Concretely, the observer will pre-operatively collect an informed consent form of the patient and, at the same time, asses the patient's state via QoR-40. Both groups will have a remifentanil infusion upon arrival in the PACU. A nurse, independent to the study, will prepare the adequate post-operative syringe (remifentanil diluted at 20 µg/ml or NaCl 0.9%) and will change the syringe according to pre-operative randomization.