Health Problems of the Newborn

The most profound physiologic change required of the newborn is the transition from intrauterine to extrauterine existence. Onset of respiration must begin at birth for sur­vival. The first breath expands the alveoli and initiates gas exchange. The infant's respiratory rate initially is rapid and primarily abdominal, but with maturation, the respiratory rate gradually slows. Birth also initiates major changes in the cardiovascular system. The fetal shunts, the foramen ovale and ductus arteriosus, begin to close, and the circu­lation of blood changes from a serial to a parallel circuit. (See Chapter 26 for further discussion.)

In addition to establishing respiration, heat regulation is another response critical to the infant's survival. At birth, the newborn's temperature is about 0.5°C higher than the mother's temperature. The temperature gradient causes vasodilation; thus, heat is lost rapidly, especially in a cold delivery room. The newborn's large surface area and lack of subcutaneous fat predisposes to excessive heat loss. Marked heat loss and the consequent lowering of body temperature can cause an otherwise healthy newborn to develop respi­ratory distress.