Technical considerations using a pulsed neodym-YAG laser for endoscopic shock wave lithotripsy.

First clinical experience with the use of a Q-switched pulsed Neodym-YAG Laser showed promising results. This paper focuses on two problems with respect to the optimal use of this laser: (1) is there any need for a special iron (Fe3+)-enriched irrigant, and (2) what is the best frequency for laser lithotripsy? To answer these questions, we used an in vitro model, measuring the laser-induced breakdown (LIB) photographically utilizing sodium chloride as an irrigant enriched with different amounts of Fe3+ ions. The disintegrative efficacy of the laser was tested utilizing a standard stone model (plaster cube) and working at different frequencies (1, 10, 40 Hz). The addition of Fe3+ ions resulted in significant improvement of LIB. However, in the presence of a test stone no difference between sodium chloride and Fe3+-enriched irrigants was noted. The use of lower frequencies (1, 10 Hz) lead to a remarkable improvement in the disintegrative efficacy of the laser compared to the standard frequencies (40, 50 Hz). For clinical use, addition of Fe3+ ions seems only necessary if optical breakdown (LIB) is insufficient despite the increase in generator voltage. In such a situation, we recommend the addition of an 1-ml Fe3+ solution to 10 liters of sodium chloride irrigant (= 0.5 mg Fe3+/dl). Moreover, the standard frequency for laser-induced intracorporeal lithotripsy should be 1-10 Hz.