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Ebook Manual of neonatal care (7/E): Part 2

(BQ) Part 2 book "Manual of neonatal care" has contents: Common neonatal procedures, skin care, disorders of sex development, inborn errors of metabolism, orthopaedic problems, neural tube defects, neonatal seizures, intracranial hemorrhage, lyme disease, congenital toxoplasmosis,. and other contents. | 45 Anemia Helen A. Christou I. HEMATOLOGIC PHYSIOLOGY OF THE NEWBORN (1–5). Significant changes occur in the red blood cell (RBC) mass of an infant during the neonatal period and ensuing months. The evaluation of anemia must take into account this developmental process, as well as the infant’s physiologic needs. A. Normal development: The physiologic anemia of infancy (1) 1. In utero, the fetal aortic oxygen saturation is 45%, the erythropoietin levels are high, and the RBC production is rapid. The fetal liver is the major site of erythropoietin production. 2. After birth, the oxygen saturation is 95%, and the erythropoietin is undetectable. RBC production by day 7 is 1/10th the level in utero. Reticulocyte counts are low, and the hemoglobin level falls (see Table 45.1). 3. Despite dropping hemoglobin levels, the ratio of hemoglobin A to hemoglobin F increases and the levels of 2,3-diphosphoglycerate (2,3-DPG) (which interacts with hemoglobin A to decrease its affinity for oxygen, thereby enhancing oxygen release to the tissues) are high. As a result, oxygen delivery to the tissues actually increases. This physiologic “anemia” is not a functional anemia in that oxygen delivery to the tissues is adequate. Iron from degraded RBCs is stored. 4. At 8 to 12 weeks, hemoglobin levels reach their nadir (see Table 45.2), oxygen delivery to the tissues is impaired, renal erythropoietin production is stimulated, and RBC production increases. 5. Infants who have received transfusions in the neonatal period have lower nadirs than normal because of their higher percentage of hemoglobin A (1). 6. During this period of active erythropoiesis, iron stores are rapidly utilized. The reticuloendothelial system has adequate iron for 15 to 20 weeks in term infants. After this time, the hemoglobin level decreases if iron is not supplied. B. Anemia of prematurity is an exaggeration of the normal physiologic anemia (Tables 45.1 and 45.2). 1. RBC mass and iron stores are decreased because