In vitro evaluation of nitinol urological retrieval coil and ureteral occlusion device: retropulsion and holmium...

Retropulsion of ureteral stones during laser lithotripsy may result in difficult and incomplete stone fragmentation. The Stone Cone nitinol urological retrieval coil and the NTrap nitinol ureteral occlusion device have been introduced into clinical practice to possibly limit stone retropulsion and enhance the efficiency of holmium laser (Convergent Laser Technologies, Alameda, California) stone fragmentation.

A total of 360 BegoStone Plus phantom stones (Bego USA, Smithfield, Rhode Island) of similar mass and weight were divided into 3 groups, including control, Stone Cone and NTrap. The groups were further subdivided according to fiber size (200 or 400 microm) and pulse width (350 or 700 microsec). These stones were placed in a horizontal pipette 12 mm in diameter, submerged in normal saline and disintegrated at laser settings of 1 J and 10 Hz continuously applied for 300 seconds. Retropulsion in cm and fragmentation efficiency with mass loss in mg were measured after treatment.

The 2 devices were effective for preventing retropulsion. In the control group the mean +/- SD retropulsion distance using a 350-microsec pulse width with the 200 and 400 microm fibers was 18.4 +/- 5.9 and 14.1 +/- 4.6 cm, while it was 6.2 +/- 2.6 and 5.6 +/- 2.4, respectively, using the 700-microsec pulse width. There was a statistically significant higher loss of stone weight in the Stone Cone and NTrap experimental groups than in the control group (p <0.0001). However, there was no difference between the 2 experimental groups across all groups (p = 0.32).

The Stone Cone and NTrap eliminated retropulsion and equally improved fragmentation efficiency. The maximum efficiency of fragmentation was seen using the 200 microm fiber at a 700-microsec pulse width.