Intrarenal thermal and pressure dynamics during ureteroscopy: an in vitro study

To evaluate in vitro determinants of intrarenal temperature (IRT) and pressure (IRP) during laser lithotripsy.

A silicone urinary tract model was used to perform laser lithotripsy on artificial stones placed in the renal pelvis. Three laser sources (thulium fibre laser, holmium:yttrium-aluminium-garnet [Ho:YAG] with Magneto Technology, and pulsed thulium:YAG) with 200-μm fibres were tested at four energy settings (0.6 J-10 Hz, 1 J-10 Hz, 0.2 J-50 Hz, and 1 J-40 Hz), delivering 2000 J per experiment. Irrigation was provided by gravity (40 cmH₂O) or hand-pump irrigation, combined with a standard ureteral access sheath (sUAS) or flexible and navigable suction sheath (FANS). Multivariable regression identified predictors of mean IRT and IRP.

Baseline temperatures were comparable among groups (27.2-32.2 °C, P > 0.05). Hand-pump irrigation reduced mean IRT compared to gravity (-9.1 °C, P = 0.001). Laser power showed a dose-response effect (10 W: +2.5 °C, P = 0.003; 40 W: +8.2 °C, P = 0.001 vs 6 W). At equivalent power and irrigation settings, laser source did not influence IRT under the experimental conditions evaluated. The thermal-risk threshold (>43 °C) was reached in 16.7% of experiments, increased with power (2.8%, 15.3%, and 41.7% at 6, 10, and 40 W; P = 0.001) and decreased with hand-pump irrigation and FANS (P < 0.05). Hand-pump irrigation increased IRP by 21 cmH₂O compared to gravity, while FANS reduced IRP by 12 cmH₂O vs sUAS (P = 0.001).

Mean IRT was associated with laser power and irrigation strategy. High-power settings (40 W) frequently exceeded the thermal-risk threshold. Although FANS was not associated with lower mean IRT, it reduced the likelihood of exceeding the thermal-risk threshold. Laser source had no effect on mean IRT when power and irrigation conditions were comparable. Mean IRP was influenced by irrigation strategy and UAS configuration but was not associated with mean IRT. These findings underscore the need for advanced integrated irrigation-aspiration systems capable of dynamic control of flow, pressure, and temperature to optimise procedural safety.