Measurements
Before the entry into the operating room, we collected the following preoperative data: age, sex, height, weight, neck, hip and waist circumference, Mallampati and ASA score, FEVFrom the moment the ventilator circuit was connected to the mouthpiece, inspiratory and expiratory fractions of oxygen, carbon dioxide and minute ventilation were continuously monitored and displayed on the anesthesia machine (Dräger Primus, Lübeck, Germany). The time required to obtain a FetO