Impact of negative-pressure ureteral access sheath on preventing "boiled ureter" during holmium laser lithotripsy

To evaluate the impact of negative-pressure ureteral access sheath (NP-UAS) on thermal effects during holmium laser lithotripsy.

A 3D-printed urinary model was used. A ureteroscope, traditional UAS (T-UAS) or NP-UAS, and a 200 µm hollium laser fiber were introduced into the model's proximal ureter, with the fiber activated for 90 s. Lithotripsy temperature (LT), irrigation flow rate (IFR), and intrarenal pressure (IRP) were measured during flexible ureteroscopic lithotripsy (fURL) and ureteroscopic lithotripsy (URL) using T-UAS or NP-UAS under varying irrigation pressures (IP) and laser powers.

During fURL at 10 kPa IP, the maximum LT exceeded 43 °C at laser powers of 20W, 30W, and 50W in the T-UAS group, while the NP-UAS group maintained LT < 43 °C. NP-UAS demonstrated significantly greater efficacy in controlling IFR and IRP compared to T-UAS (62.33 ± 2.35 vs. 24.01 ± 0.55 mL/min and 9.13 ± 0.21 vs. 1530.08 ± 112.43 Pa, respectively; p < 0.0001). At 20 kPa IP, only the T-UAS group exceeded a maximum LT of 43 °C at 50W, whereas the NP-UAS group remained below 43 °C. IFR and IRP measures for NP-UAS and T-UAS were 84.24 ± 1.74 mL/min vs. 46.31 ± 0.37 mL/min and 9.89 ± 0.15 Pa vs. 1646.61 ± 38.19 Pa, respectively (p < 0.0001). During URL, all groups maintained LT < 43 °C. At 10 kPa IP, IFR and IRP for NP-UAS and T-UAS were 78.28 ± 1.01 mL/min vs. 44.99 ± 1.09 mL/min and 4752.40 ± 267.72 Pa vs. 7769.63 ± 608.76 Pa, respectively (p < 0.0001). At 20 kPa IP, NP-UAS showed superior IFR (91.33 ± 4.46 mL/min vs. 78.48 ± 0.96 mL/min, p < 0.0001), with IRP exceeding measurement limits in both groups.

Increasing IFR reduces LT but elevates IRP. NP-UAS effectively maintains LT below critical levels while keeping IRP safe during both fURL and URL.