HFNC has been shown beneficial in pre-oxygenation, oxygenation after extubation, and in the treatment of respiratory failure and heart failure. New uses in difficult airway management are now emerging. However, the main case series of HFNC use in difficult airways did not measure intra-operative airway pressures end tidal oxygen and carbon dioxide; these gases were only measured at the end of surgery and when a definitive airway was inserted. As far as the investigators are aware, there are no data on intra-operative, intra-tracheal airway pressures or oxygen or carbon dioxide during HFNC oxygenation. Our study aim is to fill this knowledge gap.