Adaptation To Extrauterine Life - Breathing and Circulation

Breathing and Circulation

Perfusing its body by breathing independently instead of utilizing placental oxygen is the first challenge of a newborn. At birth, the baby's lungs are filled with fetal lung fluid (which is not amniotic fluid) and are not inflated. The newborn is expelled from the birth canal, its central nervous system reacts to the sudden change in temperature and environment. This triggers it to take the first breath, within about 10 seconds after delivery. With the first breaths, there is a fall in pulmonary vascular resistance, and an increase in the surface area available for gas exchange. Over the next 30 seconds the pulmonary blood flow increases and is oxygenated as it flows through the alveoli of the lungs. Oxygenated blood now reaches the left atrium and ventricle, and through the descending aorta reaches the umbilical arteries. Oxygenated blood now stimulates constriction of the umbilical arteries resulting in a reduction in placental blood flow. As the pulmonary circulation increases there is an equivalent reduction in the placental blood flow which normally ceases completely after about three minutes. These two changes result in a rapid redirection of blood flow into the pulmonary vascular bed, from approximately 4% to 100% of cardiac output. The increase in pulmonary venous return results in left atrial pressure being slightly higher than right atrial pressure, which closes the foramen ovale. The flow pattern changes results in a drop in blood flow across the ductus arteriosus and the higher blood oxygen content of blood within the aorta stimulates the constriction and ultimately the closure of this fetal circulatory shunt.

All of these cardiovascular system changes result in the adaptation from fetal circulation patterns to an adult circulation pattern. During this transition, some types of congenital heart disease that were not symptomatic in utero during fetal circulation will present with cyanosis or respiratory signs.

It is common obstetric practice to intervene in these changes by applying a clamp to the umbilical cord, often within 20 seconds of birth, before transition has taken place. However delayed clamping(>1min) may have benefits in terms of iron status.

Following birth, the expression and re-uptake of surfactant, which begins to be produced by the fetus at 20 weeks gestation, is accelerated. Expression of surfactant into the alveoli is necessary to prevent alveolar closure (atelectasis). At this point, rhythmic breathing movements also commence. If there are any problems with breathing, management can include stimulation, bag and mask ventilation, intubation and ventilation. Cardiorespiratory monitoring is essential to keeping track of potential problems. Pharmacological therapy such as caffeine can also be given to treat apnea in premature newborns. A positive airway pressure should be maintained, and neonatal sepsis must be ruled out.

Potential neonatal respiratory problems include apnea, transient tachypnea of the newborn (TTNB), respiratory distress syndrome (RDS), meconium aspiration syndrome (MAS), airway obstruction, and pneumonia.