Disorders of transition

1.5. Disorders of transition

Why do some newborns fail to undergo a successful transition to extra-uterine life?

Failure of the newborn to establish effective breathing at birth and undergo successful transition may be the result of fetal compromise before labour, during labour or after birth. Prior to birth and during labour, any event that compromises placental function or blood flow through the umbilical cord can lead to fetal hypoxia. Problems that occur after birth are more likely to involve the newborn’s airway and/or lungs (Kattwinkel, 2006).

Before or during labour

Events that compromise uterine, placental or cord blood flow:

• Antepartum haemorrhage
• Placental abruption
• Cord prolapse
• Cord compression
• Cord tightly around the neck
• Maternal pre-eclampsia

At the time of birth

Lung aeration is central to the transition to extra-uterine life. If breathing is not initiated following birth, pulmonary vascular resistance will not decrease and oxygen cannot reach the blood circulating through the lungs. As a result, the newborn will become hypoxaemic. There are various reasons why a newborn infant may fail to establish effective breathing at the time of birth:

• If the newly born infant does not breathe sufficiently to force liquid from the alveoli into the tissue, air cannot enter the alveoli and hypoxaemia results
• Extremely pre-term infants may not be able to generate sufficient hydrostatic pressure gradients during inspiration to clear the airways of liquid and allow air to enter the very distal gas exchange regions (Siew, et al., 2009)
• If material such as meconium or blood is blocking the airway, air cannot enter the alveoli and hypoxemia results
• If there is an underlying structural malformation of the airway, the newborn may not be able to breathe effectively despite efforts to do so. Structural problems include (but are not limited to):
  • A blockage of the airway by bony cartilage (choanal atresia)
  • A blockage of the airway by a laryngeal web
  • A pharyngeal airway malformation (e.g. Pierre Robin Syndrome/Sequence)
  • Lungs that have failed to form properly (hypoplastic lungs)
• If the newly born infant develops a significant air leak (e.g. pneumothorax) either spontaneously or as a result of being over-ventilated (i.e. an excessive volume of gas delivered by a manual ventilation device)
• Other reasons for failure to breathe after birth include:
  • Effects of maternal medications
  • Magnesium sulphate
  • Narcotics
  • Birth by caesarean section under general anaesthetic
  • Birth injury (e.g. cervical spine fracture)
  • Intra-uterine infection
  • Neuromuscular disorders

If effective ventilation is not established the following will occur:

• Bradycardia
  • As a result of lack of oxygen to the myocardium
• Respiratory drive will be further depressed
  • As a result of lack of oxygen to the brain stem
• Blood pressure will continue to fall
  • As a result of hypoxia, bradycardia and poor cardiac contractility
• Cyanosis (beyond 10 minutes of birth)
  • As a result of hypoxaemia (insufficient oxygen in the blood)
• Poor muscle tone
  • As a result of insufficient oxygen delivery to the brain, muscles and other organs