Preoxygenation in adult anaesthesia is usually achieved using Face mask oxygenation and bag-mask ventilation with risk of gastric insufflation, leading to increased intragastric pressure and raised risk of pulmonary aspiration of stomach contents. High flow nasal cannula (HFNC) oxygenation is gaining popularity in modern anaesthesia with an increase of apneic oxygenation time, causing continuous positive airway pressure and carbon dioxide clearance. However, data on gastric insufflation during HFNC oxygenation is sparse. Hence we aim to compare gastric insufflation during HFNC oxygenation and conventional face mask ventilation in adult anaesthesia using objective measurement of ultrasonographic gastric antral area.

After obtaining institutional ethical committee approval, 50 patients requiring general anaesthesia with elective intubation of age group 18 to 60 years belonging to ASA class I to III will be enrolled in this study after obtaining informed consent. Computer generated randomisation will be used to allocate 25 patients in each of the two groups. Study group patients will be receiving HFNC oxygenation using humidified 100% oxygen with initial flows of 40 litres/minute, gradually increasing flows to 70 litres/minute over one minute and continued during induction till completion of intubation along with jaw thrust after induction. The control group patients will be receiving conventional face mask preoxygenation using fresh gas flows of 10 litres/minute 100% oxygen with snuggly held face mask via a breathing system of anaesthesia workstation until induction followed by volume controlled ventilation using a tidal volume of 8ml/kg with a frequency of 12 breaths/minute along with oral airway and jaw thrust until intubation.

For all patients to assess gastric insufflation during preoxygenation, gastric antral area will be measured using low frequency curvilinear probe of ultrasound prior to start of preoxygenation as baseline values and just prior to intubation. The appearance of comet tail sign in gastric antrum during preoxygenation using continuous ultrasonographic assessment will be recorded as a subjective finding of gastric insufflation. Arterial line will be secured to all patients for collecting ABG samples prior to preoxygenation, prior to induction and prior to intubation in assessing the rise in PaCO2 values.

Data recorded in case report forms will be entered in an excel sheet for statistical calculation and analysis using statistical methods student t test and chi-square test. P value <0.05 will be considered as significant.