The aim of the investigators is to evaluate sedation efficacy and recovery between two groups of ambulatory patients having a colonoscopy: one group will receive a manual titration of propofol, the other group a target controlled infusion (TCI) of propofol. The investigators will evaluate both groups before, during and after colonoscopy for adverse events, quality of sedation and recovery. When patients are estimated to be ready for discharge, they will also be subjected to a cognitive and a psychomotoricity test.