Study design
Patients fasted for 8 h and received oral ranitidine 150 mg the evening before and the morning of their bariatric surgery. After the intravenous placement and application of standard American Society of Anesthesiologist (ASA) physiological monitors, the attending anesthesiologist evaluated the airway to decide if the patient could participate in the study. The patient was randomized if the anesthesiologist judged the patient’s airway not at risk of difficult mask ventilation or intubation. Sequentially numbered opaque envelopes prepared by an independent research assistant, in clusters of ten in a 1:1 ratio, were used for randomization between the two groups (RP/ZEEP versus RT/PPV).Before the start of the preoxygenation, for patients in group 1 (RP/ZEEP), the operating table (Universal operating table, Alphamaxx, Maquet, Rastatt, Germany) was set in a 25º beach-chair position (upper body portion was tilted upward at a 25º angle). The anesthesia ventilator (Dräger Primus, Lübeck, Germany) was set in spontaneous ventilation without any positive pressure ventilation with the adjustable pressure-limiting valve sets in the open position. The beach chair position used in our study is similar to the ramp position [Design of the intervention. Both groups had a 3-min preoxygenation with an inspiratory fraction of oxygen (FiOIn both groups, the inspiratory fraction of oxygen was set to 1.0, and the fresh gas flow was set to 18 L/min. The ventilatory interface used during preoxygenation was a soft mouthpiece (Airlife adult flexible mouthpiece, CareFusion, San Diego, CA, USA) with a nose clip instead of a facemask to prevent air leaks, given the high tolerability previously observed with this device in a similar study population [