Pre-oxygenation before anaesthesia induction is mostly performed using a tight-fitting facemask. Recently, studies have shown that pre-oxygenation using humidified high-flow nasal oxygen is equally effective as pre-oxygenation using a standard tight-fitting facemask. Pre-oxygenation using humidified high-flow nasal oxygen has several potential advantages including improved patient comfort and the possibility of a seamless transition from pre-oxygenation to apnoeic oxygenation. Unfortunately, this technique requires an additional machine which can be expensive and also difficult to use in settings outside a hospital.~In this study, pre-oxygenation using a standard nasal cannula delivering a high flow of oxygen will be compared with standard facemask pre-oxygenation and pre-oxygenation using humidified high-flow nasal oxygen 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.
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.