Treatment of apnea of prematurity involves administration of oxygen to hypoxic infants, transfusion of anemic infants, and physical cutaneous stimulation for infants with mild apnea. Methylxanthines (caffeine or theophylline) are the mainstay of pharmacologic treatment of apnea. Xanthine therapy increases minute ventilation, improves the carbon dioxide sensitivity, decreases hypoxic depression of breathing, enhances diaphragmatic activity, and decreases periodic breathing. Treatment usually is initiated with a loading dose followed by maintenance therapy. High-flow nasal cannula therapy and nasal continuous positive airway pressure of 4 to 6 cm H2O also are effective and relatively safe methods of treating obstructive or mixed apneas; they may work by stimulating the infant and splinting the upper airway. Continuous positive airway pressure also probably increases functional residual capacity, improving oxygenation.
Embryonic hematopoiesis begins by the 20th day of gestationand is evidenced as blood islands in the yolk sac. In midgestation, erythropoiesis occurs in the liver and spleen; the bonemarrow becomes the predominant site in the last trimester.Hemoglobin concentration increases from 8 to 10 g/dL at12 weeks to 16.5 to 18 g/dL at 40 weeks. Fetal red blood cell(RBC) production is responsive to erythropoietin; the concentration of this hormone increases with fetal hypoxia and anemia.
After birth, hemoglobin levels increase transiently at 6 to 12 hours, then decline to 11 to 12 g/dL at 3 to 6 months. A premature infant (<32 weeks’ gestational age) has a lower hemoglobin concentration and a more rapid postnatal decline of hemoglobin level, which achieves a nadir 1 to 2 months after birth. Fetal and neonatal RBCs have a shorter life span (70 to 90 days) and a higher mean corpuscular volume (110 to 120 fL) than adult cells. In the fetus, hemoglobin synthesis in the last two trimesters of pregnancy produces fetal hemoglobin (hemoglobin F), composed of two alpha chains and two gamma chains. Immediately before term, the infant begins to synthesize beta-hemoglobin chains; the term infant should have some adult hemoglobin (two alpha chains and two beta chains). Fetal hemoglobin represents 60% to 90% of hemoglobin at term birth. The levels decline to adult levels of less than 5% by 4 months of age.
For a term infant, blood volume is 72 to 93 mL/kg, and for a preterm infant, blood volume is 90 to 100 mL/kg. The placenta and umbilical vessels contain approximately 20 to 30 mL/kg of additional blood that can increase neonatal blood volume and hemoglobin levels transiently for the first 3 days of life if clamping or milking (stripping) of the umbilical cord is delayed at birth. Delayed clamping may increase the risk of polycythemia and jaundice, but it improves glomerular filtration. Early clamping may lead to anemia, a cardiac murmur, poor peripheral perfusion, and less tachypnea. Hydrostatic pressure affects blood transfer between the placenta and the infant at birth. An undesired fetal-to-placental transfusion occurs if the infant is situated above the level of the placenta.
The physiologic anemia noted at 2 to 3 months of age in term infants and at 1 to 2 months of age in preterm infants is a normal process that does not result in signs of illness and does not require any treatment. It is a physiologic condition believed to be related to several factors, including increased tissue oxygenation experienced at birth, shortened RBC life span, and low erythropoietin levels.
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