Apnoeic oxygenation in pregnancy: a modelling investigation.

Recent studies have shown that nasal oxygen delivery can prolong the time to desaturation during apnoea in the non-pregnant population. We investigated the benefits of apnoeic oxygenation during rapid sequence induction in the obstetric population using computational modelling. We used the Nottingham Physiology Simulator, and pre-oxygenated seven models of pregnancy for 3 min using Fi O2 1.0, before inducing apnoea. We found that increasing Fi O2 at the open glottis increased the time to desaturation, extending the time taken for Sa O2 to reach 40% from 4.5 min to 58 min in the average parturient model (not in labour). Our study suggests that a small increase in time to desaturation could be achieved at Fi O2 0.4-0.6, which could be delivered by standard nasal cannulae. The greatest increases in time to desaturation were seen at Fi O2 1.0, which could be delivered by high-flow nasal cannulae under ideal conditions.