Watt's the difference? A randomised trial of high- vs low-power ureteroscopic thulium fibre laser lithotripsy.

OBJECTIVE: To compare operative time and clinical outcomes between high-power (HP) and low-power (LP) thulium fibre laser (TFL) ureteroscopic (URS) lithotripsy for renal stones. PATIENTS AND METHODS: Single-centre, randomised trial (1:1) at Haukeland University Hospital, Norway. Adults undergoing day-case URS for 8-25 mm renal stones were enrolled. A total of 150 cases were included. Patients were randomised to URS lithotripsy with TFL using HP (16-18 W, selected for thermal safety during sheathless URS) or LP (4-6 W). The primary endpoint was operative time. The secondary endpoints were stone-free rate (SFR) on 3-month non-contrast computed tomography (Grade A: no residuals; Grade B: ≤2 mm; Grade C: ≤4 mm; Grade D: >4 mm), laser metrics, performance measures, and complications according to the Clavien-Dindo Classification. Groups were compared using appropriate parametric and non-parametric tests (two-sided α = 0.05). RESULTS: A ureteric access sheath was not used in any case, reflecting routine practice at our centre. The operative time did not differ between arms: median (interquartile range) HP 48 (36-62) vs LP 54 (42-65) min (P = 0.12). HP used more energy (12 vs 7 kJ, P < 0.001) with shorter active laser time (13 vs 24 min, P < 0.001), but laser operating time was similar. SFRs favoured LP compared to HP: Grade A, 63% vs 44% (P = 0.02); Grade B, 77% vs 56% (P = 0.008). The Grade C SFR was similar between arms. LP was also associated with better surgeon-rated endoscopic visibility and fewer minor postoperative complications (11% vs 37%, P < 0.001). Major complications (Clavien-Dindo Grade ≥III) were uncommon and similar between arms. CONCLUSION: Using HP did not shorten the operative time. LP improved SFRs for Grade A/B and reduced minor postoperative morbidity, supporting LP as the default TFL strategy for sheathless URS lithotripsy.