The investigators and other groups have demonstrated that high-flow nasal oxygen used during preoxygenation for emergency surgery is at least equally effective as preoxygenation compared to standard tight fitting mask. The investigators also have data from a recent study that indicates that high-flow nasal oxygen might decrease the risk of clinically relevant desaturation below 93% of arterial oxygen saturation.

The studies investigating the concept of high-flow nasal oxygen has up to this date excluded pregnant women. Pregnant woman is a patient group with known difficulties to maintain adequate saturation levels during apnoea. Due to smaller functional residual capacity their oxygen stores after preoxygenation are smaller compared to patients with a normal body mass index. The pregnant woman also have a higher oxygen demand and metabolism due to the growing placenta and the fetus. Pregnant women are therefore a patient group where a method that could prolong time until desaturation would be even more valuable and potentially could save lives.

Based on the above, the investigators now aim to conduct a clinical pilot study, where pregnant women undergoing caesarian section under general anesthesia are pre and perioxygenated with high-flow nasal oxygen. Data from that group will be compared with patients preoxygenated in a traditional manner with tight facemask. This study is done to evaluate an established technique on a patient category that in theory could gain a lot from it.

Inclusion Criteria:

1. Adult, >18 years old
2. Caesarian section under general anesthesia.
3. Pregnant in week 30 or later
4. Capable of understanding the study information and signing the written consent.

Exclusion Criteria:

1. BMI >45
2. Dependency on non-invasive ventilation to maintain oxygen saturation