Evidence-based choice of pneumatic lithotripsy probe diameter using an improvised in vitro biomodel

Over the past few years of experience at our center, we had perceived a difference in stone fragmentation capability between two probe diameters available for transurethral pneumatic lithotripsy. We designed and utilized a novel in vitro biomodel to test this hypothesis.

Twenty 15-cm-long pieces of avian gut were refashioned and fixed at the two ends in a standardized manner to imitate the natural human ureter and its convolutions as closely as possible. Five-millimeter phantom stones placed at the proximal 5-cm point of each ureter were fragmented by pneumatic lithotripsy through a semirigid ureteroscope in four study groups: Group I, using a 1.6-mm probe at 12 Hz; group II, using the 1.6-mm probe at 6 Hz; group III using a 0.8-mm probe at 12 Hz; and group IV using the 0.8-mm probe at 6 Hz.

Fragmentation required 272 +/- 57 pulses on the 1.6-mm probe, versus 853 +/- 85 using the 0.8-mm probe (P < 0.005). The 1.6-mm probe was similarly effective at 6 and 12 Hz (P = 0.08), while for the 0.8-mm probe 6-Hz pulse frequency entailed far fewer pulses to achieve the objective (P < 0.005). The 1.6-mm probe had uniformly higher efficacy compared to 0.8 mm at both 6 and 12 Hz (P < 0.005).

The 1.6-mm pneumatic lithotripsy probe has consistently higher efficacy compared to 0.8 mm throughout both frequency ranges. Our biomodel is introduced as a suitable low-cost and readily available in vitro medium for comparing intracorporeal lithotripsy modalities.