Optimizing stone harvesting in miniaturized-PCNL: a critical examination of renal access angles, technology, and the role they play in operative efficiency.

Abstract

Stone retrieval can be a laborious aspect of percutaneous nephrolithotomy (PCNL). A unique phenomenon of mini-PCNL is the vortex-effect (VE), a hydrodynamic form of stone retrieval. Additionally, the vacuum-assisted sheath (VAS) was recently developed as a new tool for stone extraction. The purpose of our study is to investigate the impact of renal access angle (as a surrogate for patient positioning) on stone retrieval efficiency and compare the efficiency among methods of stone retrieval. A kidney model was filled with 3mm artificial stones. Access to the mid-calyx was obtained using a 15Fr sheath. Stones were retrieved over three minutes at angles of 0°, 25°, and 75° utilizing the VE, VAS, and basket. Stones were weighed for comparison of stones/retraction and stones/minute. Trials were repeated three times at each angle. Renal access angle of 0° was associated with increased stone retrieval for both the VE and VAS (p < 0.05). The VE was the most effective method for stones retrieved per individual retraction at an angle of 0° (p < 0.005), although when analyzed as stones retrieved per minute, the VE and VAS were no longer statistically different (p = 0.08). At 75°, none of the methods were statistically different, regardless if analyzed as stones per retraction or per minute (p = 0.20-0.40). Renal access angle of 0° is more efficient for stone retrieval than a steep upward angle. There is no difference in stone retrieval efficiency between the VE and VAS methods, although both are superior to the basket at lower sheath angles.