Yong DZ et al, 2011: Optimization of treatment strategy used during shockwave lithotripsy to maximize stone fragmentation efficiency
Yong DZ, Lipkin ME, Simmons WN, Sankin G, Albala DM, Zhong P, Preminger GM
Department of Surgery, Division of Urology, Duke University Medical Center, Durham, North Carolina, USA
BACKGROUND AND PURPOSE: Previous studies have demonstrated that treatment strategy plays a critical role in ensuring maximum stone fragmentation during shockwave lithotripsy (SWL). We aimed to develop an optimal treatment strategy in SWL to produce maximum stone fragmentation.
MATERIALS AND METHODS: Four treatment strategies were evaluated using an in-vitro experimental setup that mimics stone fragmentation in the renal pelvis. Spherical stone phantoms were exposed to 2100 shocks using the Siemens Modularis (electromagnetic) lithotripter. The treatment strategies included increasing output voltage with 100 shocks at 12.3 kV, 400 shocks at 14.8 kV, and 1600 shocks at 15.8 kV, and decreasing output voltage with 1600 shocks at 15.8 kV, 400 shocks at 14.8 kV, and 100 shocks at 12.3 kV. Both increasing and decreasing voltages models were run at a pulse repetition frequency (PRF) of 1 and 2 Hz. Fragmentation efficiency was determined using a sequential sieving method to isolate fragments less than 2 mm. A fiberoptic probe hydrophone was used to characterize the pressure waveforms at different output voltage and frequency settings. In addition, a high-speed camera was used to assess cavitation activity in the lithotripter field that was produced by different treatment strategies.
RESULTS: The increasing output voltage strategy at 1 Hz PRF produced the best stone fragmentation efficiency. This result was significantly better than the decreasing voltage strategy at 1 Hz PFR (85.8% vs 80.8%, P=0.017) and over the same strategy at 2 Hz PRF (85.8% vs 79.59%, P=0.0078).
CONCLUSIONS: A pretreatment dose of 100 low-voltage output shockwaves (SWs) at 60 SWs/min before increasing to a higher voltage output produces the best overall stone fragmentation in vitro. These findings could lead to increased fragmentation efficiency in vivo and higher success rates clinically.
J Endourol. 2011 Sep;25(9):1507-11. doi: 10.1089/end.2010.0732. Epub 2011 Aug 11
PMID: 21834658 [PubMed - in process]
This is an experimental in vitro study that gave further support to what has already been repeatedly shown, that a treatment strategy with step-wise increased shockwave power is better than step-wise decreased power. Moreover, it was shown that a shockwave frequency of 1 Hz resulted in a better disintegration than a frequency of 2 Hz. The low-to-high power approach also resulted in lower pre-focal cavitation activity. On the other hand focal cavitation activities were observed at higher levels of shockwave power.
The clinical conclusion drawn from this experimental study is that ESWL advantageously should start with at least 100 shockwaves at a low power level followed by step-wise increments and that a shockwave frequency of 1 Hz seems superior to higher frequencies.