Ventilation and Gastric Insufflation During Three Levels of Inspiratory Pressure During Mask Ventilation

Upon arrival to the operating room, routine monitors (ECG, pulse oximetry, and non-invasive blood pressure monitor) will be applied, intravenous line will be secured, and routine pre-medications (ranitidine 50 mg and midazolam 3-5 mg) will be administrated. End-tidal CO2 monitoring will be initiated after induction of general anesthesia and starting face-mask ventilation. Induction of anesthesia will be achieved using fentanyl (2 mcg/Kg), propofol (2 mg/Kg), and rocuronium (0.6 mg/Kg). After loss of verbal response, mask ventilation will be achieved by appropriate size face mask and oropharyngeal airway with 100% oxygen and double hand jaw thrust head tilt maneuver. The included patients will be randomly allocated to receive the assigned pressure-controlled mask ventilation. The 3 study groups will receive the planned inspiratory pressure, without positive end-expiratory pressure, with a respiratory rate of 15, and inspiratory to expiratory ratio of 1:2 for 180 seconds.

Assessment gastric insufflation during mask ventilation will be achieved by ultrasound assessment of gastric antrum (in the sagittal plane between left lobe of the liver and pancreas at level of the aorta) and auscultation by two blinded investigators to the assigned pressure. The ultrasound screen will be positioned to be not visible to the investigator responsible for auscultation. Gastric insufflation will be identified by comet-tail sign by gastric ultrasound and gurgling sound by auscultation.

Gastric antrum cross sectional area [ D1(longitudinal diameter) X D2 (anteroposterior diameter) X π /4] in between contractions in supine position before face mask ventilation and after insertion of endotracheal tube will be recorded. gastric insufflation will be identified if gastric antrum cross sectional area increased by > 30% after endotracheal intubation in relation to the baseline.

During mask ventilation, the following parameter will be recorded at 30, 60, 90,120, 150 and 180 seconds; peripheral oxygen saturation, the end-tidal carbon dioxide concentration , peak airway measured pressure, and tidal volume Demographic data (age, sex, weight, height, BMI, comorbidities) will be recorded.