Impact of holmium laser settings and fiber diameter on stone fragmentationand endoscope deflection

We compared the impact of various energy settings, frequency, and fiber dia meters on the stone fragmentation capabilities of the holmium laser. Stone phantoms, made from plaster of Paris and uniform in weight, were treated wi th one of two laser fiber sizes: small (200 and 365 mu m) and large (550 an d 1000 mu m). Stones were immersed in water and fragmented for 3 minutes at 0.5, 1.0, or 2.0 J and 5, 10, or 15 Hz. The mean percentage decrease in we ight in the two groups was compared using one-way ANOVA. The effect on flex ible ureterorenoscope deflection of the small fibers was tested in two diff erent ureterorenoscopes. Raising the energy level when using the small fibe rs resulted in more weight loss (P < 0.05). Increasing the frequency up to 10 Hz also resulted in a significant increase in weight loss (P < 0.05), ye t above 10 Hz, there was no significant additional weight loss noted for ei ther small fiber. There was no significant difference in the weight loss pr oduced by the two fibers unless the energy setting was >1.0 J. Studies with the large fibers demonstrated similar results, with significant increments of weight loss occurring with increased energy (P < 0.05), while nonsignif icant differences were seen for the two fiber diameters. Increasing laser f requency up to 15 Hz resulted in a significant increase in weight loss for the large fibers. Loss of ureterorenoscope deflection ranged from 7% to 16% and 18% to 37% for the 200-mu m and 365-mu m fibers, respectively. Small-d iameter fibers, in combination with semirigid or flexible ureteroscopes, sh ould be used to treat upper urinary tract stones. The 365-mu m fiber should be utilized for the management of ureteral stones, as minimal endoscopic d eflection is required to access these calculi. Because the 200-mu m fibers are considerably more expensive, their use should be reserved for fragmenta tion of intrarenal calculi, where maximum deflection is required during fle xible ureterorenoscopy. The ideal energy and frequency settings for the sma ll fibers are <1.0 J and 5 to 10 Hz. Larger fibers can be used for managing bladder or renal calculi, as there is no need for significant fiber deflec tion. The 550-mu m fiber is preferred, as it is comparable in efficacy to t he 1000-mu m fiber and is less expensive. Energy and frequency can be maxim ized to 2.0 J and 15 Hz without damage to the fiber, but visibility can be affected by high frequencies. Appropriate fiber selection and energy/freque ncy settings will allow access to most stones throughout the urinary tract, maximize fiber life, and minimize fiber expense.