This study investigates airway effects of PEEP during maskventilation at anesthesia induction. Four patient groups will be ventilated with different PEEP and driving pressures to evaluate time to open airway after start of positive pressure maskventilation during anesthesia induction.

The use of continuous positive pressure (CPAP/PEEP) during pre-oxygenation and mask-ventilation in patients undergoing anesthesia induction is increasing. Continuous positive pressures have several respiratory benefits with well-documented data on both spontaneously breathing patients and intubated patients. However the effects of PEEP on anesthetized patients during mask-ventilation is poorly investigated. In a previous trial the that the investigators conducted, a PEEP-level of 10 cmH2O during mask ventilation after anesthesia induction surprisingly delayed time to alveolar ventilation compared to ZEEP. In order to investigate this phenomenon, four groups of patients will be compared during preoxygenation and mask ventilation after anesthesia induction.

Each group consisting of 30 patients will be pre-oxygenated and mask ventilated with different CPAP/PEEP levels and different driving pressures. Time to open airway is measured as number of respiratory cycles until detection of CO2 on the capnograph.

Inclusion Criteria:

1. ≥ 18- ≤ 65 years male or female.
2. Elective surgery under general anesthesia
3. ASA-classification 1-3
4. Signed and dated informed consent

Exclusion Criteria:

1. BMI > 30
2. Predicted difficult mask-ventilation
3. Known hiatus hernia or GERD