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. Will be included patient with severe neurogenic detrusor overactivity but with preserved bladder sensibility treated with botulinum-A toxin injections into the detrusor muscle Patients will be randomized into a group that will receive KALINOX® via a breath activated device and a control group that receive oxygen through a similar breathing device. The investigator will be involved in the randomization process since the gas cylinders will be covered and they will be blind to the gas used. All patients involved will be blinded to the gas that they will inhale. The patients will score the injection pain and the anxiety on a 10-point rating scale. Furthermore the duration of the practice will be measured.