From Liquid to Air: Breathing after Birth

Abstract

The first breaths after birth are characterized by a rapid transition from liquid- to air-filled lungs. Air is drawn into the lung during inspiration, and some remains at end expiration to establish an end-expiratory gas volume or functional residual capacity (FRC). This is usually marked by a cry, often misinterpreted as a protest from the baby. Some infants, especially those born preterm, require respiratory support during this transitional phase. To do this effectively, we need to understand the normal physiological processes occurring at this time. Sometimes it can be difficult to aerate the lungs of preterm infants with intermittent positive pressure ventilation with pressures recommended in international guidelines, particularly when the infant does not breathe and aeration is completely dependent on the inflation pressures. Studies have shown that intermittent positive pressure ventilation should be performed without high tidal volumes to avoid damaging the lung while establishing the FRC. 1,2 However, since the use of antenatal steroids, more very preterm infants breathe spontaneously at birth, only requiring support from nasal continuous positive airway pressure. Understanding the normal spontaneous breathing pattern after birth is essential for developing safe, efficient ventilatory strategies when breathing is inadequate. Numerous physiological studies immediately after birth of spontaneously breathing infants were published between 1960 and 1986. 3-10 However, little new data are currently available on this topic, reflecting the difficulties of performing these studies. This review will discuss what happens during the first breaths of air with the emphasis on where the liquid goes and the current knowledge about the spontaneous breathing pattern adopted by infants immediately after birth.