Stone geometry and structure dependence on extracorporeal shock wave lithotripsy.

The in vitro fragmentation effects of electromagnetic-induced shock wave lithotripsy (Siemens Lithostar) were studied on parallel laminated schists in relation to the incoming shock wave energy and the incoming angle of the incident shock wave. Well above the threshold energy, the total amount of acoustic energy required for fragmentation remained unchanged regardless of the power setting of the high-tension supply. The amount of energy transmitted to the stone was limited by a total reflection angle, restricting the available transmission surface. These observations determine the effect of shock waves on calculi with an irregular shape such as staghorn stones. Lithotripsy-induced cavitation has been recognized, but no immediate influence on disintegration has become apparent until now.

High pressure versus low pressure electromagnetic extracorporeal lithotripsy.

A low pressure and an upgraded high pressure electromagnetic lithotriptor were compared for the treatment of calculi within the ureter. The upgrading allows for increased energy density onto the stone surface. We targeted 139 ureteral calculi (average diameter 8.1 mm.) with the low pressure system. The mean number of shock waves was 7,308, 9,226 and 5,304 for calculi in the upper, mid and lower ureter, respectively, and the energy density corresponded to 0.222, mJ./mm.2, 0.224 mJ./mm.2 and 0.223 mJ./mm.2, respectively. Immediate fragmentation was achieved in 39 of 51 upper (77%), 21 of 42 mid (50%) and 22 of 46 lower (49%) ureteral calculi. The upgraded shock wave tube was used in 52 calculi (average diameter 6.1 mm.). The mean number of shock waves was 6,250, 14,150 and 3,400 for calculi in the upper, mid and lower ureter, respectively, and the energy density corresponded to 0.32 mJ./mm.2, 0.33 mJ./mm.2 and 0.30 mJ./mm.2, respectively. Immediate fragmentation was achieved in 11 of 16 upper (69%), 4 of 6 mid (67%) and 7 of 30 lower (23%) ureteral calculi. The comminution rate did not significantly increase, which implies that the focal energy density is not the only decisive parameter in fragmentation by extracorporeal shock wave lithotripsy.

Effect of alkalinization on calcium oxalate monohydrate calculi during extracorporeal shock wave lithotripsy: in vivo experiments.

Previous in vitro experiments demonstrated the reduced microhardness of calcium oxalate monohydrate (COM) calculi, relative to dry values, when saturated with an alkaline solution (pH = 9.5). Nineteen patients with a COM calculus in the distal ureter which had been resistant to prior extracorporeal shock wave lithotripsy in situ, were treated when the stone was surrounded by alkaline urine. The urine of 14 patients was alkalinized orally by administration of acetazolamine and citrate solution; in 5 other patients direct percutaneous irrigation of sodium bicarbonate via a nephrostomy tube was carried out. The urinary pH just before lithotripsy was greater than or equal to 9 in 17/19 patients. 4,000 shock waves, averaging 18.1 kV generated by the Siemens Lithostar, were delivered onto the calculus. No significant increase of comminution rate was apparent at radiographic control immediately after the treatment and only in half of the cases was evacuation obtained within 3 months.