All patients will be mechanically ventilated with a tidal volume of 6-8 mL/kg and a respiratory rate of 12 - 14 to achieve end-tidal CO2 30 - 35 mmHg . A PEEP of 5 cm H2O is also added. FiO2 will be adjusted to achieve a PaO2 between 200 and 300 mmHg. Isoflurane will be adjusted to 1 - 1.5 expired MAC , as well as fentanyl increments of 2 μg/Kg will be used to control adequate level of anesthesia and to maintain hemodynamic stability. Incremental doses of pancuronium will be administered as needed.