Physiological Principles of Newborn Resuscitation

Physiological Principles of Newborn Resuscitation

It is normal for the fetus to experience transient hypoxia as placental blood flow is compromised during contractions in the second stage of labour, and this is usually well tolerated. The fetus that suffers prolonged hypoxia in utero, however, will require active resuscitation at birth.

Transition from the fetal to the normal newborn state requires a range of physiological changes, including aeration of the fluid filled lungs so that gas exchange is transferred from the placental circulation to the lungs of the newborn baby. The normal response to hypoxia of the newborn infant who does not breathe effectively after birth is to become apnoeic ('primary apnoe'’); the heart rate is initially normal, but the bay will then become bradycardic as the myocardium becomes hypoxic. The circulation tot the kidneys is reduced.

If the baby remains hypoxic, gasping respirations will develop. If these efforts fail to aerate the lungs, breathing attempts will fade and the baby will become apnoeic again ('secondary' or 'terminal' apnoea). The baby will then become increasingly hypoxic and acidotic, the heart will fail and the baby will die. This process may take up to 20 minutes in the term newborn. The priority during resuscitation of the newborn is therefore to establish effective aeration of the lungs, so that oxygenated blood is delivered to the heart, cardiac function is restored, and oxygenated blood is delivered to the neural centres in the brain so that respiration is maintained.

Simple ventilation of the lungs is sufficient in the vast majority of cases, if there has been a prolonged hypoxic insult, either in utero or after birth, the baby may also require cardiac compression to deliver oxygenated blood from the lungs to the heart, some babies who have been severely hypoxic may also require drugs to restore the circulation - the outlook for these babies is poor.

Formal assessment of the newborn is traditionally described using the Apgar score shown in Table 6.1. The score is used to describe the status of the baby at one minute and the response to resuscitation when reassessed at 5 minutes.

Resuscitation of the baby should start immediately if required after delivery, and should not be delayed until the 1-minute score is assessed. A score of 3 critically low and a score of 7-10 at 5 minutes is normal. A baby who scores less than 7 at 5 minutes should be reassessed every 5 minutes up to 20 minutes. A score of less than 3 at 10, 15 and 20 minutes predicts poor outcome.