Optimizing results of lithotripsy using robust electromagnetic probe

Background and Objective: A significant impediment to the measurement of th e pressures and forces created by lithotripter shockwaves has been their de structive properties, which have rendered most measuring devices impractica l, We have developed and tested a robust electromagnetic probe to measure c avitational forces in vitro in the focal zones of extracorporeal lithotript ers. The probe responds to the pressure gradient generated by the radial mo tion of cavitation bubbles, Materials and Methods: The effects of shockwaves from the Dornier MPL 9000 electrohydraulic lithotripter were measured over the lifetime of multiple e lectrodes. Results: The pulse energy from the electrodes dropped off rapidly after app roximately 50% of the lifetime quoted by the manufacturer. The electrodes w ere more efficient at higher power settings, As a result, we altered our pr otocol for the treatment of ureteral stones to use a higher kilovoltage and a second electrode whenever necessary. Stone-free rates after shockwave li thotripsy (SWL) in situ for stones <11 mm have increased from 68.2% to 83.3 %, and the retreatment rate has dropped from 23% to 15%, Despite significan tly higher power settings (23.7 kV v 18.7 kV; P <0.0001), the need for sedo analgesia has remained relatively constant (26% v 31%). Conclusions: Measurement of cavitational forces from lithotripters using a robust electromagnetic probe is useful in planning treatment strategy. We h ave demonstrated a clinically measurable improvement since implementing our new treatment protocol. Because the probe responds directly to cavitationa l forces, it should also prove useful for the objective comparison of diffe rent SWL machines.