Maternal hypoxaemia during labor.

A review is given covering four different series of studies revealing maternal hypoxaemia during labour, in spite of normal maternal heart and lung function. The previous Swedish use of 100% nitrous oxide inhalation during contractions lead to serious maternal hypoxaemia. The use of pethidine in combination with hyperventilation during the contractions leads to long respiratory pauses and maternal hypoxaemia in between the contractions. Excessive hyperventilation during the contractions may in itself lead to a so called hyperventilation-hypoventilation syndrome with maternal hypoxaemia. Finally excessive sustained pushing with maximal effort and no ventilation also leads to maternal hypoxaemia. Thus maternal hypoxaemia, although largely unknown is not too infrequent and is mainly of iatrogenic origin. Proper knowledge should suffice for prevention.