Ureteral access sheath-related injuries vs. post-operative infections. Is sheath insertion always needed? A prospective randomized study to understand the lights and shadows of this practice,Lesiones relacionadas con la vaina de acceso ureteral frente a infecciones postoperatorias. ?Es siempre necesaria la inserci{\'o}n de la vaina de acceso? Estudio prospectivo aleatorizado para comprender las luces y sombras de esta pr{\'a}ctica

Objective: To compare intraoperative ureteral injuries in RIRS with UAS insertion with the rate of postoperative infections after RIRS without UAS insertion. Patients and methods: In this randomized trial, patients who received an indication for RIRS between January 2017 and December 2017 were divided into two groups. Group A had no UAS insertion and Group B had UAS insertion. Post-Ureteroscopic Lesion Scale (PULS) grading was performed after UAS or flexible ureteroscope removal. Proximal, middle and distal ureteral lesions were evaluated and compared according to the PULS scale. Additionally, patients in both groups were followed postoperatively to assess any infective complication. Results: The evaluation comprised 181 patients, 89 for group A and 92 for group B. Overall stone-free rate, clinically insignificant residual fragments, and final stone-free rate were 41.4%, 53.5%, and 95%, respectively. There were 33 (37.1%) patients with ureteral lesions in group A while 42 (45.6%) patients had ureteral lesions in group B, with no significant difference. On the other hand, the overall presence of postoperative infection rate was much higher for Group A (37.1% vs 16.3% P = 0.03). Conclusions: UAS insertion does not result in a higher number of ureteral injuries. UAS insertion during RIRS allows a lower rate of postoperative infections.