Urinary stones are a rapidly spreading condition affecting about 10% of the population, driven by increasingly sedentary lifestyles and unbalanced dietary habits. When stones cannot be treated conservatively, the patient is referred for minimally invasive surgery. For years, our group has been studying not only the effectiveness of these procedures but, above all, their safety—for the kidney, the urinary system, and the patient’s overall health.
During flexible ureterorenoscopy, the surgeon inserts a thin instrument through the urinary tract up to the kidney, using a laser to碎石. However, the continuous flow of fluid needed to maintain visibility can increase intrarenal pressure, facilitating the entry of bacteria into the bloodstream and, in severe cases, leading to sepsis or septic shock. In a study of 369 patients who underwent surgery at our center, we analyzed the impact of the ureteral sheath— a hollow tubular device into which the ureterorenoscope is inserted, allowing fluid to drain freely outward and thereby reducing intrarenal pressure. Eighty-three percent of cases of septic shock occurred in patients operated on without a ureteral sheath, with a risk nearly 15 times higher than in those who used one. These results have reinforced the use of the ureteral sheath in our practice for patients with complex kidney stones, where prolonged operative time is anticipated and the risk of increased pressure is more significant [1].
Based on this experience, we adopted and studied the FANS (Flexible and navigable suction ureteral access sheath), a suction sheath that, in addition to passively draining fluid, applies gentle active suction, keeping intrarenal pressure even lower, improving surgical visibility, and reducing the risk of infection. In an ex vivo study using human kidneys, we demonstrated that the effectiveness of the FANS depends critically on the difference in caliber between the ureterorenoscope and the inner diameter of the sheath: when this difference is less than 2.5 French, suction fails to reduce pressure effectively. Not all instrument-sheath combinations are therefore safe, and this study provides, for the first time, a concrete threshold to guide device selection in the operating room [2].
The laser, the primary tool for breaking up stones, generates heat that spreads into the surrounding tissues: a phenomenon that is often underestimated but has the potential to cause damage to the ureteral mucosa or renal parenchyma. Our group was the first to quantify this phenomenon by introducing the concept of “thermal safety distance”: the distance from the laser fiber within which the accumulated thermal dose can cause tissue damage. The results are clear: at powers exceeding 20 W in the kidney and 10 W in the ureter, the risk persists even several millimeters from the fiber, and irrigation—while reducing the maximum temperature—does not eliminate it at high powers. These data provide the surgeon with a practical guideline for safely calibrating laser parameters [3].
For large stones or those located in complex areas, the alternative is miniaturized percutaneous nephrolithotomy, in which the surgeon creates direct access to the kidney through the skin. We compared the two approaches by analyzing 606 patients who underwent surgery between 2009 and 2025 at three referral centers, assessing renal function using estimated glomerular filtration rate and classifying acute complications according to internationally recognized criteria. In our study, no significant differences in changes in renal function were observed between the two approaches. In fact, patients with pre-existing reduced renal function tended to show improvement after surgery regardless of the technique used, confirming that stone removal is in itself a protective factor for the kidney. The choice between flexible ureterorenoscopy and miniaturized percutaneous nephrolithotomy should therefore be based on the characteristics of the stone and the surgeon’s experience, not on considerations of renal safety [4].
- Villa L, Dioni P, Candela L, et al. Understanding the Role of the Ureteral Access Sheath in Preventing Postoperative Infectious Complications in Patients with Kidney Stones Treated with Ureteroscopy and Ho:YAG Laser Lithotripsy: Results from a Tertiary Care Referral Center. J Clin Med. 2023;12(4):1457. Published Feb 12, 2023. doi:10.3390/jcm12041457
- Folcia A, Scilipoti P, Robesti D, et al. Ureteroscope-sheath size mismatch affects intrarenal pressure during suction-assisted flexible ureteroscopy: a human ex vivo study. BJU Int. 2026;137(6):973-975. doi:10.1111/bju.70212
- Ventimiglia E, Robesti D, Keller EX, et al. Temperature profile during endourological laser activation: introducing the concept of thermal safety distance. World J Urol. 2024;42(1):453. Published July 29, 2024. doi:10.1007/s00345-024-05162-3
- Candela L, Scilipoti P, Villa L, et al. A retrospective comparative analysis of changes in postoperative renal function following retrograde intrarenal surgery versus minimally invasive percutaneous nephrolithotomy (≤ 26Ch) using serum creatinine-based metrics. World J Urol. 2026;44(1):395. Published May 28, 2026. doi:10.1007/s00345-026-06490-2
