Pre-oxygenation and apnoea in pregnancy: changes during labour and with obstetric morbidity in a computational simulation.

Using the Nottingham Physiology Simulator, we investigated the effects on pre-oxygenation and apnoea during rapid sequence induction of labour, obesity, sepsis, pre-eclampsia, maternal haemorrhage and multiple pregnancy in term pregnancy. Pre-oxygenation with 100% oxygen was followed by simulated rapid sequence induction when end-tidal nitrogen tension was less than 1 kPa, and apnoea. Labour, morbid obesity and sepsis accelerated pre-oxygenation and de-oxygenation during apnoea. Fastest pre-oxygenation was in labour, with 95% of the maximum change in expired oxygen tension occurring in 47 s, compared to 97 s in a standard pregnant subject. The labouring subject with a body mass index of 50 kg x m(-2) demonstrated the fastest desaturation, the time taken to fall to an arterial saturation < 90% being 98 s, compared to 292 s in a standard pregnant subject. Pre-eclampsia prolonged pre-oxygenation and tolerance to apnoea. Maternal haemorrhage and multiple pregnancy had minor effects. Our results inform the risk-benefit comparison of the anaesthetic options for Caesarean section.