Kaygısız O et al, 2017: Comparison of intermediate- and low-frequency shock wave lithotripsy for pediatric kidney stones.
Kaygısız O, Kılıçarslan H, Mert A, Coşkun B, Kordan Y.
Department of Urology, Faculty of Medicine, Uludağ University, Görükle, Bursa, 16059, Turkey.
The aim of the study to compare low and intermediate shock wave frequency rates in terms of success and complications for treating pediatric kidney stones. This retrospective study was performed on 58 consecutive pediatric patients (24 girls, 34 boys) who underwent shock wave lithotripsy (SWL) for kidney stones with an electrohydraulic lithotripter between April 2014 and March 2016. In the first year, all children underwent SWL with a frequency of 90 SWs/min as an intermediate frequency (Group 90), and in the second year all children were treated by SWL using 60 SWs/min as a low frequency (Group 60). The mean age of the patients was 5.87 ± 4.5 years. There were no significant differences in age, gender, stone characteristics and SWL energy level between the groups. Stone-free status was achieved in 14, 6 and 4 children in group 60; and in 10, 6 and 4 children in group 90 after one, two and three sessions, respectively. The stone-free rates were 80 and 74.1% after SWL and 90 and 88.9% after additional treatment in groups 60 and 90, respectively. The total median shock pulses were 2000 and 3600 in groups 60 and 90, respectively (p = 0.115). Efficiency quotients were 51.93 and 44.47 in groups 60 and 90, respectively. The mean total anesthesia times and complication rates did not differ between the groups. The low and intermediate frequency of SWL provided similar stone clearance in pediatric renal stones with similar anesthesia times. However, low SWL tended to need fewer shock pulses (2000/3600) for stone clearance, but the trend was not significant.
Urolithiasis. 2017 Jul 29. doi: 10.1007/s00240-017-1002-1. [Epub ahead of print]
Selection of the most appropriate effective SW-frequency remains an unresolved issue. That a high frequency is associated with a greater risk of tissue injuries is relatively well established, particularly when frequencies of 2 Hz or more were compared with lower frequencies.
The basic question is whether the disintegration with the low frequency (1 Hz) has an advantage over the intermediate (1.5 Hz) frequency and accordingly is more effective than high frequency treatment. But in this report no significant difference was observed. On the other hand if a low frequency is more effective; will it be necessary with the same total number of shockwaves? There are indeed two problems in this regard. It might occasionally be very difficult to know when to stop the treatment and a predetermined standard protocol is very often (and probably too often) applied.
In the children treated in this study the median age was lower in Group 60 than in Group 90 and even the trend of lower number of SWs in Group 60 can be questioned. What we really need is some reliable indicator that tells us when we have attained the optimal level of disintegration or perhaps indirectly when the first disintegration occurs.
The question is if a low frequency, as often stated, really prolongs the treatment or if it is reasonable to reduce the total number of SWs as a consequence of the improved disintegration at low frequency?
In a recent very interesting report  it was shown that an even lower frequency (0.5Hz) was surprisingly effective also for very large stones.
It is my impression that this field requires a lot of further research in order to avoid stereotypic treatment protocols based on pre-determined levels of SW-power, SW-frequency and SW-numbers.
1. Al-Dessoukey A, Abdalla, M, Sayed O, Abdalla R, Moussa A, Massoud A
Ultraslow high power SWL versus Slow power ramping SWL in stones with high attenuation value.
EAU17, London, Poster