storz Medical SWL devices records the total energy applied to the focal area with a diameter of 12 mm using the Storz Medical Lithotripsy Index (SMLI). The SLMI counts the energy of each single shot and its current energy content at the selected energy level within a 12 mm circle at the focal point. At the end of treatment procedure, the SLMI indicates the total energy delivered to the focal area with diameter of 12mm. This is the maximum energy exposed to stones with a diameter of 12 mm or more. Smaller stones are exposed to slightly less energy. A further reduction of effective energy hitting the stone occurs when the position of the stone is not exactly in the focal area e.g., due to respiratory dislocation. The energy that paths the stone without affecting on the stone has only little effect on the surrounding tissue since strong forces capable to fragmentize are generated specifically on stones and not on soft tissue. The SMLI is a measure of the total shock wave dose (energy) the stone is exposed to when located in the forcal area. This parameter correlates positively with the treatment success as the authors confirmed by statistical analysis their treatment data of significant number of patients. 1. Wess, O.J., Mayer, J. Fragmentation of brittle material by shock wave lithotripsy. Momentum transfer and inertia: a novel view on fragmentation mechanisms. Urolithiasis 48, 137–149 (2020). https://doi.org/10.1007/s00240-018-1102-6 Othmar Wess

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