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Skuginna V et al, 2015: Does Stepwise Voltage Ramping Protect the Kidney from Injury During Extracorporeal Shockwave Lithotripsy? Results of a Prospective Randomized Trial.

Skuginna V, Nguyen DP, Seiler R, Kiss B, Thalmann GN, Roth B.
Department of Urology, University of Bern, Bern, Switzerland.

Abstract

BACKGROUND: Renal damage is more frequent with new-generation lithotripters. However, animal studies suggest that voltage ramping minimizes the risk of complications following extracorporeal shock wave lithotripsy (SWL). In the clinical setting, the optimal voltage strategy remains unclear.
OBJECTIVE: To evaluate whether stepwise voltage ramping can protect the kidney from damage during SWL.
DESIGN, SETTING, AND PARTICIPANTS: A total of 418 patients with solitary or multiple unilateral kidney stones were randomized to receive SWL using a Modulith SLX-F2 lithotripter with either stepwise voltage ramping (n=213) or a fixed maximal voltage (n=205).
INTERVENTION: SWL.
OUTCOMES MEASUREMENTS AND STATISTICAL ANALYSIS: The primary outcome was sonographic evidence of renal hematomas. Secondary outcomes included levels of urinary markers of renal damage, stone disintegration, stone-free rate, and rates of secondary interventions within 3 mo of SWL. Descriptive statistics were used to compare clinical outcomes between the two groups. A logistic regression model was generated to assess predictors of hematomas.
RESULTS AND LIMITATIONS: Significantly fewer hematomas occurred in the ramping group(12/213, 5.6%) than in the fixed group (27/205, 13%; p=0.008). There was some evidence that the fixed group had higher urinary β2-microglobulin levels after SWL compared to the ramping group (p=0.06). Urinary microalbumin levels, stone disintegration, stone-free rate, and rates of secondary interventions did not significantly differ between the groups. The logistic regression model showed a significantly higher risk of renal hematomas in older patients (odds ratio [OR] 1.03, 95% confidence interval [CI] 1.00-1.05; p=0.04). Stepwise voltage ramping was associated with a lower risk of hematomas (OR 0.39, 95% CI 0.19-0.80; p=0.01). The study was limited by the use of ultrasound to detect hematomas.
CONCLUSIONS: In this prospective randomized study, stepwise voltage ramping during SWL was associated with a lower risk of renal damage compared to a fixed maximal voltage without compromising treatment effectiveness.
PATIENT SUMMARY: Lithotripsy is a non-invasive technique for urinary stone disintegration using ultrasonic energy. In this study, two voltage strategies are compared. The results show that a progressive increase in voltage during lithotripsy decreases the risk of renal hematomas while maintaining excellent outcomes.

Eur Urol. 2015 Jun 25. pii: S0302-2838(15)00520-5. doi: 10.1016/j.eururo.2015.06.017. [Epub ahead of print] 

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Comments 1

Hans-Göran Tiselius on Monday, 01 February 2016 11:44

The title of this article is interesting and indicates that the study will give an answer to the important question on whether SWL carried out with ”ramping” technique is less traumatic to the kidney than SWL at a standard “fixed” energy level. Unfortunately this question cannot be answered with the study design used by the authors.

The “ramping” method used in this report was considerably different from what most other SWL operators mean by “ramping”. In my understanding the purpose of stepwise increments in SWL power is to allow the kidney to adapt to the shockwaves and reduce the tissue trauma by vasoconstriction early during the treatment, induced by shockwaves at low energy levels. Moreover “ramping” results is a lower total energy load. The goal thereby is to increase the power slowly to a level necessary for optimal disintegration of the stones. In this study the authors started SWL at level 7 (Storz Modulith SLX F2 lithotripter). That is the power level usually considered to be maximal for treating stones in the kidney. That upper level has also been the rule that I personally have adhered to during more than 10 years’ work with this type of lithotripter. In this report: after 500 shockwaves at level 7 the power was increased in two steps to levels 8 and 9, when the “ramping” method was applied. The other group of patients was treated at fixed power: level 9! Level 9 is the highest energy that the lithotripter can provide and the manufacturers of the lithotripter have not recommended that level for disintegration of stones located in the kidney.

The frequency of hematomas in the “fixed” group was 13% compared with 5.6% in the “ramping” group. For both groups this frequency of ultrasound diagnosed hematomas was thus higher than that reported in most other studies and obviously at an unacceptably high level. The different outcome between the two treatment methods is most certainly explained by the fact that whereas the patients in the “fixed” power group had 100% of the 2500 shockwaves administered at level 9 (that is 385 J); the corresponding energy at that level for patients in the “ramping” group was only 40% (154 J)! It is not clear what the kV-values mentioned in the article really stand for. The energies calculated above are based on the Storz Medical Lithotripsy index (SMLI) corresponding to the energy in a circular area with a diameter of 12 mm in the shockwave focus. The total energy in the “fixed” group calculated in that way will be 385 J and in the “ramping” group 358 J. Although the total energy differs between the two groups, the distribution of shockwaves on different energy levels seems most important.

It had indeed been interesting to know how many hematomas that had been discovered with NCCT follow-up.

Although the results are inconclusive regarding the kidney protective value of a “ramping” procedure, as applied in this study, there is another lesson that probably can be learnt from the report and that is that the highest power (level 9) is unnecessary and associated with too high risk for tissue complications. The stone-free rates in the two groups were almost identical despite the fact that a much smaller number of shockwaves at level 9 were used for patients in the “ramping” group.

The patients in this study were treated under regional or general anaesthesia and therefore had no problems to tolerate the high power SWL. Despite this advantage the benefit of a proper ramping procedure is to early detect at which power level stones disintegrate, thus providing a tool for avoiding over-treatment.

The title of this article is interesting and indicates that the study will give an answer to the important question on whether SWL carried out with ”ramping” technique is less traumatic to the kidney than SWL at a standard “fixed” energy level. Unfortunately this question cannot be answered with the study design used by the authors. The “ramping” method used in this report was considerably different from what most other SWL operators mean by “ramping”. In my understanding the purpose of stepwise increments in SWL power is to allow the kidney to adapt to the shockwaves and reduce the tissue trauma by vasoconstriction early during the treatment, induced by shockwaves at low energy levels. Moreover “ramping” results is a lower total energy load. The goal thereby is to increase the power slowly to a level necessary for optimal disintegration of the stones. In this study the authors started SWL at level 7 (Storz Modulith SLX F2 lithotripter). That is the power level usually considered to be maximal for treating stones in the kidney. That upper level has also been the rule that I personally have adhered to during more than 10 years’ work with this type of lithotripter. In this report: after 500 shockwaves at level 7 the power was increased in two steps to levels 8 and 9, when the “ramping” method was applied. The other group of patients was treated at fixed power: level 9! Level 9 is the highest energy that the lithotripter can provide and the manufacturers of the lithotripter have not recommended that level for disintegration of stones located in the kidney. The frequency of hematomas in the “fixed” group was 13% compared with 5.6% in the “ramping” group. For both groups this frequency of ultrasound diagnosed hematomas was thus higher than that reported in most other studies and obviously at an unacceptably high level. The different outcome between the two treatment methods is most certainly explained by the fact that whereas the patients in the “fixed” power group had 100% of the 2500 shockwaves administered at level 9 (that is 385 J); the corresponding energy at that level for patients in the “ramping” group was only 40% (154 J)! It is not clear what the kV-values mentioned in the article really stand for. The energies calculated above are based on the Storz Medical Lithotripsy index (SMLI) corresponding to the energy in a circular area with a diameter of 12 mm in the shockwave focus. The total energy in the “fixed” group calculated in that way will be 385 J and in the “ramping” group 358 J. Although the total energy differs between the two groups, the distribution of shockwaves on different energy levels seems most important. It had indeed been interesting to know how many hematomas that had been discovered with NCCT follow-up. Although the results are inconclusive regarding the kidney protective value of a “ramping” procedure, as applied in this study, there is another lesson that probably can be learnt from the report and that is that the highest power (level 9) is unnecessary and associated with too high risk for tissue complications. The stone-free rates in the two groups were almost identical despite the fact that a much smaller number of shockwaves at level 9 were used for patients in the “ramping” group. The patients in this study were treated under regional or general anaesthesia and therefore had no problems to tolerate the high power SWL. Despite this advantage the benefit of a proper ramping procedure is to early detect at which power level stones disintegrate, thus providing a tool for avoiding over-treatment.
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