HOLMIUM-YAG LASER-INDUCED DAMAGE TO GUIDEWIRES - EXPERIMENTAL-STUDY

The holmium:YAG laser fragments stones of all compositions effectively . However, damage to ureteral guidewires by the laser has been describ ed, including in one of our own patients, in whom such damage resulted in morbidity. The purpose of this study was to characterize the inter action of Ho:YAG energy with guidewires in vitro. Seven ureteral guide wires were tested in a waterbath. The 365-mu m Ho:YAG laser fiber was placed at defined distances (0, 1, 2, 4, and 5 mm) from the guidewire. All guidewires were tested at angles of 0 degrees, 45 degrees, and 70 degrees from normal incidence. The minimum energy setting that result ed in structural damage to the guidewires was detected by endoscopic v ideo monitoring. All guidewires were susceptible to Ho:YAG laser damag e at modest energy settings. The energy required to produce visual dam age varied inversely with the square of the distance of the laser fibe r from the guidewire. At a distance of 5 mm, none of the guidewires wa s damaged, even at energy settings of 2.8 J (the maximum output from t he laser). The energy required to induce guidewire damage varied with the inverse of the cosine of the incident angle. The results demonstra te that no guidewire is immune from Ho:YAG laser damage when the fiber and guidewire are in contact. Caution must be exercised when operatin g the Ho:YAG laser near a guidewire, and guidewire integrity should be assured by the surgeon. Generally, the energy required to induce guid ewire damage exceeded lithotripsy levels at distances >1 mm and with h igher incident angles, implying a reasonable margin of safety during u reteroscopy. The pattern of energy thresholds required to induce damag e with respect to distance and incident angle suggests that the mechan ism of Ho:YAG lithotripsy is thermal.