Anesthesia was induced with fentanyl (2 μg/kg) and propofol (2mg/kg). When patients were unconscious, original or generic sevoflurane was administered. Tracheal intubation was facilitated by administering rocuronium 0.6 mg/kg. The lungs of the patients were then ventilated with oxygen in air (1:2), and the ventilation rate was adjusted to maintain the end-tidal carbon dioxide partial pressure between 35 and 45 mmHg. The concentrations of carbon dioxide, sevoflurane, and oxygen were measured continuously using an infrared anesthetic gas analyzer (Datex-Ohmeda S/5, Planar Systems, Inc., Beaverton, OR, USA), which was calibrated before anesthesia for each patient using a standard gas mixture.