The new MIRUS system as well as the established AnaConDa system uses a reflector to conserve volatile anaesthetics (VA). Both systems act with commercially available ICU ventilators. In contrast to AnaConDa the MIRUS includes an automated control of end-tidal VA concentrations. In this study the investigators compared feasibility, costs and recovery times after anaesthesia with isoflurane (ISO), sevoflurane (SEVO) or desflurane (DES) in ventilated and spontaneously breathing patients.