The used of KALINOX® (50% nitrous oxide and oxygen) inhalation has demonstrated analgesic efficacy in various procedures (obstetric, liver biopsy, transrectal ultrasound guided prostate biopsy, emergency) The aim of this study is to investigate the safety and efficacy of analgesia with N2O/O2 inhalation for detrusor BTX-A injections using a rigid cystoscope.