Evaluation of Different Methods for Preoxygenation

The goal of this randomised cross-over study is to compare pre-oxygenation using a standard nasal cannula to pre-oxygenation using humidified high-flow nasal oxygen and a tight-fitting facemask in adult volunteers with a BMI below 30 not suffering from pulmonary or cardiac comorbidity. The main question it aims to answer is: \- Are there any differences in the effectiveness of pre-oxygenation using a standard nasal cannula compared to using a traditional facemask and pre-oxygenation using humidified high-flow nasal oxygen? Participants will be pre-oxygenated with 100% oxygen during four minutes intervals. All participants will be pre-oxygenated with various flow rates using a standard nasal cannula, a facemask and humidified high-flow nasal oxygen. End-tidal oxygen concentrations will be measured continuously in order to evaluate the effectiveness of pre-oxygenation. Each volunteer will be pre-oxygenated repeatedly, with different flow rates, with all three methods of pre-oxygenation and act as its own control. During facemask pre-oxygenation volunteers will be pre-oxygenated using both tidal volume breathing for four minutes and with eight vital capacity breaths. During pre-oxygenation using the standard nasal cannula flow rates will vary between 15 and 50 l/min. Pre-oxygenation using humidified high-flow nasal oxygen will be performed with flow rates varying between 30 and 50 l/min. Series will be conducted with volunteers breathing with both opened and closed mouth as well as with four minutes of tidal volume breathing and eight vital capacity breaths. All volunteers will start with facemask pre-oxygenation. They will thereafter be randomised to pre-oxygenation with either a standard nasal cannula or humidified high-flow nasal oxygen. Lastly, they will be pre-oxygenated with the remaining method according to the randomisation.