General anesthesia will be induced by bolus administration of propofol (2-3 mg/kg) and fentanyl (1-2 mcg/kg), and maintained with an inhalational agent. Rocuronium (0.6 mg/kg) will be administered, after face mask ventilabilty being checked, to provide muscle relaxation and a mixture of sevoflurane or isoflurane and nitrous oxide (per anesthesiologist choice) will be utilized for maintenance of anesthesia once the ability to mask ventilate is confirmed. The lungs will be mechanically ventilated with a semi-closed circle system to maintain an end-tidal CO2 near 35 mmHg. Patients' lungs will be ventilated via an anesthesia mask for five minutes with 100% oxygen until the patient is completely relaxed.