Physiological Processes

During fetal life, gas exchange is undertaken at the placenta as the lungs are liquid-filled. During normal labour uterine contractions interfere with placental gas exchange. Maternal and fetal hormonal influences during labour encourage absorption of the fetal lung fluid from the alveolar spaces to prepare for air breathing.

In some cases, intrauterine hypoxia can occur which may also lead to hypercarbia, and the stimulation from respiratory centres become more frequent causing ‘breathing’ to become deeper and rapid. PaO2 reduces and PaCO2 increases leading to the development of acidaemia due to the production of lactic acid as a by-product of anaerobic metrabolism.

The fetus will lose consciousness and breathing movements cease as the fetus enters a period known as ‘Primary Apnoea’. At this point the heart rate will begin to reduce to about 1/2 its normal rate, and the cardiac cells will switch to anaerobic metabolism.

If this insult continues, primitive spinal centres produce stimuli and result in deep gasping and further allowing the function of some cardio-pulmonary circulation – if these gasps fail to aerate the lungs then this process declines as increasing acidosis and hypoxia impact synaptic communication.

The fetus then enters a stage known as ‘Terminal Apnoea’ and without further intervention the fetus will die.

A baby born, who is not breathing within a minute or two of birth may be in any of the stages of apnoea mentioned previously and therefore a systematic approach utilising the Newborn Life Support Algorithm is required to enable transition to extrauterine life and provide support where required.