Thirty patients of the American Society of Anesthesiologists ( ASA ) I and II were randomly allocated into 2 groups : G1 ( n = 15 ) patients received general anesthesia and were mechanically ventilated with 9 mL/kg during 2 lung ventilations , reduced to 5 mL/kg and 5cm H2O positive end expiratory pressure ( PEEP ) during one lung ventilation ( OLV ) or GII ) ( n = 15 ) patients received TEA and the same general anesthesia and mechanical ventilation used in G1 .