Immediately following birth, infant survival depends on a prompt and orderly conversion to air breathing. Fluid-filled alveoli expand with air, perfusion must be established, and oxygen and carbon dioxide exchanged.
The newborn begins to breathe and cry almost immediately after birth, indicating the establishment of active respiration. Factors that appear to influence the first breath of air include:
Physical stimulation, such as handling the neonate during delivery
Deprivation of oxygen and accumulation of carbon dioxide, which serve to increase the frequency and magnitude of breathing movements both before and after birth (Dawes, 1974)
Compression of the thorax, which during pelvic descent and vaginal birth forces an amount of fluid from the respiratory tract equivalent to about a fourth of the ultimate functional residual capacity (Saunders and Milner, 1978).
Aeration of the newborn lung does not involve the inflation of a collapsed structure, but instead, the rapid replacement of bronchial and alveolar fluid by air. After delivery, the residual alveolar fluid is cleared through the pulmonary circulation and to a lesser degree, through the pulmonary lymphatics (Chernick, 1978). Delay in removal of fluid from the alveoli probably contributes to the syndrome of transient tachypnea of the newborn (TTN) (Guglani and co-workers, 2008). As fluid is replaced by air, the compression of the pulmonary vasculature is reduced considerably and in turn, resistance to blood flow is lowered. With the fall in pulmonary arterial blood pressure, the ductus arteriosus normally closes (see Fig. 4-12).
High negative intrathoracic pressures are required to bring about the initial entry of air into the fluid-filled alveoli. Normally, from the first breath after birth, progressively more residual air accumulates in the lung, and with each successive breath, lower pulmonary opening pressure is required. In the normal mature newborn, by approximately the fifth breath, pressure-volume changes achieved with each respiration are very similar to those of the adult. Thus, the breathing pattern shifts from the shallow episodic inspirations characteristic of the fetus to regular, deeper inhalations (see Chap. 15, Fetal Breathing). Surfactant—synthesized by type II pneumocytes and already present—lowers alveolar surface tension and thereby prevents collapse of the lung with each expiration. Lack of sufficient surfactant, common in preterm infants, leads to the prompt development of respiratory distress syndrome (see Chap. 29, Respiratory Distress Syndrome).
Before and during delivery, careful consideration must be given to several determinants of neonatal well-being including: (1) health status of the mother; (2) prenatal complications, including any suspected fetal malformations; (3) gestational age; (4) labor complications; (5) duration of labor and ruptured membranes; (6) type and duration of anesthesia; (7) difficulty with delivery; and (8) medications given during labor and their amounts, times given, and routes of administration.
The American Academy of Pediatrics and the American College of Obstetricians and Gynecologists (...