Preoperative data recorded : age, height, weight, ASA physical status, and history of asthma, current smoking (ex-smokers were considered after a 3 month period without smoking), number of pack-years, sign inform consent The day of surgery, randomly allocation (random number table, block sizes of 15) to one of the 3 preoxygenation methods: spontaneous breathing, noninvasive positive inspiratory pressure ventilation (PPV) at 12 centimeters of water (cmH2O) without PEEP or with PEEP at 6 cmH2O (PEEP).