Maximizing stone fragmentation efficiency with ultrasonic probes: impact of probe pressure and rotation.

Abstract

We examined the effects of probe rotation and pressure on stone fragmentation in an in vitro percutaneous nephrolithotomy model. The study was a fully randomized, factorial experiment with 20 repeat trials performed at each combination of variables, yielding a total of 300 trials per device for ultrasonic tests and 360 for ultrasonic/pneumatic combination tests. Varying masses were placed on the hand piece of each device to create a probe contact pressure of 400, 1,000 or 2,000 gm. The impact of rotation was tested only at 0 or 90 degrees and rotating only at a frequency of 2 Hz. Statistical analysis was performed using R, version 2.6.2. For the Cyberwand the Tukey HSD test showed that 400 and 1,000 gm probe pressure were significantly more effective than 2,000 gm pressure (p <0.05). The range and frequency of rotation were not statistically significant variables affecting Cyberwand efficiency. For the LithoClast Ultra using only the ultrasonic probe significant differences were found among the 3 pressure levels (400, 1,000 and 2,000 gm, respectively, p <0.05). For rotation 90 degrees were significantly more effective than 0 degrees (p <0.05) at a mean +/- SD stone mass of 0.168 +/- 0.078 and 0.107 +/- 0.09 gm, respectively. For the LithoClast Ultra ultrasonic/pneumatic combination 1,000 gm pressure were significantly more effective than 400 or 2,000 gm (p <0.05). The 6 and 12 Hz pneumatic frequencies outperformed 3 Hz but were not significantly different from each other (p <0.05). Differences in probe manipulation impact stone fragmentation efficiency and procedural success.