Veser J. et al., 2020: The effect of focus size and intensity on stone fragmentation in SWL on a piezoelectric lithotripter

Wednesday, 10 June 2020

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Veser J, Jahrreiss V, Seitz C, Özsoy M.
Department of Urology, Comprehensive Cancer Center, Medical Vienna General Hospital, University of Vienna, Waehringer Guertel 18-20, 1090, Vienna, Austria.
Department of Urology, Comprehensive Cancer Center, Medical Vienna General Hospital, University of Vienna, Waehringer Guertel 18-20, 1090, Vienna, Austria.
Karl Landsteiner SocietyUrology and Andrology, Vienna, Austria.

Abstract

PURPOSE: We aim to analyze the efficacy of different focus sizes and the influence of pulse pressure (intensity) during shock wave lithotripsy (SWL) in terms of stone fragmentation.

METHODS: Combination of three focal sizes (F1 = 2 mm, F2 = 4 mm, F3 = 8 mm) and 11 output pressure settings (intensity 10-20) of a piezoelectric lithotripter (Wolf PiezoLith 3000) were tested on artificial stones (n = 99). The stones were placed within a 2 mm mesh cage. The needed number of shockwaves (SW) to first visible crack, 50% and 100% stone disintegration were recorded.

RESULTS: Similar number of SW's were observed until the first crack 10, 11 and 11 SW's for F1, F2, and F3, respectively (p > 0,05). The median number of SW needed for 50% stone disintegration was 245 for F1 group, 242 for F2 group and 656 for F3 group. F1 vs F2 p = 0.7, F1 vs F3 and F2 vs F3 p < 0.05. Similarly, with larger focus size a higher number of shockwaves were necessary for 100% stone disintegration. 894, 877 and 1708 SW's for F1, F2 and F3, respectively. Only for F1 vs F3 and F2 vs F3 (all p < 0.05) a statistical difference was observed. These findings were consistent in all different power settings, with an increased difference in lower power levels (≤ 14).

CONCLUSIONS: A smaller focus size, as well as a higher peak pressure results in a more effective stone fragmentation. However, these results need to be confirmed in an in vivo setting with multiple parameters interfering the efficacy, like BMI, respiration or stone migration.
World J Urol. 2020 Jan 10. doi: 10.1007/s00345-019-03069-y. [Epub ahead of print].

Comments 1

Hans-Göran Tiselius on Wednesday, 10 June 2020 10:30

It is indeed surprising that 40 years after the introduction of SWL; the optimal relationship between the geometry of the focal volume and the energy density still is a matter of debate. That we so far do not have a definite answer to this important question reflects the currently rather weak interest in non-invasive stone removal.
In this report the authors carried out in vitro studies on piezoelectric lithotripsy with three different therapeutic settings: focal dimensions of 2, 3 and 4 mm.

The conclusion was that that a small focus diameter combined with high energy was most effective for disintegration of the artificial stones. It is of note, however, that clinical experience has shown that piezoelectric lithotripsy is less efficient than both electrohydraulic and electromagnetic lithotripsy. Moreover, it is well recognized that piezoelectric shockwaves disintegrate stones in a way different from that with the other two techniques. The interpretation of the in vitro studies reported in this article is hampered by the character of the artificial stones and uncertainty whether they reflect clinical conditions. Moreover, in every system in which stone fragments are eliminated from the stone container there are obvious differences from clinical conditions where fragments usually remain close to the stone.

There are experts with considerable experience in SWL that still claim that SWL with the original Dornier HM3 lithotripter is superior to achievements with any later generation lithotripter. It has, however, not been shown whether this is an effect of the lithotripter itself with electrohydraulic shockwaves, shockwave transmission without loss of energy or the kind of anaesthesia. My personal feeling is that modification of the original HM3-concept with a modified reflector and a capacitor of 40 nF rather than 80 nF was a great mistake. The reason was to make lithotripsy anaesthesia-free but from my own experience it was possible to use the original and unmodified Dornier HM3 lithotripter in essentially the same way with only analgesics and sedatives; a routine that was followed during eleven years; between 1987 and 1998. So, the question remains: which is the optimal focal volume?

The Table below shows some focus dimensions (mm) in commonly used lithotripters.

Large-focus devices marked in yellow.

In most modern lithotripters the focal volume is small. Important exceptions are the Medstone, Medispec and Xixin lithotripters.
The size limits for stones possible to treat with SWL has at least to some extent been an adaptation to the capacity of the lithotripters and possibly also to the energy delivery. From my personal experience it is obvious, that with a large focus lithotripter it was possible to successfully disintegrate larger stones than those that we currently treat with small- or medium size focal volume lithotripters. From a clinical perspective it would be interesting to have a lithotripter with two options: one with a focus size like that encountered in Storz Modulith lithotripters and one with a much larger focus as that in the original HM3, Medstone or Xixin. Unfortunately, the variable results published in the literature for different lithotripters are too difficult to analyse. Different stones were included, different principles of treatment and different routines for re-treatment of SWL were applied and,moreover, the interpretation of the outcome varies considerably from one centre to another.

The conclusion was that that a small focus diameter combined with high energy was most effective for disintegration of the artificial stones. It is of note, however, that clinical experience has shown that piezoelectric lithotripsy is less efficient than both electrohydraulic and electromagnetic lithotripsy. Moreover, it is well recognized that piezoelectric shockwaves disintegrate stones in a way different from that with the other two techniques. The interpretation of the in vitro studies reported in this article is hampered by the character of the artificial stones and uncertainty whether they reflect clinical conditions. Moreover, in every system in which stone fragments are eliminated from the stone container there are obvious differences from clinical conditions where fragments usually remain close to the stone.

There are experts with considerable experience in SWL that still claim that SWL with the original Dornier HM3 lithotripter is superior to achievements with any later generation lithotripter. It has, however, not been shown whether this is an effect of the lithotripter itself with electrohydraulic shockwaves, shockwave transmission without loss of energy or the kind of anaesthesia. My personal feeling is that modification of the original HM3-concept with a modified reflector and a capacitor of 40 nF rather than 80 nF was a great mistake. The reason was to make lithotripsy anaesthesia-free but from my own experience it was possible to use the original and unmodified Dornier HM3 lithotripter in essentially the same way with only analgesics and sedatives; a routine that was followed during eleven years; between 1987 and 1998. So, the question remains: which is the optimal focal volume?

The Table below shows some focus dimensions (mm) in commonly used lithotripters.

Large-focus devices marked in yellow.
[img]https://www.storzmedical.com/images/blog/Tiselius_020.JPG[/img]

In most modern lithotripters the focal volume is small. Important exceptions are the Medstone, Medispec and Xixin lithotripters.
The size limits for stones possible to treat with SWL has at least to some extent been an adaptation to the capacity of the lithotripters and possibly also to the energy delivery. From my personal experience it is obvious, that with a large focus lithotripter it was possible to successfully disintegrate larger stones than those that we currently treat with small- or medium size focal volume lithotripters. From a clinical perspective it would be interesting to have a lithotripter with two options: one with a focus size like that encountered in Storz Modulith lithotripters and one with a much larger focus as that in the original HM3, Medstone or Xixin.  Unfortunately, the variable results published in the literature for different lithotripters are too difficult to analyse. Different stones were included, different principles of treatment and different routines for re-treatment of SWL were applied and,moreover, the interpretation of the outcome varies considerably from one centre to another.

It is indeed surprising that 40 years after the introduction of SWL; the optimal relationship between the geometry of the focal volume and the energy density still is a matter of debate. That we so far do not have a definite answer to this important question reflects the currently rather weak interest in non-invasive stone removal. In this report the authors carried out in vitro studies on piezoelectric lithotripsy with three different therapeutic settings: focal dimensions of 2, 3 and 4 mm. The conclusion was that that a small focus diameter combined with high energy was most effective for disintegration of the artificial stones. It is of note, however, that clinical experience has shown that piezoelectric lithotripsy is less efficient than both electrohydraulic and electromagnetic lithotripsy. Moreover, it is well recognized that piezoelectric shockwaves disintegrate stones in a way different from that with the other two techniques. The interpretation of the in vitro studies reported in this article is hampered by the character of the artificial stones and uncertainty whether they reflect clinical conditions. Moreover, in every system in which stone fragments are eliminated from the stone container there are obvious differences from clinical conditions where fragments usually remain close to the stone. There are experts with considerable experience in SWL that still claim that SWL with the original Dornier HM3 lithotripter is superior to achievements with any later generation lithotripter. It has, however, not been shown whether this is an effect of the lithotripter itself with electrohydraulic shockwaves, shockwave transmission without loss of energy or the kind of anaesthesia. My personal feeling is that modification of the original HM3-concept with a modified reflector and a capacitor of 40 nF rather than 80 nF was a great mistake. The reason was to make lithotripsy anaesthesia-free but from my own experience it was possible to use the original and unmodified Dornier HM3 lithotripter in essentially the same way with only analgesics and sedatives; a routine that was followed during eleven years; between 1987 and 1998. So, the question remains: which is the optimal focal volume? The Table below shows some focus dimensions (mm) in commonly used lithotripters. Large-focus devices marked in yellow. [img]https://www.storzmedical.com/images/blog/Tiselius_020.JPG[/img] In most modern lithotripters the focal volume is small. Important exceptions are the Medstone, Medispec and Xixin lithotripters. The size limits for stones possible to treat with SWL has at least to some extent been an adaptation to the capacity of the lithotripters and possibly also to the energy delivery. From my personal experience it is obvious, that with a large focus lithotripter it was possible to successfully disintegrate larger stones than those that we currently treat with small- or medium size focal volume lithotripters. From a clinical perspective it would be interesting to have a lithotripter with two options: one with a focus size like that encountered in Storz Modulith lithotripters and one with a much larger focus as that in the original HM3, Medstone or Xixin. Unfortunately, the variable results published in the literature for different lithotripters are too difficult to analyse. Different stones were included, different principles of treatment and different routines for re-treatment of SWL were applied and,moreover, the interpretation of the outcome varies considerably from one centre to another.

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